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Android Getting Started

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Welcome to Android!

The Android platform is a software stack for mobile devices including an operating system, middleware and key applications. Developers can create applications for the platform using the Android SDK. Applications are written using the Java programming language and run on Dalvik, a custom virtual machine designed for embedded use which runs on top of a Linux kernel.

If you want to know how to develop applications for Android, you're in the right place. This site provides a variety of documentation that will help you learn about Android and develop mobile applications for the platform.

An early look at the the Android SDK is also available. It includes sample projects with source code, development tools, an emulator, and of course all the libraries you'll need to build an Android application.

Download the SDK

To start learning about the Android platform, please read the documentation in the following order:

What is Android?
An overview of the Android platform
Getting Started
All the basics, including Hello World
Developing Applications
The nuts and bolts of Android applications
Developer Toolbox
In-depth information on specific topics
Reference Information
A myriad of reference material
Sample Code
Several sample Android applications for your viewing pleasure
Frequently Asked Questions
Common issues and questions

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What is Android?

Android is a software stack for mobile devices that includes an operating system, middleware and key applications. This early look at the Android SDK provides the tools and APIs necessary to begin developing applications on the Android platform using the Java programming language.

Features

  • Application framework enabling reuse and replacement of components
  • Dalvik virtual machine optimized for mobile devices
  • Integrated browser based on the open source WebKit engine
  • Optimized graphics powered by a custom 2D graphics library; 3D graphics based on the OpenGL ES 1.0 specification (hardware acceleration optional)
  • SQLite for structured data storage
  • Media support for common audio, video, and still image formats (MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)
  • GSM Telephony (hardware dependent)
  • Bluetooth, EDGE, 3G, and WiFi (hardware dependent)
  • Camera, GPS, compass, and accelerometer (hardware dependent)
  • Rich development environment including a device emulator, tools for debugging, memory and performance profiling, and a plugin for the Eclipse IDE

Android Architecture

The following diagram shows the major components of the Android operating system. Each section is described in more detail below.

Android System Architecture

Applications

Android will ship with a set of core applications including an email client, SMS program, calendar, maps, browser, contacts, and others. All applications are written using the Java programming language.

Application Framework

Developers have full access to the same framework APIs used by the core applications. The application architecture is designed to simplify the reuse of components; any application can publish its capabilities and any other application may then make use of those capabilities (subject to security constraints enforced by the framework). This same mechanism allows components to be replaced by the user.

Underlying all applications is a set of services and systems, including:

  • A rich and extensible set of Views that can be used to build an application, including lists, grids, text boxes, buttons, and even an embeddable web browser
  • Content Providers that enable applications to access data from other applications (such as Contacts), or to share their own data
  • A Resource Manager, providing access to non-code resources such as localized strings, graphics, and layout files
  • A Notification Manager that enables all applications to display custom alerts in the status bar
  • An Activity Manager that manages the life cycle of applications and provides a common navigation backstack

For more details and a walkthrough of an application, see Writing an Android Application.

Libraries

Android includes a set of C/C++ libraries used by various components of the Android system. These capabilities are exposed to developers through the Android application framework. Some of the core libraries are listed below:

  • System C library - a BSD-derived implementation of the standard C system library (libc), tuned for embedded Linux-based devices
  • Media Libraries - based on PacketVideo's OpenCORE; the libraries support playback and recording of many popular audio and video formats, as well as static image files, including MPEG4, H.264, MP3, AAC, AMR, JPG, and PNG
  • Surface Manager - manages access to the display subsystem and seamlessly composites 2D and 3D graphic layers from multiple applications
  • LibWebCore - a modern web browser engine which powers both the Android browser and an embeddable web view
  • SGL - the underlying 2D graphics engine
  • 3D libraries - an implementation based on OpenGL ES 1.0 APIs; the libraries use either hardware 3D acceleration (where available) or the included, highly optimized 3D software rasterizer
  • FreeType - bitmap and vector font rendering
  • SQLite - a powerful and lightweight relational database engine available to all applications

Android Runtime

Android includes a set of core libraries that provides most of the functionality available in the core libraries of the Java programming language.

Every Android application runs in its own process, with its own instance of the Dalvik virtual machine. Dalvik has been written so that a device can run multiple VMs efficiently. The Dalvik VM executes files in the Dalvik Executable (.dex) format which is optimized for minimal memory footprint. The VM is register-based, and runs classes compiled by a Java language compiler that have been transformed into the .dex format by the included "dx" tool.

The Dalvik VM relies on the Linux kernel for underlying functionality such as threading and low-level memory management.

Linux Kernel

Android relies on Linux version 2.6 for core system services such as security, memory management, process management, network stack, and driver model. The kernel also acts as an abstraction layer between the hardware and the rest of the software stack.

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Getting Started with Android

To get started with Android, please read the following sections first:

Installing the SDK and Plugin
How to install the SDK and Eclipse plugin, or how to use other tools to build Android applications. Also a guide to running the sample applications.
Hello Android!
Writing your first Android Application, the ever popular Hello World, Android style.
Anatomy of an Android Application
A guide to the structure and architecture of an Android Application. This guide will help you understand the pieces that make up an Android app.
Tutorial: Building a Full Android Application
This tutorial document will lead you through constructing a real Android Application: A notepad which can create, edit and delete notes, and covers many of the basic concepts with practical examples.
Development Tools
The command line tools included with the SDK, what they do, and how to use them.
Life Cycle of an Android Application
The important life-cycle details for Applications and Activities running inside of them.

Other Introductory Material

After reading the sections above, the following Getting Started information is also very useful:

Core Packages

These are the basic packages that make up the Android SDK for writing applications. The packages are organized as layers, listed here from lowest-level to highest.

android.util
contains various low-level utility classes, such as specialized container classes, XML utilities, etc.
android.os
provides basic operating system services, message passing, and inter-process communication.
android.graphics
is the core rendering package.
android.text, android.text.method, android.text.style, and android.text.util
supply a rich set of text processing tools, supporting rich text, input methods, etc.
android.database
contains low-level APIs for working with databases.
android.content
provides various services for accessing data on the device: applications installed on the device and their associated resources, and content providers for persistent dynamic data.
android.view
is the core user-interface framework.
android.widget
supplies standard user interface elements (lists, buttons, layout managers, etc) built from the view package.
android.app
provides the high-level application model, implemented using Activities.

Other Notable Packages

These packages provide additional domain-specific features of the Android platform. They are not necessary for basic application development.

android.provider
contains definitions for various standard content providers included with the platform.
android.telephony
provides APIs for interacting with the device's phone stack.
android.webkit
includes various APIs for working with web-based content.

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Installing the SDK

This page describes how to install the Android SDK and set up your development environment. If you haven't downloaded the SDK yet, you can use the link below to get started. Then read the rest of this document to learn how to install, configure, and use the SDK to create Android applications.

Download the SDK

Upgrading?

If you have already downloaded an earlier version of the SDK and developed applications on it, please read the Upgrading the SDK document instead. The Upgrading document explains how to migrate your existing development environment and applications to the new SDK release. The document also provides information that you will find useful during the upgrade, such as lists of framework and API changes.

Contents

System and Software Requirements
Installing the SDK
Installing the Eclipse Plugin (ADT)
Developing Android Applications on Eclipse
Developing Android Applications with Other IDEs and Tools
Debugging
Debug and Test Settings on the Device
Top Debugging Tips
Building and Installing an Android Application
Removing an Android Application
Eclipse Tips

System and Software Requirements

To develop Android applications using the code and tools in the Android SDK, you need a suitable development computer and development environment, as described below.

Supported Operating Systems

  • Windows XP or Vista
  • Mac OS X 10.4.8 or later (x86 only)
  • Linux (tested on Linux Ubuntu Dapper Drake)

Supported Development Environments

Note: If JDK is already installed on your development computer, please take a moment to make sure that it meets the version requirements listed above. In particular, note that some Linux distributions may include JDK 1.4 or Gnu Compiler for Java, both of which are not supported for Android development.

Installing the SDK

After downloading the SDK, unpack the .zip archive to a suitable location on your machine. By default, the SDK files are unpacked into a directory named android_sdk_<platform>_<release>_<build>. The directory contains the subdirectories tools/, samples/, and others.

Make a note of the name and location of the unpacked SDK directory on your system — you will need to refer to the SDK directory later, when setting up the Android plugin or using SDK tools.

Optionally, you can add the path to the SDK tools directory to your path. As mentioned above, the tools/ directory is located in the SDK directory.

  • On Linux, edit your ~/.bash_profile or ~/.bashrc file. Look for a line that sets the PATH environment variable and add the full path to the tools/ directory to it. If you don't see a line setting the path, you can add one:
      export PATH=${PATH}:<your_sdk_dir>/tools
  • On a Mac, look in your home directory for .bash_profile and proceed as for Linux. You can create the .bash_profile, if you haven't already set one up on your machine.
  • On Windows, right click on My Computer, and select Properties. Under the Advanced tab, hit the Environment Variables button, and in the dialog that comes up, double-click on Path under System Variables. Add the full path to the tools/ directory to the path.

Adding tools to your path lets you run Android Debug Bridge (adb) and the other command line tools without needing to supply the full path to the tools directory. Note that, if you update your SDK, you should remember to update your PATH settings to point to the new location, if different.

Installing the Eclipse Plugin (ADT)

Tips for downloading ADT

If you are having trouble downloading the ADT plugin after following the steps listed at left, here are some suggestions:

  • In Step 4, try changing the remote update site URL to use http, rather than https.
  • If you are behind a firewall (such as a corporate firewall), make sure that you have properly configured your proxy settings in Eclipse. In Eclipse 3.3, you can configure proxy information from the main Eclipse menu in Window > Preferences > General > Network Connections. In Eclipse 3.2, use Window > Preferences > Install/Update.

If you are still unable to use Eclipse to download the ADT plugin, follow these steps to download and install the plugin from your computer:

  1. Download the ADT zip file
  2. Unpack the zip file in its own folder
  3. Follow steps 1 and 2 in the default install instructions (on the left)
  4. Press New Local Site...
  5. In the resulting dialog box, select the folder where you unpacked the zip file
  6. Follow steps 5 through 11 in the default install instructions (on the left) to complete the installation

Note that to update your plugin, you will have to follow these steps again instead of the default update instructions.

If you will be using the Eclipse IDE as your environment for developing Android applications, you can install a custom plugin called Android Development Tools (ADT), which adds integrated support for Android projects and tools. The ADT plugin includes a variety of powerful extensions that make creating, running, and debugging Android applications faster and easier.

If you will not be using the Eclipse IDE, you do not need to download or install the ADT plugin.

To download and install the ADT plugin, follow the steps below.

  1. Start Eclipse, then select Help > Software Updates > Find and Install....
  2. In the dialog that appears, select Search for new features to install and press Next.
  3. Press New Remote Site.
  4. In the resulting dialog box, enter a name for the remote site (e.g. Android Plugin) and enter this as its URL: 
    https://dl-ssl.google.com/android/eclipse/
    Press OK.
  5. You should now see the new site added to the search list (and checked). Press Finish.
  6. In the subsequent Search Results dialog box, select the checkbox for Android Plugin > Developer Tools. This will check both features: "Android Developer Tools", and "Android Editors". The Android Editors feature is optional, but recommended. If you choose to install it, you need the WST plugin mentioned earlier in this page.

    Now press Next.

  7. Read the license agreement and then select Accept terms of the license agreement, if appropriate. Press Next.
  8. Press Finish.
  9. The ADT plugin is not signed; you can accept the installation anyway by pressing Install All.
  10. Restart Eclipse.
  11. After restart, update your Eclipse preferences to point to the SDK directory:
    1. Select Window > Preferences... to open the Preferences panel. (Mac OS X: Eclipse > Preferences)
    2. Select Android from the left panel.
    3. For the SDK Location in the main panel, press Browse... and locate the SDK directory.
    4. Press Apply, then OK.

Updating the ADT Plugin

In some cases, a new ADT plugin may become available for your existing version of the SDK. You can use the steps below to update the ADT plugin from inside Eclipse.

  1. Select Help > Software Updates > Find and Install....
  2. Select Search for updates of the currently installed features and press Finish.
  3. If any update for ADT is available, select and install.

Alternatively,

  1. Select Help > Software Updates > Manage Configuration.
  2. Navigate down the tree and select Android Development Tools <version>
  3. Select Scan for Updates under Available Tasks.

Developing Android Applications on Eclipse

To begin developing Android applications in the Eclipse IDE, you first create an Android project and then set up a launch configuration. After that, you can write, run, and debug your application.

The sections below provide instructions assuming that you have installed the ADT plugin in your Eclipse environment. If you haven't installed the ADT plugin, you should do that before using the instructions below. See the Installing the Eclipse Plugin (ADT) for more information.

Creating an Android Project

The ADT plugin provides a New Project Wizard that you can use to quickly create an Eclipse project for new or existing code. To create the project, follow these steps:

  1. Select File > New > Project
  2. Select Android > Android Project, and press Next
  3. Select the contents for the project:
    • Select Create new project in workspace to start a project for new code.

      Enter the project name, the base package name, the name of a single Activity class to create as a stub .java file, and a name to use for your application.

    • Select Create project from existing source to start a project from existing code. Use this option if you want to build and run any of the sample applications included with the SDK. The sample applications are located in the samples/ directory in the SDK.

      Browse to the directory containing the existing source code and click OK. If the directory contains a valid Android manifest file, the ADT plugin fills in the package, activity, and application names for you.

  4. Press Finish.

The ADT plugin creates the these folders and files for you as appropriate for the type of project:

  • src/A folder that includes your stub .java Activity file.
  • res/A folder for your resources.
  • AndroidManifest.xmlThe manifest for your project.

    Creating a Launch Configuration

    Before you can run and debug your application in Eclipse, you must create a launch configuration for it. A launch configuration specifies the project to launch, the Activity to start, the emulator options to use, and so on.

    To create a launch configuration for the application, follow these steps:

    1. Select Run > Open Run Dialog... or Run > Open Debug Dialog... as appropriate.
    2. In the project type list on the left, right-click Android Application and select New.
    3. Enter a name for your configuration.
    4. On the Android tab, browse for the project and Activity to start.
    5. On the Target tab, set the desired screen and network properties, as well as any other emulator startup options.
    6. You can set additional options on the Common tab as desired.
    7. Press Apply to save the launch configuration, or press Run or Debug (as appropriate).

    Running and Debugging an Application

    Once you've set up the project and launch configuration for your application, you can run or debug it as described below.

    From the Eclipse main menu, select Run > Run or Run > Debug as appropriate, to run or debug the active launch configuration.

    Note that the active launch configuration is the one most recently selected in the Run configuration manager. It does not necessarily correspond to the application that is selected in the Eclipse Navigation pane (if any).

    To set or change the active launch configuration, use the Run configuration manager, which you can access through Run > Open Run Dialog... or Run > Open Debug Dialog....

    Running or debugging the application triggers these actions:

    • Starts the emulator, if it is not already running.
    • Compiles the project, if there have been changes since the last build, and installs the application on the emulator.
    • Run starts the application.
    • Debug starts the application in "Wait for debugger" mode, then opens the Debug perspective and attaches the Eclipse Java debugger to the application.

    Developing Android Applications with Other IDEs and Tools

    The recommended way to develop an Android application is to use Eclipse with the Android plugin. This plugin provides editing, building, and debugging functionality integrated right into the IDE. However, the SDK includes tools to enable you to develop with other IDEs, including intelliJ (or if you'd rather use Eclipse without the plugin).

    Creating an Android Project

    The Android SDK includes activityCreator, a program that generates a number of stub files for your project, as well as a build file. You can use the program to create an Android project for new code or from existing code, such as the sample applications included in the SDK. For Linux and Mac, the SDK provides activityCreator.py, a Python script, and for Windows, activityCreator.bat, a batch script. Regardless of platform, you can use activityCreator in the same way.

    To run activityCreator and create an Android project, follow these steps:

    1. In the command line, change to the tools/ directory of the SDK and create a new directory for your project files. If you are creating a project from existing code, change to the root folder of your application instead.

    2. Run activityCreator. In the command, you must specify a fully-qualified class name as an argument. If you are creating a project for new code, the class represents the name of a stub class that the script will create. If you are creating a project from existing code, you must specify the name of one Activity class in the package. Command options for the script include:

      • --out <folder> which sets the output directory. By default, the output directory is the current directory. If you created a new directory for your project files, use this option to point to it.
      • --ide intellij, which generates IntelliJ IDEA project files in the newly created project

    Here's an example:

    ~/android_linux_sdk/tools $ ./activityCreator.py --out myproject your.package.name.ActivityName
package: your.package.name
out_dir: myproject
activity_name: ActivityName
~/android_linux_sdk/tools $

    The activityCreator script generates the following files and directories (but will not overwrite existing ones):

    • AndroidManifest.xml The application manifest file, synced to the specified Activity class for the project.
    • build.xml An Ant file that you can use to build/package the application.
    • src/your/package/name/ActivityName.javaThe Activity class you specified on input.
    • your_activity.iml, your_activity.ipr, your_activity.iws [only with the -ide intelliJ flag] intelliJ project files.
    • res/ A directory to hold resources.
    • src/ The source directory.
    • bin/ The output directory for the build script.

    You can now move your folder wherever you want for development, but keep in mind that you'll have to use the adb program in the tools/ folder to send files to the emulator, so you'll need access between your solution and the tools/ folder.

    Also, you should refrain from moving the location of the SDK directory, since this will break the build scripts (they will need to be manually updated to reflect the new SDK location before they will work again).

    Building an Android Application

    Use the Ant build.xml file generated by activityCreator to build your application.

    1. If you don't have it, you can obtain Ant from the Apache Ant home page. Install it and make sure it is on your executable path.
    2. Before calling Ant, you need to declare the JAVA_HOME environment variable to specify the path to where the JDK is installed.

      Note: When installing JDK on Windows, the default is to install in the "Program Files" directory. This location will cause ant to fail, because of the space. To fix the problem, you can specify the JAVA_HOME variable like this: set JAVA_HOME=c:\Prora~1\Java\<jdkdir></jdkdir>. The easiest solution, however, is to install JDK in a non-space directory, for example: c:\java\jdk1.6.0_02.

    3. If you have not done so already, follow the instructions for Creating a New Project above to set up the project.
    4. You can now run the Ant build file by simply typing ant in the same folder as the build.xml file for your project. Each time you change a source file or resource, you should run ant again and it will package up the latest version of the application for you to deploy.

    Running an Android Application

    To run a compiled application, you will upload the .apk file to the /data/app/ directory in the emulator using the adb tool as described here:

    1. Start the emulator (run <your_sdk_dir>/tools/emulator from the command line)
    2. On the emulator, navigate to the home screen (it is best not to have that application running when you reinstall it on the emulator; press the Home key to navigate away from that application).
    3. Run adb install myproject/bin/<appname>.apk to upload the executable. So, for example, to install the Lunar Lander sample, navigate in the command line to <your_sdk_dir>/sample/LunarLander and type ../../tools/adbinstallbin/LunarLander.apk
    4. In the emulator, open the list of available applications, and scroll down to select and start your application.

    Note: When you install an Activity for the first time, you might have to restart the emulator before it shows up in the application launcher, or other applications can call it. This is because the package manager usually only examines manifests completely on emulator startup.

    Attaching a Debugger to Your Application

    This section describes how to display debug information on the screen (such as CPU usage), as well as how to hook up your IDE to debug running applications on the emulator.

    Attaching a debugger is automated using the Eclipse plugin, but you can configure other IDEs to listen on a debugging port to receive debugging information.

    1. Start the Dalvik Debug Monitor Server (DDMS) tool , which acts as a port forwarding service between your IDE and the emulator.
    2. Set optional debugging configurations on your emulator, such as blocking application startup for an activity until a debugger is attached. Note that many of these debugging options can be used without DDMS, such as displaying CPU usage or screen refresh rate on the emulator.
    3. Configure your IDE to attach to port 8700 for debugging. We include information on how to set up Eclipse to debug your project.

    Configuring your IDE to attach to the debugging port

    DDMS will assign a specific debugging port to every virtual machine that it finds on the emulator. You must either attach your IDE to that port (listed on the Info tab for that VM), or you can use a default port 8700 to connect to whatever application is currently selected on the list of discovered virtual machines.

    Your IDE should attach to your application running on the emulator, showing you its threads and allowing you to suspend them, inspect their state, and set breakpoints. If you selected "Wait for debugger" in the Development settings panel the application will run when Eclipse connects, so you will need to set any breakpoints you want before connecting.

    Changing either the application being debugged or the "Wait for debugger" option causes the system to kill the selected application if it is currently running. You can use this to kill your application if it is in a bad state by simply going to the settings and toggling the checkbox.

    Debugging

    Android has a fairly extensive set of tools to help you debug your programs:

    • DDMS - A graphical program that supports port forwarding (so you can set up breakpoints in your code in your IDE), screen captures on the emulator, thread and stack information, and many other features. You can also run logcat to retrieve your Log messages. See the linked topic for more information.
    • logcat - Dumps a log of system messages. The messages include a stack trace when the emulator throws an error, as well as Log messages. To run logcat, see the linked topic. 
      ...
I/MemoryDealer( 763): MemoryDealer (this=0x54bda0): Creating 2621440 bytes heap at 0x438db000
I/Logger( 1858): getView() requesting item number 0
I/Logger( 1858): getView() requesting item number 1
I/Logger( 1858): getView() requesting item number 2
D/ActivityManager( 763): Stopping: HistoryRecord{409dbb20 com.google.android.home.AllApps}
...

    • Android Log- A logging class to print out messages to a log file on the emulator. You can read messages in real time if you run logcat on DDMS (covered next). Add a few logging method calls to your code.

      To use the Log class, you just call Log.v() (verbose), Log.d() (debug), Log.i() (information), Log.w() (warning) or Log.e (error) depending on the importance you wish to assign the log message.

      Log.i("MyActivity", "MyClass.getView() — Requesting item number " + position)

      You can use logcat to read these messages

    • Traceview - Android can save a log of method calls and times to a logging file that you can view in a graphical reader called Traceview. See the linked topic for more information.
    • Eclipse plugin - The Eclipse Android plugin incorporates a number of these tools (ADB, DDMS, logcat output, and other functionality). See the linked topic for more information.
    • Debug and Test Device Settings - Android exposes several settings that expose useful information such as CPU usage and frame rate. See Debug and Test Settings on the Emulator below.

    Also, see the Troubleshooting section of the doc to figure out why your application isn't appearing on the emulator, or why it's not starting.

    Debug and Test Settings on the Device

    Android lets you set a number of settings that will make it easier to test and debug your applications. To get to the development settings page on the emulator, go to Dev Tools > Development Settings. This will open the development settings page with the following options (among others):

    • Debug appSelects the application that will be debugged. You do not need to set this to attach a debugger, but setting this value has two effects:
      • It will prevent Android from throwing an error if you pause on a breakpoint for a long time while debugging.
      • It will enable you to select the Wait for Debugger option to pause application startup until your debugger attaches (described next).
    • Wait for debugger Blocks the selected application from loading until a debugger attaches. This way you can set a breakpoint in onCreate(), which is important to debug the startup process of an Activity. When you change this option, any currently running instances of the selected application will be killed. In order to check this box, you must have selected a debug application as described in the previous option. You can do the same thing by adding waitForDebugger() to your code.
    • Immediately destroy activitiesTells the system to destroy an activity as soon as it is stopped (as if Android had to reclaim memory). This is very useful for testing the onFreeze(Bundle) / onCreate(android.os.Bundle) code path, which would otherwise be difficult to force. Choosing this option will probably reveal a number of problems in your application due to not saving state.
    • Show screen updates Flashes a momentary pink rectangle on any screen sections that are being redrawn. This is very useful for discovering unnecessary screen drawing.
    • Show CPU usageDisplays CPU meters at the top of the screen, showing how much the CPU is being used. The top red bar shows overall CPU usage, and the green bar underneath it shows the CPU time spent in compositing the screen. Note: You cannot turn this feature off once it is on, without restarting the emulator.
    • Show backgroundDisplays a background pattern when no activity screens are visible. This typically does not happen, but can happen during debugging.

    These settings will be remembered across emulator restarts.

    Top Debugging Tips

    <!-- <ul> <li><a href="#stackdump">Quick stack dump</a></li> <li><a href="#displayinfo">Displaying useful info on the emulator screen </a></li> <li><a href="#dumpstate">Getting system state information from the emulator (dumpstate)</a></li> <li><a href="#dumpsys">Getting application state information from the emulator (dumpsys)</a></li> <li><a href="#radioinfo">Getting wireless connectivity information</a></li> <li><a href="#loggingdata">Logging Trace Data</a></li> <li><a href="#logradio">Logging Radio Data </a></li> <li><a href="#adb">Running adb</a></li> <li><a href="#screencaps">Getting screen captures from the emulator</a></li> <li><a href="#debughelpers">Using debug helper classes</a></li> </ul> -->
    Quick stack dump
    To obtain a stack dump from emulator, you can log in with adb shell, use "ps" to find the process you want, and then "kill -3 ". The stack trace appears in the log file.
    Displaying useful info on the emulator screen
    The device can display useful information such as CPU usage or highlights around redrawn areas. Turn these features on and off in the developer settings window as described in Setting debug and test configurations on the emulator.
    Getting system state information from the emulator (dumpstate)
    You can access dumpstate information from the Dalvik Debug Monitor Service tool. See dumpsys and dumpstate on the adb topic page.
    Getting application state information from the emulator (dumpsys)
    You can access dumpsys information from the Dalvik Debug Monitor Service tool. See dumpsys and dumpstate on the adb topic page.
    Getting wireless connectivity information
    You can get information about wireless connectivity using the Dalvik Debug Monitor Service tool. From the Device menu, select "Dump radio state".
    Logging Trace Data
    You can log method calls and other tracing data in an activity by calling android.os.Debug.startMethodTracing(). See Running the Traceview Debugging Program for details.
    Logging Radio Data
    By default, radio information is not logged to the system (it is a lot of data). However, you can enable radio logging using the following commands: 
    adb shell
logcat -b radio
    Running adb
    Android ships with a tool called adb that provides various capabilities, including moving and syncing files to the emulator, forwarding ports, and running a UNIX shell on the emulator. See Using adb for details.
    Getting screen captures from the emulator
    Dalvik Debug Monitor Server (DDMS) can capture screenshots from the emulator.
    Using debugging helper classes
    Android provides debug helper classes such as util.Log and Debug for your convenience.

    Building and Installing an Android Application

    Android requires custom build tools to be able to properly build the resource files and other parts of an Android application. Because of this, you must have a specialized build environment for your application.

    Custom Android compilation steps include compiling the XML and other resource files, and creating the proper output format. A compiled Android application is an .apk file, which is a compressed file containing .dex files, resource files, raw data files, and other files. You can create a properly structured Android project either from scratch, or from existing source files.

    Android does not currently support development of third party applications in native code (C/C++).

    The recommended way to develop an Android application is to use Eclipse with the Android plugin, which provides support for building, running, and debugging Android applications.

    If you have another IDE, Android provides tools for other IDEs to build and debug Android applications, but they are not as integrated.

    Removing an Android Application

    To remove an application that you have installed on the emulator, you will need to run adb and delete the .apk file you sent to the emulator when you installed it. Use adb shell to drop into a shell on the device as described in the linked topic, navigate to data/app/, and then remove the file using rm your_app.apk.

    Eclipse Tips

    Executing arbitrary Java expressions in Eclipse

    You can execute arbitrary code when paused at a breakpoint in Eclipse. For example, when in a function with a String argument called "zip", you can get information about packages and call class methods. You can also invoke arbitrary static methods: for example, entering android.os.Debug.startMethodTracing() will start dmTrace.

    Open a code execution window, select Window>Show View>Display from the main menu to open the Display window, a simple text editor. Type your expression, highlight the text, and click the 'J' icon (or CTRL + SHIFT + D) to run your code. The code runs in the context of the selected thread, which must be stopped at a breakpoint or single-step point. (If you suspend the thread manually, you have to single-step once; this doesn't work if the thread is in Object.wait().)

    If you are currently paused on a breakpoint, you can simply highlight and execute a piece of source code by pressing CTRL + SHIFT + D.

    You can highlight a block of text within the same scope by pressing ALT +SHIFT + UP ARROW to select larger and larger enclosing blocks, or DOWN ARROW to select smaller blocks.

    Here are a few sample inputs and responses in Eclipse using the Display window.

    Input Response
    zip (java.lang.String) /work/device/out/linux-x86-debug/android/app/android_sdk.zip
    zip.endsWith(".zip") (boolean) true
    zip.endsWith(".jar") (boolean) false

    You can also execute arbitrary code when not debugging by using a scrapbook page. Search the Eclipse documentation for "scrapbook".

    Running DDMS Manually

    Although the recommended way to debug is to use the ADT plugin, you can manually run DDMS and configure Eclipse to debug on port 8700. (Note: Be sure that you have first started DDMS).

    ——————————————————————————————————————————————

    Hello, Android!

    First impressions matter, and as a developer you know that the first impression you get of a development framework is how easy it is to write "Hello, World!" Well, in Android, it's pretty easy. Here's how it looks:

    The sections below spell it all out in detail.

    Let's jump in!

    Create the Project

    Creating the project is as simple as can be. An Eclipse plugin is available making Android development a snap.

    You'll need to have a development computer with the Eclipse IDE installed (see System and Software Requirements), and you'll need to install the Android Eclipse Plugin (ADT). Once you have those ready, come back here.

    First, here's a high-level summary of how to build "Hello, World!":

    1. Create a new "Android Project" via the File > New > Project menu.
    2. Fill out the project details in the New Android Project dialog.
    3. Edit the auto-generated source code template to display some output.

    That's it! Next, let's go through each step above in detail.

    1. Create a new Android Project

      From Eclipse, select the File > New > Project menu item. If the Android Plugin for Eclipse has been successfully installed, the resulting dialog should have a folder labeled "Android" which should contain a single entry: "Android Project".

      Once you've selected "Android Project", click the Next button.

    2. Fill out the project details

      The next screen allows you to enter the relevant details for your project. Here's an example:

      Here's what each field on this screen means:

      Project Name This is the name of the directory or folder on your computer that you want to contain the project.
      Package Name This is the package namespace (following the same rules as for packages in the Java programming language) that you want all your source code to reside under. This also sets the package name under which the stub Activity will be generated.

      The package name you use in your application must be unique across all packages installed on the system; for this reason, it's very important to use a standard domain-style package for your applications. In the example above, we used the package domain "com.android"; you should use a different one appropriate to your organization.
      Activity Name This is the name for the class stub that will be generated by the plugin. This will be a subclass of Android's Activity class. An Activity is simply a class that can run and do work. It can create a UI if it chooses, but it doesn't need to.
      Application Name This is the human-readable title for your application.

      The checkbox for toggling "Use default location" allows you to change the location on disk where the project's files will be generated and stored.

    3. Edit the auto-generated source code

      After the plugin runs, you'll have a class named HelloAndroid that looks like this:

      public class HelloAndroid extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        setContentView(R.layout.main);
    }
}

      The next step is to start modifying it!

    Construct the UI

    Once you've got the project set up, the obvious next step is to get some text up there on the screen. Here's the finished product — next we'll dissect it line by line:

    package com.android.hello;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class HelloAndroid extends Activity {
   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle icicle) {
       super.onCreate(icicle);
       TextView tv = new TextView(this);
       tv.setText("Hello, Android");
       setContentView(tv);
   }
}

    In Android, user interfaces are composed of hierarchies of classes called Views. A View is simply a drawable object, such as a radio button, an animation, or (in our case) a text label. The specific name for the View subclass that handles text is simply TextView.

    Here's how you construct a TextView:

    TextView tv = new TextView(this);

    The argument to TextView's constructor is an Android Context instance. The Context is simply a handle to the system; it provides services like resolving resources, obtaining access to databases and preferences, and so on. The Activity class inherits from Context. Since our HelloAndroid class is a subclass of Activity, it is also a Context, and so we can pass the 'this' reference to the TextView.

    Once we've constructed the TextView, we need to tell it what to display:

    tv.setText("Hello, Android");

    Nothing too surprising there.

    At this point, we've constructed a TextView and told it what text to display. The final step is to connect this TextView with the on-screen display, like so:

    setContentView(tv);

    The setContentView() method on Activity indicates to the system which View should be associated with the Activity's UI. If an Activity doesn't call this method, no UI is present at all and the system will display a blank screen. For our purposes, all we want is to display some text, so we pass it the TextView we just created.

    There it is — "Hello, World" in Android! The next step, of course, is to see it running.

    Run the Code: Hello, Android

    The Eclipse plugin makes it very easy to

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