Android中的adapter

Adapter介绍

Android是完全遵循MVC模式设计的框架,Activity是Controller,layout是View
因为layout五花八门,很多数据都不能直接绑定上去,所以Android引入了Adapter这个机制作为复杂数据的展示的转换载体,所以各种Adapter只不过是转换的方式和能力不一样而已。
几种常用的Adapter:



其中BaseAdapter的直接子类：
ArrayAdapter<T>, CursorAdapter, SimpleAdapter

BaseAdapter的间接子类：
ResourceCursorAdapter, SimpleCursorAdapter

Adapter是将数据绑定到UI界面上的桥接类。Adapter负责创建显示每个项目的子View和提供对下层数据的访问。
  
在多数情况下，你不需要白手创建自己的Adapter。Android提供了一系列Adapter来将数据绑定到UI Widget上。

因为Android负责提供数据和选择用于显示每个项目的View，所以Adapter能快速地修改要绑定的控件的外观和功能。下面的列表显示了两个最有用和最通用的本地Adapter：

❑ ArrayAdapter
ArrayAdapter是一个绑定View到一组对象的通用类。默认情况下，ArrayAdapter绑定每个对象的toString值到在layout中预先定义的TextView控件上。可变通的，构造函数允许你使用更加复杂的layout或者通过重写getView方法来扩展类从而使用TextView的替代物（如ImageView或嵌套的layout）。

❑ SimpleCursorAdapter
SimpleCursorAdapter绑定View到Content Provider查询返回的游标上。指定一个XML layout定义，然后将数据集中的每一列的值绑定到layout中的一个View上。

下面演示一下SimpleAdapter的用法：

package com.wt.app;

import java.util.ArrayList;
import java.util.HashMap;

import android.app.Activity;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.MenuItem;
import android.view.View;
import android.view.ContextMenu.ContextMenuInfo;
import android.view.View.OnCreateContextMenuListener;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.AdapterView.OnItemClickListener;

public class App extends Activity {
	@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        //绑定Layout里面的ListView
        ListView list = (ListView) findViewById(R.id.ListView01);
        
        //生成动态数组，加入数据
        ArrayList<HashMap<String, Object>> listItem = new ArrayList<HashMap<String, Object>>();
        int[] images=new int[]{android.R.drawable.ic_menu_add,android.R.drawable.ic_menu_delete,android.R.drawable.ic_menu_edit,android.R.drawable.ic_menu_view};
        for(int i=0;i<4;i++)
        {
        	HashMap<String, Object> map = new HashMap<String, Object>();
        	map.put("itemImage", images[i]);//图像资源的ID
        	map.put("itemTitle", "Title "+i);
        	map.put("itemText", "this is Text "+i);
        	listItem.add(map);
        }
        //生成适配器的Item和动态数组对应的元素
        SimpleAdapter listItemAdapter = new SimpleAdapter(this,listItem,//数据源 
            R.layout.row,//ListItem的XML实现
            //动态数组与ImageItem对应的子项        
            new String[] {"itemImage","itemTitle", "itemText"}, 
            //ImageItem的XML文件里面的一个ImageView,两个TextView ID
            new int[] {R.id.itemImage,R.id.itemTitle,R.id.itemText}
        );
       
        //添加并且显示
        list.setAdapter(listItemAdapter);
        //添加点击
        list.setOnItemClickListener(new OnItemClickListener() {

			public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
					long arg3) {
				setTitle("点击第"+arg2+"个项目");
			}
		});
        
      //添加长按点击
        list.setOnCreateContextMenuListener(new OnCreateContextMenuListener() {
			
			public void onCreateContextMenu(ContextMenu menu, View v,ContextMenuInfo menuInfo) {
				menu.setHeaderTitle("长按菜单-ContextMenu");   
				menu.add(0, 0, 0, "弹出长按菜单0");
				menu.add(0, 1, 0, "弹出长按菜单1");   
			}
		}); 
    }
	
	//长按菜单响应函数
	@Override
	public boolean onContextItemSelected(MenuItem item) {
		setTitle("点击了长按菜单里面的第"+item.getItemId()+"个项目"); 
		return super.onContextItemSelected(item);
	}
}

整体布局文件，一个简单的ListView：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
	<ListView android:layout_width="wrap_content"   
          android:layout_height="wrap_content"   
          android:id="@+id/ListView01"  
    />  
</LinearLayout>

ListView中每行（row）怎么显示的布局文件：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 
	android:id="@+id/RelativeLayout01" 
	android:layout_width="fill_parent" 
	xmlns:android="http://schemas.android.com/apk/res/android" 
	android:layout_height="wrap_content" 
	android:paddingTop="4dip" 
	android:paddingBottom="4dip" 
	android:paddingLeft="12dip"
	android:paddingRight="12dip">
<ImageView 
	android:paddingTop="12dip"
	android:layout_alignParentRight="true"
	android:layout_width="wrap_content" 
	android:layout_height="wrap_content" 
	android:id="@+id/itemImage"
	/> 
<TextView 
    android:layout_height="wrap_content" 
    android:textSize="20dip" 
    android:layout_width="fill_parent" 
    android:id="@+id/itemTitle"
    />
<TextView 
	android:layout_height="wrap_content" 
	android:layout_width="fill_parent" 
	android:layout_below="@+id/itemTitle" 
	android:id="@+id/itemText"
	/>
</RelativeLayout>

下面演示了BaseExpandableListAdapter的用法：

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.apis.view;

import android.app.ExpandableListActivity;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.Gravity;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.view.ContextMenu.ContextMenuInfo;
import android.widget.AbsListView;
import android.widget.BaseExpandableListAdapter;
import android.widget.ExpandableListAdapter;
import android.widget.ExpandableListView;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.ExpandableListView.ExpandableListContextMenuInfo;

import com.example.android.apis.R;

/**
 * Demonstrates expandable lists using a custom {@link ExpandableListAdapter}
 * from {@link BaseExpandableListAdapter}.
 */
public class ExpandableList1 extends ExpandableListActivity {

    ExpandableListAdapter mAdapter;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Set up our adapter
        mAdapter = new MyExpandableListAdapter();
        setListAdapter(mAdapter);
        registerForContextMenu(getExpandableListView());
    }

    @Override
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) {
        menu.setHeaderTitle("Sample menu");
        menu.add(0, 0, 0, R.string.expandable_list_sample_action);
    }
    
    @Override
    public boolean onContextItemSelected(MenuItem item) {
        ExpandableListContextMenuInfo info = (ExpandableListContextMenuInfo) item.getMenuInfo();

        String title = ((TextView) info.targetView).getText().toString();
        
        int type = ExpandableListView.getPackedPositionType(info.packedPosition);
        if (type == ExpandableListView.PACKED_POSITION_TYPE_CHILD) {
            int groupPos = ExpandableListView.getPackedPositionGroup(info.packedPosition); 
            int childPos = ExpandableListView.getPackedPositionChild(info.packedPosition); 
            Toast.makeText(this, title + ": Child " + childPos + " clicked in group " + groupPos,
                    Toast.LENGTH_SHORT).show();
            return true;
        } else if (type == ExpandableListView.PACKED_POSITION_TYPE_GROUP) {
            int groupPos = ExpandableListView.getPackedPositionGroup(info.packedPosition); 
            Toast.makeText(this, title + ": Group " + groupPos + " clicked", Toast.LENGTH_SHORT).show();
            return true;
        }
        
        return false;
    }

    /**
     * A simple adapter which maintains an ArrayList of photo resource Ids. 
     * Each photo is displayed as an image. This adapter supports clearing the
     * list of photos and adding a new photo.
     *
     */
    public class MyExpandableListAdapter extends BaseExpandableListAdapter {
        // Sample data set.  children[i] contains the children (String[]) for groups[i].
        private String[] groups = { "People Names", "Dog Names", "Cat Names", "Fish Names" };
        private String[][] children = {
                { "Arnold", "Barry", "Chuck", "David" },
                { "Ace", "Bandit", "Cha-Cha", "Deuce" },
                { "Fluffy", "Snuggles" },
                { "Goldy", "Bubbles" }
        };
        
        public Object getChild(int groupPosition, int childPosition) {
            return children[groupPosition][childPosition];
        }

        public long getChildId(int groupPosition, int childPosition) {
            return childPosition;
        }

        public int getChildrenCount(int groupPosition) {
            return children[groupPosition].length;
        }

        public TextView getGenericView() {
            // Layout parameters for the ExpandableListView
            AbsListView.LayoutParams lp = new AbsListView.LayoutParams(
                    ViewGroup.LayoutParams.MATCH_PARENT, 64);

            TextView textView = new TextView(ExpandableList1.this);
            textView.setLayoutParams(lp);
            // Center the text vertically
            textView.setGravity(Gravity.CENTER_VERTICAL | Gravity.LEFT);
            // Set the text starting position
            textView.setPadding(36, 0, 0, 0);
            return textView;
        }
        
        public View getChildView(int groupPosition, int childPosition, boolean isLastChild,
                View convertView, ViewGroup parent) {
            TextView textView = getGenericView();
            textView.setText(getChild(groupPosition, childPosition).toString());
            return textView;
        }

        public Object getGroup(int groupPosition) {
            return groups[groupPosition];
        }

        public int getGroupCount() {
            return groups.length;
        }

        public long getGroupId(int groupPosition) {
            return groupPosition;
        }

        public View getGroupView(int groupPosition, boolean isExpanded, View convertView,
                ViewGroup parent) {
            TextView textView = getGenericView();
            textView.setText(getGroup(groupPosition).toString());
            return textView;
        }

        public boolean isChildSelectable(int groupPosition, int childPosition) {
            return true;
        }

        public boolean hasStableIds() {
            return true;
        }

    }
}

SimpleCursorTreeAdapter用法：

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.apis.view;

import android.app.ExpandableListActivity;
import android.content.ContentUris;
import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.Contacts.People;
import android.widget.ExpandableListAdapter;
import android.widget.SimpleCursorTreeAdapter;


/**
 * Demonstrates expandable lists backed by Cursors
 */
public class ExpandableList2 extends ExpandableListActivity {
    private int mGroupIdColumnIndex; 
    
    private String mPhoneNumberProjection[] = new String[] {
            People.Phones._ID, People.Phones.NUMBER
    };

    
    private ExpandableListAdapter mAdapter;
    

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Query for people
        Cursor groupCursor = managedQuery(People.CONTENT_URI,
                new String[] {People._ID, People.NAME}, null, null, null);

        // Cache the ID column index
        mGroupIdColumnIndex = groupCursor.getColumnIndexOrThrow(People._ID);

        // Set up our adapter
        mAdapter = new MyExpandableListAdapter(groupCursor,
                this,
                android.R.layout.simple_expandable_list_item_1,
                android.R.layout.simple_expandable_list_item_1,
                new String[] {People.NAME}, // Name for group layouts
                new int[] {android.R.id.text1},
                new String[] {People.NUMBER}, // Number for child layouts
                new int[] {android.R.id.text1});
        setListAdapter(mAdapter);
    }

    public class MyExpandableListAdapter extends SimpleCursorTreeAdapter {

        public MyExpandableListAdapter(Cursor cursor, Context context, int groupLayout,
                int childLayout, String[] groupFrom, int[] groupTo, String[] childrenFrom,
                int[] childrenTo) {
            super(context, cursor, groupLayout, groupFrom, groupTo, childLayout, childrenFrom,
                    childrenTo);
        }

        @Override
        protected Cursor getChildrenCursor(Cursor groupCursor) {
            // Given the group, we return a cursor for all the children within that group 

            // Return a cursor that points to this contact's phone numbers
            Uri.Builder builder = People.CONTENT_URI.buildUpon();
            ContentUris.appendId(builder, groupCursor.getLong(mGroupIdColumnIndex));
            builder.appendEncodedPath(People.Phones.CONTENT_DIRECTORY);
            Uri phoneNumbersUri = builder.build();

            // The returned Cursor MUST be managed by us, so we use Activity's helper
            // functionality to manage it for us.
            return managedQuery(phoneNumbersUri, mPhoneNumberProjection, null, null, null);
        }

    }
}