Android 四大组件之 ContentProvider

简介

简而言之，ContentProvider 向别的应用程序提供数据(联系人这个应用程序提供了 它的 ContentProvider)，ContentResolver 从别的应用程序(已提供ContentProvider)获取、修改、添加数据(我们可以通过ContentResolver 来操纵联系人中的数据)。

说明

既然是四大组件之一，那么创建步骤基本相同

1: 自定义 ContentProvider

2: 注册

3: 使用

1自定义ContentProvider

MyProvider.java

package com.myprovider;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
public class MyProvider extends ContentProvider{
    DatabaseHelper dbhelper;
    SQLiteDatabase db;
    
    UriMatcher UMatcher=new UriMatcher(UriMatcher.NO_MATCH);
    
    @Override
    public boolean onCreate() {
        // TODO 自动生成的方法存根
        dbhelper=new DatabaseHelper(getContext(), "michael", null, 1);
        
        UMatcher.addURI("com.michael", "michael", 1);
        UMatcher.addURI("com.michael", "michael/#", 2);
        db=dbhelper.getWritableDatabase();
        return true;
    }
    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
        // TODO 自动生成的方法存根
        Cursor cursor;
        
        switch(UMatcher.match(uri))
        {
        case 1:
            cursor= db.query("michael", projection, selection, selectionArgs, null, null, sortOrder);
            break;
        case 2:
            long id=ContentUris.parseId(uri);
            String myselection="_id="+id;
            
            if(selection!=null)
                myselection +=selection;    
            
            cursor =db.query("michael", projection, myselection, selectionArgs, null, null, sortOrder);
            break;
        default:
            //非法的参数异常
            throw new IllegalArgumentException("unknow uri" + uri.toString());
        }
        return cursor;
    }
    @Override
    public String getType(Uri uri) {
        // TODO 自动生成的方法存根
        return null;
    }
    @Override
    public Uri insert(Uri uri, ContentValues values) {
        // TODO 自动生成的方法存根
        long id =db.insert("michael", "username", values);
        return ContentUris.withAppendedId(uri, id);
    }
    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        // TODO 自动生成的方法存根
        int num;
        switch(UMatcher.match(uri))
        {
        case 1:
            num=db.delete("michael", selection, selectionArgs);
            break;
        case 2:
            long id=ContentUris.parseId(uri);
            String myselection="_id="+id;
            
            if(selection!=null)
                myselection +=selection;
            
            num= db.delete("michael", myselection, selectionArgs);
            break;
        default:
            //非法的参数异常
            throw new IllegalArgumentException("unknow uri" + uri.toString());
        }
        return num;
    }
    @Override
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        // TODO 自动生成的方法存根
        int num;
        
        switch(UMatcher.match(uri))
        {
        case 1:
            num=db.update("michael", values, selection, selectionArgs);
            break;
        case 2:
            long id=ContentUris.parseId(uri);
            String myselection="_id="+id;
            
            if(selection!=null)
                myselection +=selection;
            num=db.update("michael", values, myselection, selectionArgs);
            break;
        default:
            //非法的参数异常
            throw new IllegalArgumentException("unknow uri" + uri.toString());
        }
        return num;
    }
}

2封装的 SQLiteOpenHelper 用以操作数据库

DatabaseHelper.java

package com.myprovider;
import android.content.ContentValues;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseHelper extends SQLiteOpenHelper {
    public DatabaseHelper(Context context, String name, CursorFactory factory, int version) {
        super(context, name, factory, version);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        //创建数据库
        db.execSQL("create table michael(_id integer primary key autoincrement ,username text);");
        
        //初始数据
        ContentValues values=new ContentValues();
        values.put("username", "张三");
        db.insert("michael", "username", values);
        values.put("username", "李四");
        db.insert("michael", "username", values);
        values.put("username", "王五");
        db.insert("michael", "username", values);
        values.put("username", "赵六");
        db.insert("michael", "username", values);
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        //升级数据库
        db.execSQL("drop table if exists michael;");
        this.onCreate(db);
    }
}

3注册

AndroidManifest.xml

<provider
    android:name="com.myprovider.MyProvider"
    android:authorities="com.michael"
    android:exported="true"/>

4访问数据(在别的应用程序中亦同)

意思是，你新建一个项目，具备如下代码，仍然能操作访问 上述项目中的数据。 这就是 ContentProvider 的神奇之处 :)

4.1 MainActivity.java

package com.myprovider;
import android.app.Activity;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        ContentResolver resolver=this.getContentResolver();
        Uri uri=Uri.parse("content://com.michael/michael");
        ContentValues values=new ContentValues();
        values.put("username", "霸王龙");
        resolver.insert(uri, values);
        values.put("username", "巨无霸");
        resolver.insert(uri, values);
        values.put("username", "擎天柱");
        resolver.insert(uri, values);
        values.put("username", "大黄蜂");
        resolver.insert(uri, values);
        
        Cursor cursor=resolver.query(uri, new String[]{"_id","username"}, null, null, null);
        SimpleCursorAdapter adapter=new SimpleCursorAdapter(this, android.R.layout.simple_list_item_2, cursor, new String[]{"_id","username"}, new int[]{android.R.id.text1,android.R.id.text2}, 0);
    
        ListView listview=(ListView)findViewById(R.id.listview);
        listview.setAdapter(adapter);
    }
}

4.2 activity_main.xml 布局文件

<ListView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/listview"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

5效果截图

转载请注明出处，毕竟代码是一个一个敲出来的 :)