前言

ContentProvider为存储和获取数据提供统一的接口，它可以在不同的应用程序之间共享数据，本身就是适合进程间通信的。ContentProvider底层实现也是Binder，但是使用起来比AIDL要容易许多。系统也预制了很多的ContentProvider，例如通讯录，音视频等，这些操作本身就是跨进程进行通信。这篇文章主要是我们来自己实现用ContentProvider来进行进程间通信，而非介绍ContentProvider怎么使用。

1. 建立数据库，方便ContentProvider使用

我们创建数据库,并创建表”game_provider.db”，里面有两个字段分别存储游戏的名字和游戏的描述。(DbOpenHelper.java)

public class DbOpenHelper extends SQLiteOpenHelper {    private static final String DB_NAME="game_provider.db";     static final String GAME_TABLE_NAME="game";    private static final int DB_VERSION=1;    private String CREATE_GAME_TABLE="create table if not exists " + GAME_TABLE_NAME +"(_id integer primary key," + "name TEXT, "+"describe TEXT)";    public DbOpenHelper(Context context) {        super(context, DB_NAME, null, DB_VERSION);    }    @Override    public void onCreate(SQLiteDatabase db) {       db.execSQL(CREATE_GAME_TABLE);    }    @Override    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {    }}

2. 使用ContentProvider对数据库进行操作

在initProvoder方法中，我们开启线程来对数据库进行操作，删除表的所有数据，再添加数据，并实现了query和insert方法。(GameProvider.java)

import android.content.ContentProvider;import android.content.ContentValues;import android.content.Context;import android.content.UriMatcher;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.net.Uri;public class GameProvider extends ContentProvider {    public static final String AUTHORITY = "com.example.liuwangshu.mooncontentprovide.GameProvider";    public static final Uri GAME_CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/game");    private static final UriMatcher mUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);    private SQLiteDatabase mDb;    private Context mContext;    private String table;    static {        mUriMatcher.addURI(AUTHORITY, "game", 0);    }    @Override    public boolean onCreate() {        table = DbOpenHelper.GAME_TABLE_NAME;        mContext = getContext();        initProvoder();        return false;    }    private void initProvoder() {        mDb = new DbOpenHelper(mContext).getWritableDatabase();        new Thread(new Runnable() {            @Override            public void run() {                mDb.execSQL("delete from " + DbOpenHelper.GAME_TABLE_NAME);                mDb.execSQL("insert into game values(1,'九阴真经ol','最好玩的武侠网游');");            }        }).start();    }    @Override    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {        String table = DbOpenHelper.GAME_TABLE_NAME;        Cursor mCursor = mDb.query(table, projection, selection, selectionArgs, null, sortOrder, null);        return mCursor;    }    @Override    public String getType(Uri uri) {        return null;    }    @Override    public Uri insert(Uri uri, ContentValues values) {        mDb.insert(table, null, values);        mContext.getContentResolver().notifyChange(uri, null);        return null;    }    @Override    public int delete(Uri uri, String selection, String[] selectionArgs) {        return 0;    }    @Override    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {        return 0;    }}

在manifest文件中，我们要让ContentProvider运行在另一个进程

3. 在Activity中调用另一个进程的GameProvider的方法

在Activity中我们在GameProvider再插入一条数据（此前GameProvider初始化时已经插入了一条数据），然后调用GameProvider的query方法来查询数据库中有几条数据并打印出来。

import android.content.ContentValues;import android.database.Cursor;import android.net.Uri;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;public class ContentProviderActivity extends AppCompatActivity {    private final static String TAG = "ContentProviderActivity";    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_content_provider);        Uri uri = Uri.parse("content://com.example.liuwangshu.mooncontentprovide.GameProvider");        ContentValues mContentValues = new ContentValues();        mContentValues.put("_id", 2);        mContentValues.put("name", "大航海时代ol");        mContentValues.put("describe", "最好玩的航海网游");        getContentResolver().insert(uri, mContentValues);        Cursor gameCursor = getContentResolver().query(uri, new String[]{"name", "describe"}, null, null, null);        while (gameCursor.moveToNext()) {            Game mGame = new Game(gameCursor.getString(0), gameCursor.getString(1));            Log.i(TAG, mGame.gameName + "---" + mGame.gameDescribe);        }    }}

Game.java

public class Game implements Parcelable {    public String gameName;    public String gameDescribe;    public Game(String gameName, String gameDescribe) {        this.gameName = gameName;        this.gameDescribe = gameDescribe;    }    protected Game(Parcel in) {        gameName = in.readString();        gameDescribe = in.readString();    }    public static final Creator
     
       CREATOR = new Creator
      
       () {        @Override        public Game createFromParcel(Parcel in) {            return new Game(in);        }        @Override        public Game[] newArray(int size) {            return new Game[size];        }    };    @Override    public int describeContents() {        return 0;    }    @Override    public void writeToParcel(Parcel dest, int flags) {        dest.writeString(gameName);        dest.writeString(gameDescribe);    }}
      
     

我们运行程序，发现GameProvider运行在另一个进程 

log中也打印出了我们想要的结果，打出了两条游戏信息：