Android 藝術開發(fā)探索筆記--進程間通信ContentProvider

1ContentProvider是Android中提供的專門用于不同應用間進行數(shù)據(jù)共享的方式，從這一點看，它天生適合進程間通信。和Messenger一樣，ContentProvider的底層實現(xiàn)也是Binder。系統(tǒng)預置了許多ContentProvider,比如通訊錄信息，日程表信息等，要跨進程的訪問這些信息，只需要通過ContentReslover的query,update,insert,和delete方法.

2 使用方法
首先，我們創(chuàng)建一個ContentProvider,實現(xiàn)六個抽象方法即可：onCreate,query,update,insert,delete和getType.onCreate代表ContentProvider的創(chuàng)建，一般用來做一些初始化的操作；getType用來返回一個Uri請求對應的MIME類型（媒體類型），比如圖片，視頻等。根據(jù)Binder的工作原理，我們知道這六個方法均運行在ContentProvider的進程中，除了onCreate()有系統(tǒng)回調(diào)并運行在主線程里，其他五個方法均有外界回調(diào)并運行在Binder線程池中。

3直接看代碼

package com.zhouzhuo.conentprovidermaster;

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;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.util.Log;

/**
 * Created by zhouzhuo on 2018/1/3.
 */

public class BookProvider extends ContentProvider {
    private static final String TAG = "BookProvider";
    private static final String AUTHORITY = "com.zhouzhuo.conentprovidermaster.BookProvider";

    private static final Uri BOOK_CONTENT_URI = Uri.parse("content://"
                        +AUTHORITY+"/book");
    private static final Uri USER_CONTENT_URI = Uri.parse("content://"
                        +AUTHORITY+"/user");
    public static final int BOOK_URI_CODE = 0;

    public static final int USER_URI_CODE = 1;

    private static final UriMatcher sUriMather = new UriMatcher(UriMatcher.NO_MATCH);

    static {
        sUriMather.addURI(AUTHORITY,"book",BOOK_URI_CODE);
        sUriMather.addURI(AUTHORITY,"user",USER_URI_CODE);
    }

    private Context mContext;
    private SQLiteDatabase mDb;

    @Override
    public boolean onCreate() {
        Log.d("zhouzhuo","onCreate,current thread:"+Thread.currentThread().getName());
        mContext = getContext();
        initProviderData();
        return true;
    }

    private void initProviderData() {
        mDb = new DbOpenHelper(mContext).getWritableDatabase();
        mDb.execSQL("delete from " + DbOpenHelper.BOOK_TABLE_NAME);
        mDb.execSQL("delete from " + DbOpenHelper.USER_TABLE_NAME);
        mDb.execSQL("insert into book values(3,'Android');");
        mDb.execSQL("insert into book values(4,'Ios');");
        mDb.execSQL("insert into book values(5,'Html5');");
        mDb.execSQL("insert into user values(1,'jake',1);");
        mDb.execSQL("insert into user values(2,'jasmine',0);");
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection,
                        @Nullable String selection,
                        @Nullable String[] selectionArgs,
                        @Nullable String sortOrder) {
        Log.d("zhouzhuo","query,current thread:"+Thread.currentThread().getName());
        String table = getTableName(uri);
        if(table == null){
            throw new IllegalArgumentException("Unsupported URI:"+uri);
        }
        return mDb.query(table,projection,selection,selectionArgs,null,null,sortOrder,null);
    }

    private String getTableName(Uri uri) {
        String tableName = null;
        switch (sUriMather.match(uri)){
            case BOOK_URI_CODE:
                tableName = DbOpenHelper.BOOK_TABLE_NAME;
                break;
            case USER_URI_CODE:
                tableName = DbOpenHelper.USER_TABLE_NAME;
                break;
            default:
                break;
        }
        return tableName;

    }

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        Log.d("zhouzhuo","getType");
        return null;
    }

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        Log.d("zhouzhuo","insert");
        String table = getTableName(uri);
        if(table == null){
            throw new IllegalArgumentException("Unsupported URI:"+uri);
        }
        mDb.insert(table,null,values);
        mContext.getContentResolver().notifyChange(uri,null);
        return uri;
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        Log.d("zhouzhuo","delete");
        String table = getTableName(uri);
        if(table == null){
            throw new IllegalArgumentException("Unsupported URI:"+uri);
        }
        int count = mDb.delete(table,selection,selectionArgs);
        if(count>0){
            getContext().getContentResolver().notifyChange(uri,null);
        }
        return count;
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        Log.d("zhouzhuo","update");
        String table = getTableName(uri);
        if(table == null){
            throw new IllegalArgumentException("Unsupported URI:"+uri);
        }

        int row = mDb.update(table,values,selection,selectionArgs);
        if(row>0){
            getContext().getContentResolver().notifyChange(uri,null);
        }
        return row;
    }
}


package com.zhouzhuo.conentprovidermaster;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

/**
 * Created by zhouzhuo on 2018/1/4.
 * 數(shù)據(jù)庫管理,創(chuàng)建表
 */

public class DbOpenHelper extends SQLiteOpenHelper{
    private static final String DB_NAME = "book_provider.db";
    public static final String BOOK_TABLE_NAME = "book";
    public static final String USER_TABLE_NAME = "user";
    private static final int DB_VERSION = 3;

    private String CREATE_BOOK_TABLE = "CREATE TABLE IF NOT EXISTS "
            + BOOK_TABLE_NAME + "(_id INTEGER PRIMARY KEY," + "name TEXT)";

    private String CREATE_USER_TABLE = "CREATE TABLE IF NOT EXISTS "
            + USER_TABLE_NAME + "(_id INTEGER PRIMARY KEY," + "name TEXT,"
            + "sex INT)";
    public DbOpenHelper(Context context){
        super(context,DB_NAME,null,DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_BOOK_TABLE);
        db.execSQL(CREATE_USER_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}


package com.zhouzhuo.conentprovidermaster;

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 MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initData();
    }

    private void initData() {
        Uri bookUri = Uri.parse("content://com.zhouzhuo.conentprovidermaster.BookProvider/book");
        ContentValues values = new ContentValues();
        values.put("_id",6);
        values.put("name","程序設計的藝術");
        getContentResolver().insert(bookUri,values);
        Cursor bookCursor = getContentResolver().query(bookUri,new String[]{"_id","name"},null,null,null);
        while (bookCursor.moveToNext()){
            Book book = new Book();
            book.bookId = bookCursor.getInt(0);
            book.bookName = bookCursor.getString(1);
            Log.d("zhouzhuo","query book:"+book.toString());
        }
        bookCursor.close();
        Uri userUri = Uri.parse("content://com.zhouzhuo.conentprovidermaster.BookProvider/user");
        Cursor userCursor = getContentResolver().query(userUri,new String[]{"_id","name","sex"},null,null,null);
        while (userCursor.moveToNext()){
            User user = new User();
            user.userId = userCursor.getInt(0);
            user.userName = userCursor.getString(1);
            user.isMale = userCursor.getInt(2) ==1;
            Log.d("zhouzhuo","query user:"+user.toString());
        }
        userCursor.close();
    }
}
4 需要主要的是，query,update,insert,delete四大方法是存在多線程并發(fā)訪問的，因此方法內(nèi)部需要做好線程同步。代碼中采用的是SQLite并且只要一個SQLiteDatabase 的連接，所有可以正確應對多線程的情況。具體原因是SQLiteDatabase內(nèi)部對數(shù)據(jù)庫的操作是有同步處理的，但是如果多個SQLiteDatabase對象來操作數(shù)據(jù)庫就無法保證線程同步，因為SQLiteDatabase對象之間無法進行線程同步。
5 代碼地址
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