ContentProvider的使用以及操作数据库

由于APP开发很少需要把自己的数据暴露出来，所以contentProvider不经常使用，下边就详细的记录一下怎么使用。

首先需要在自己的应用中重写SQLiteOpenHelper

public class DBHelper extends SQLiteOpenHelper {

    // 数据库名
    private static final String DATABASE_NAME = "finch.db";

    // 表名
    public static final String USER_TABLE_NAME = "user";

    private static final int DATABASE_VERSION = 1;
    //数据库版本号

    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE IF NOT EXISTS " + USER_TABLE_NAME + "(_id integer primary key autoincrement,name varchar(20),money varchar(20))");
        db.execSQL("insert into " + USER_TABLE_NAME + "(name,money) values(?,?)", new String[]{"李四", "3000"});
    }

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

        // 版本更新时
    }
}

然后写一个类继承ContentProvider

public class AutoProvider extends ContentProvider {

    //[1]定义一个路径的匹配器 
    private static final UriMatcher sURIMatcher = new UriMatcher(UriMatcher.NO_MATCH);
    private static final int QUERYSUCESS = 0;
    private static final int INSERTSUCESS = 1;
    private static final int UPDATESUCESS = 2;
    private static final int DELETESUCESS = 3;
    private DBHelper myOpenHelper;
    // 这个就是你在xml中写的 android:authorities="cn.scu.myprovider" 千万不要写错了！！！
    public static final String AUTOHORITY = "cn.scu.myprovider"; 
    // 表名
    public static final String USER_TABLE_NAME = "user";

    //[2]添加一个静态代码块 在这个代码块里面添加匹配的规则 
    static{
        sURIMatcher.addURI(AUTOHORITY,"query", QUERYSUCESS);
        sURIMatcher.addURI(AUTOHORITY, "insert", INSERTSUCESS);
        sURIMatcher.addURI(AUTOHORITY, "update", UPDATESUCESS);
        sURIMatcher.addURI(AUTOHORITY, "delete", DELETESUCESS);


    }


    @Override
    public boolean onCreate() {
        myOpenHelper = new DBHelper(getContext());

        return false;
    }

    //这个方法是被其他应用调用的
    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
        //通过这个方法对数据库进行查询的操作 
        int code = sURIMatcher.match(uri);
        if (code == QUERYSUCESS ) {
            //说明路径匹配成功 
            SQLiteDatabase db = myOpenHelper.getReadableDatabase();
            //对数据库进行查询操作 
            Cursor cursor = db.query(USER_TABLE_NAME, projection, selection, selectionArgs, null, null, sortOrder);

            //自己主动的发一条消息  告诉系统 数据库被操作 
            getContext().getContentResolver().notifyChange(uri, null);

            return cursor;

        }else {
            //说明路径匹配失败
            throw new IllegalArgumentException("哥们 路径不正确,请检查路径");

        }


    }

    @Override
    public String getType(Uri uri) {
        return null;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        int code = sURIMatcher.match(uri);
        if (code == INSERTSUCESS) {
            //说明路径匹配成功 
            SQLiteDatabase db = myOpenHelper.getReadableDatabase();
            //对数据库进行增加一条记录 
            long insert = db.insert(USER_TABLE_NAME, null, values);
            if (insert>0) {
                //当数据库被人操作了  自己主动发一条消息
                getContext().getContentResolver().notifyChange(uri, null);
            }

            Uri uri2 = Uri.parse("com.itheima.haha.insert/"+insert);
            return uri2;

        }else {
            //说明路径匹配失败
            throw new IllegalArgumentException("哥们 路径不正确,请检查路径");
        }


    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        int code = sURIMatcher.match(uri);
        if (code == DELETESUCESS) {
            //说明路径匹配成功 
            SQLiteDatabase db = myOpenHelper.getReadableDatabase();
            int delete = db.delete(USER_TABLE_NAME, selection, selectionArgs);
            if(delete>0){
                //当数据库被人操作了  自己主动发一条消息
                getContext().getContentResolver().notifyChange(uri, null);
            }
            return delete;

        }else {
            //说明路径匹配失败
            throw new IllegalArgumentException("爷们 路径不正确,请检查路径");
        }
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
                      String[] selectionArgs) {

        int code = sURIMatcher.match(uri);
        if (code == UPDATESUCESS) {
            //说明路径匹配成功 
            SQLiteDatabase db = myOpenHelper.getReadableDatabase();
            int update = db.update(USER_TABLE_NAME, values, selection, selectionArgs);

            if (update>0) {
                //当数据库被人操作了  自己主动发一条消息
                getContext().getContentResolver().notifyChange(uri, null);

            }
            return update;

        }else {
            //说明路径匹配失败
            throw new IllegalArgumentException("爷们 路径不正确,请检查路径");
        }
    }

}

为了让其他应用可以访问，你还需要在xml中这样写

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />



 <provider
            android:name=".contentProvider.AutoProvider"
            android:authorities="cn.scu.myprovider"
            android:exported="true"
            />

在本地你可以这样操作数据库

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private Button btn;
    private Button btn1;
    private Button btn2;
    private Button btn3;
    private DBHelper dbHelper;

    public static final String USER_TABLE_NAME = "user";
    private SQLiteDatabase writableDatabase;
    private SQLiteDatabase readableDatabase;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        btn = findViewById(R.id.btn);
        btn1 = findViewById(R.id.btn1);
        btn2 = findViewById(R.id.btn3);
        btn3 = findViewById(R.id.btn3);

        btn.setOnClickListener(this);
        btn1.setOnClickListener(this);
        btn2.setOnClickListener(this);
        btn3.setOnClickListener(this);

        dbHelper = new DBHelper(getApplicationContext());
        writableDatabase = dbHelper.getWritableDatabase();
        readableDatabase = dbHelper.getReadableDatabase();

    }

    @Override
    public void onClick(View v) {

        switch (v.getId()) {
            case R.id.btn://增加数据
                ContentValues values = new ContentValues();
                values.put("name", "zhangsan");
                values.put("money", "234");
                readableDatabase.insert(USER_TABLE_NAME, null, values);
                break;

            case R.id.btn1:// 更新数据
                ContentValues values1 = new ContentValues();
                values1.put("money", "1234");
                readableDatabase.update(USER_TABLE_NAME, values1, "name=?", new String[]{"zhangsan"});
                break;

            case R.id.btn2://查询数据
//              Cursor cursor=  readableDatabase.query(USER_TABLE_NAME,null,null,null,null,null,null);
                break;

            case R.id.btn3: //删除数据
                readableDatabase.delete(USER_TABLE_NAME,"name=?", new String[]{"李四"});
                break;

        }

        Cursor cursor = readableDatabase.query(USER_TABLE_NAME, null, null, null, null, null, null);
        if (cursor != null && cursor.getCount() > 0) {
            while (cursor.moveToNext()) {
                //把name和money取出来
                String name = cursor.getString(1);
                String money = cursor.getString(2);
                System.out.println("=====name:" + name + "----" + money);

            }
            cursor.close();
        }
    }
}

下边就是本部分的重点了，第三方应用如何访问呢？

在三方的应用中

public class MainActivity extends AppCompatActivity {

    private String uri_user = "content://cn.scu.myprovider/";


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    }

    //点击按钮向数据库增加一条记录
    public void click1(View v) {
        // [1]由于第一个应用的数据库内容已经通过内容提供者暴露出来 所以我可以直接通过内容解析者去访问
        Uri uri = Uri.parse(uri_user + "/insert");
        ContentValues values = new ContentValues();
        values.put("name", "王五"); //key就是字段的名字  value就是值
        values.put("money", "1000");
        Uri insertUri = getContentResolver().insert(uri, values);
        System.out.println(insertUri);


    }

    //点击按钮删除
    public void click2(View v) {
        Uri uri = Uri.parse(uri_user + "/delete");
        int delete = getContentResolver().delete(uri, "name=?", new String[]{"王五"});
        Toast.makeText(getApplicationContext(), "删除了" + delete + "行", 1).show();

    }

    //点击按钮更新
    public void click3(View v) {
        Uri uri = Uri.parse(uri_user + "/update");
        ContentValues values = new ContentValues();
        values.put("money", "10000");//更新钱
        int update = getContentResolver().update(uri, values, "name=?", new String[]{"王五"});
        Toast.makeText(getApplicationContext(), "更新了" + update + "行", 1).show();

    }

    //点击按钮查询数据库
    public void click4(View v) {
        // [1]由于第一个应用的数据库内容已经通过内容提供者暴露出来 所以我可以直接通过内容解析者去访问
        Uri uri = Uri.parse(uri_user + "/query");
        Cursor cursor = getContentResolver().query(uri, null, null, null, null);
        while (cursor.moveToNext()) {
            // 把name和money取出来
            String name = cursor.getString(1);
            String money = cursor.getString(2);
            System.out.println("第二个应用name:" + name + "----" + money);

        }

    }

最后，不要忘了在清单文件中添加权限

  <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />