Android ContentProvider内容提供者详解

Posted 2022-11-17

前言：为什么要有ContentProvider？

ContentProvider 内容提供者：可以实现在不同程序之间数据共享的功能，同时还能够保证被访问的数据的安全性。

ContentProvider的理解

相关的API如下所示

两个重要知识点：

1.数据模型： ConentProvider使用基于数据模型的简单表格来提供其中的数据。 每一行代表一条记录，每一列代表特定类型，和含义的数据

2. Uri :统一资源标识符，比较笼统的定位了资源，不局限于客户端和服务器

结构如下：

下面创建一个应用A，提供数据并创建ContentProvider，供应用B进行增删改查的操作

应用A

1、创建PersonContentProvider类

/**
 * 操作person表的provider类
 */
public class PersonContentProvider extends ContentProvider 
    //用来存放所有合法的Uri容器
    private static UriMatcher uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);

    //保存一些合法的Uri
    //content://com.example.customviewproject.personcontentprovider/person  不根据id操作
    //content://com.example.customviewproject.personcontentprovider/person/3 根据id操作
    static 
        uriMatcher.addURI("com.example.customviewproject.personcontentprovider", "/person", 1);
        uriMatcher.addURI("com.example.customviewproject.personcontentprovider", "/person/#", 2);//#匹配任意数字
    

    private DBHelper dbHelper;

    public PersonContentProvider() 
        Log.i("TAG", "PersonContentProvider() ");
    

    @Override
    public boolean onCreate() 
        Log.i("TAG", "onCreate() ");
        dbHelper = new DBHelper(getContext());
        return false;
    

    /**
     * //content://com.example.customviewproject.personcontentprovider/person  不根据id查询
     * //content://com.example.customviewproject.personcontentprovider/person/3 根据id查询
     */
    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) 
        Log.i("TAG", "query() ");
        //得到连接对象
        SQLiteDatabase database = dbHelper.getReadableDatabase();
        //1.匹配uri,返回code
        int code = uriMatcher.match(uri);
        //2.如果合法,进行查询
        if (code == 1) //不根据id查询
            Cursor cursor = database.query("person", projection, selection, selectionArgs, null, null, null);
            return cursor;
         else if (code == 2) //根据id查询
            //得到id
            long id = ContentUris.parseId(uri);
            //查询
            Cursor cursor = database.query("person", projection, "_id=?", new String[]id + "", null, null, null);
            return cursor;
         else //3.如果不合法，抛出异常
            throw new RuntimeException("查询的URI不合法");
        
    


    /**
     * //content://com.example.customviewproject.personcontentprovider/person  插入
     * //content://com.example.customviewproject.personcontentprovider/person/3 根据id插入（没有）
     */
    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) 
        Log.i("TAG", "insert() ");
        //得到连接对象
        SQLiteDatabase database = dbHelper.getReadableDatabase();
        //1.匹配uri,返回code
        int code = uriMatcher.match(uri);
        //2.如果合法,进行插入
        if (code == 1) 
            long id = database.insert("person", null, values);
            //将id添加到uri中
            database.close();
            return ContentUris.withAppendedId(uri, id);
         else 
            database.close();
            throw new RuntimeException("插入的URI不合法");
        
    

    /**
     * //content://com.example.customviewproject.personcontentprovider/person  不根据id删除
     * //content://com.example.customviewproject.personcontentprovider/person/3 根据id删除
     */
    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) 
        Log.i("TAG", "delete() ");
        //得到连接对象
        SQLiteDatabase database = dbHelper.getReadableDatabase();
        //1.匹配uri,返回code
        int code = uriMatcher.match(uri);
        int deleteCount = -1;
        //2.如果合法,进行删除
        if (code == 1) 
            deleteCount = database.delete("person", selection, selectionArgs);
         else if (code == 2) 
            long id = ContentUris.parseId(uri);
            deleteCount = database.delete("person", "_id=" + id, null);
         else 
            throw new RuntimeException("删除的URI不合法");
        
        return deleteCount;
    

    /**
     * //content://com.example.customviewproject.personcontentprovider/person  不根据id更新
     * //content://com.example.customviewproject.personcontentprovider/person/3 根据id更新
     */
    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) 
        Log.i("TAG", "update() ");
        //得到连接对象
        SQLiteDatabase database = dbHelper.getReadableDatabase();
        //1.匹配uri,返回code
        int code = uriMatcher.match(uri);
        int deleteCount = -1;
        //2.如果合法,进行更新
        if (code == 1) //不根据id更新
            deleteCount = database.update("person", values, selection, selectionArgs);
         else if (code == 2) 
            long id = ContentUris.parseId(uri);
            deleteCount = database.update("person", values, "_id=" + id, null);
        
        return deleteCount;
    

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) 
        Log.i("TAG", "getType() ");
        return null;
    

2、在androidManifest.xml中注册provider

<!--authorities 自定义：一般是内容提供者类的全类名，全部小写-->
    <!--enabled:表示是否启动内容提供者-->
    <!--exported：表示是否允许该内容提供者接收本程序以外的对数据的操作 默认不允许false-->
        <provider
            android:name=".content.PersonContentProvider"
            android:authorities="com.example.customviewproject.personcontentprovider"
            android:enabled="true"
            android:exported="true" />

当应用A启动后，就会创建PersonContentProvider类对象

打印的日志如下

I/TAG: PersonContentProvider() 
I/TAG: onCreate()

应用B 通过ContentResolver对应用A中的数据进行增删改查操作

public class MainActivity extends AppCompatActivity 
    private Button btn_query;
    private Button btn_insert;
    private Button btn_delete;
    private Button btn_update;

    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn_query = findViewById(R.id.btn_query);
        btn_insert = findViewById(R.id.btn_insert);
        btn_delete = findViewById(R.id.btn_delete);
        btn_update = findViewById(R.id.btn_update);
        btn_query.setOnClickListener(onClickListener);
        btn_insert.setOnClickListener(onClickListener);
        btn_delete.setOnClickListener(onClickListener);
        btn_update.setOnClickListener(onClickListener);
    

    private final View.OnClickListener onClickListener = new View.OnClickListener() 
        @Override
        public void onClick(View view) 
            switch (view.getId()) 
                case R.id.btn_query:
                    query();
                    break;
                case R.id.btn_insert:
                    insert();
                    break;
                case R.id.btn_update:
                    update();
                    break;
                case R.id.btn_delete:
                    delete();
                    break;
                default:
                    break;
            
        
    ;

    /**
     * 通过ContentResolver调用ContentProvider删除一条记录
     */
    private void delete() 
        //1.得到ContentResolver对象
        ContentResolver resolver = getContentResolver();
        //2.调用其insert
        Uri uri = Uri.parse("content://com.example.customviewproject.personcontentprovider/person/2");
        int deleteCount = resolver.delete(uri, null, null);
        Toast.makeText(this, "deleteCount=" + deleteCount, Toast.LENGTH_SHORT).show();
    

    /**
     * 通过ContentResolver调用ContentProvider更新一条记录
     */
    private void update() 
        //1.得到ContentResolver对象
        ContentResolver resolver = getContentResolver();
        //2.调用其insert
        Uri uri = Uri.parse("content://com.example.customviewproject.personcontentprovider/person/3");
        ContentValues contentValues = new ContentValues();
        contentValues.put("name", "Jack2");
        int updateCount = resolver.update(uri, contentValues, null, null);
        Toast.makeText(this, "updateCount=" + updateCount, Toast.LENGTH_SHORT).show();
    


    /**
     * 通过ContentResolver调用ContentProvider插入一条记录
     */
    private void insert() 
        //1.得到ContentResolver对象
        ContentResolver resolver = getContentResolver();
        //2.调用其insert
        Uri uri = Uri.parse("content://com.example.customviewproject.personcontentprovider/person");
        ContentValues contentValues = new ContentValues();
        contentValues.put("name", "Jack");
        uri = resolver.insert(uri, contentValues);
        Toast.makeText(this, uri.toString(), Toast.LENGTH_SHORT).show();
    

    /**
     * 通过ContentResolver调用ContentProvider查询所有记录
     */
    private void query() 
        //1.得到ContentResolver对象
        ContentResolver resolver = getContentResolver();
        //2.调用其query,得到cursor
//        Uri uri = Uri.parse("content://com.example.customviewproject.personcontentprovider/person/1");
        //查询所有
        Uri uri = Uri.parse("content://com.example.customviewproject.personcontentprovider/person");
        Cursor cursor = resolver.query(uri, null, null, null, null);
        //3.取出cursor中的数据，并显示
        while (cursor.moveToNext()) 
            int id = cursor.getInt(0);
            String name = cursor.getString(1);
//            Toast.makeText(this, id + ":" + name, Toast.LENGTH_SHORT).show();
            Log.i("TAG", id + ":" + name);
        
        cursor.close();
    

效果就不展示了，能对应用A中的数据库表进行CRUD操作。

接下来我们通过Content Provider 读取通讯录中所有的联系人姓名：
布局代码就不贴出来了。
主要是Activity代码：
详细注解已经在代码中给出

public class ContentProviderActivity extends AppCompatActivity 
    private TextView tv_phone;
    private String name = ContactsContract.Contacts.DISPLAY_NAME;//获得通讯录中的姓名
    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_content_provider);
        tv_phone = findViewById(R.id.tv_phone);

        //显示获取的通讯录信息
        tv_phone.setText(getQueryData());
    
    private CharSequence getQueryData()
        //用于保存获取的联系人姓名
        StringBuilder stringBuilder = new StringBuilder();
        ContentResolver resolver = getContentResolver();
        //通过通讯录进行查询
        Cursor cursor = resolver.query(ContactsContract.Contacts.CONTENT_URI,null,null,null,null);
        //获得姓名记录的索引值
        int displayNameIndex = cursor.getColumnIndex(name);
        for (cursor.moveToFirst(); !cursor.isAfterLast() ; cursor.moveToNext()) 
            String display = cursor.getString(displayNameIndex);
            stringBuilder.append(display+"\\n");
        
        cursor.close();
        //返回查询的结果
        return stringBuilder.toString();
    

从通讯录中便获取到了联系人姓名：