ContentProvider是Android实现跨程序共享数据的标准方式。
主要用于，一个程序访问另一个程序中允许共享的数据，同时还能保证被访问数据的安全性。

ContentProvider基本用法

1.  ContentResolver
如果想访问ContentProvider中共享的数据，就需要借助ContentResolver类。
通过Context提供的getContentResolver()获取，ContentResolver提供了一系列的CRUD操作。

内容Uri
ContentResolver的CRUD不接收表名参数，而是用一个Uri代替。
组成：
    authority：用于区分不同的应用程序，一般用程序包名命名。
    path：用于对同一程序不同表做区分，通常添加到authority后。

程序A定义ContentProvider，共享数据。

1.  定义数据库
public class UserDb extends SQLiteOpenHelper {

    public UserDb(Context context) {
        super(context, "user.db", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        sqLiteDatabase.execSQL("create table if not exists " +
                "t_user(_id integer primary key autoincrement," +
                "name text," +
                "code integer)");

        sqLiteDatabase.execSQL("insert into t_user(name,code)" +
                "values('Demo1',1),('Demo2',2) ");
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    }
}


2.  定义Provider共享数据
public class MyProviderDemo extends ContentProvider {

    private static final String TAG = "MyProviderDemo";
    private static final UriMatcher URI_MATCHER = new UriMatcher(UriMatcher.NO_MATCH);
    
    private static int URI_MATCHER_SUCCESS = 0;

    private UserDb mUserDb;

    static {
        /**
         * 参数注意
         * authority 要和配置清单中一致
         * path 内容解析者调用的路径  com.w.review/query
         * code 匹配成功的返回码
         */
        URI_MATCHER.addURI("com.w.review", "query", URI_MATCHER_SUCCESS);
    }

    @Override
    public boolean onCreate() {
        mUserDb = new UserDb(getContext());
        return false;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri,
                        @Nullable String[] projection,
                        @Nullable String selection,
                        @Nullable String[] selectionArgs,
                        @Nullable String sortOrder) {

        int code = URI_MATCHER.match(uri); //别的程序调用，匹配时查询成功时返回

        if (code == URI_MATCHER_SUCCESS) {

            SQLiteDatabase database = mUserDb.getReadableDatabase();
            Cursor cursor = database.query("t_user", projection,
                    selection, selectionArgs, 
                    null, null, sortOrder);

            return cursor;
        } else {
            Log.i(TAG, "参数异常" + code);
            throw new IllegalArgumentException("参数异常");
        }
    }

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

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, 
                      @Nullable ContentValues values) {
        return null;
    }

    @Override
    public int delete(@NonNull Uri uri, 
                      @Nullable String selection,
                      @Nullable String[] selectionArgs) {

        return 0;
    }

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

        return 0;
    }
}


3.  mainfests内声明
<application>
    <provider
        android:name=".provider.MyProviderDemo"
        android:authorities="com.w.review"
        android:enabled="true"
        android:exported="true">
    </provider>
</application>

程序B查询A的共享数据
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);

        getProviderData();
    }

    private void getProviderData() {
        //注意：规定一定要跟头路径content://
        Uri uri = Uri.parse("content://com.w.review/query");

        Cursor cursor = getContentResolver().query(uri, new String[]{"name"},
                null, null, null);

        if (cursor != null && cursor.getCount() > 0) {
            while (cursor.moveToNext()) {
                String value = cursor.getString(0);
                Log.i(TAG, value);
            }
            cursor.close();

        } else {
            Log.i(TAG, "fail");
        }
    }
}

获取手机联系人

权限
<uses-permission android:name="android.permission.READ_CONTACTS"/>

public class MainActivity extends AppCompatActivity {

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

        getPermission();
    }

    //6.0后需要动态申请权限
    private void getPermission() {
        int checkPermission = ContextCompat.checkSelfPermission(this, Manifest.permission.READ_CONTACTS);
        if (checkPermission != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(MainActivity.this,
                    new String[]{Manifest.permission.READ_CONTACTS}, 0);
        } else {
            getLinkMan();
        }
    }

    private void getLinkMan() {
        Cursor cursor = getContentResolver().query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,
                null, null, null, null);
        if (cursor != null) {
            while (cursor.moveToNext()) {
                String name = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
                String number = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));
                Log.i("TAG", name + "\r\n" + number);
            }
            cursor.close();
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        switch (requestCode) {
            case 0:
                if (grantResults.length > 0 && grantResults[0] == PackageManager.GET_RECEIVERS) {
                    getLinkMan();
                } else {
                    Toast.makeText(MainActivity.this, "没有读取权限", Toast.LENGTH_SHORT).show();
                }
                break;
            default:
                break;
        }
    }
}