Android进阶——ContentProvider&ContentResolver

学习使用ContentProvider

前言：我们为什么要学习ContentProvider与ContentResolver？

当我们想要跨进程共享多媒体数据时，就可以通过ContentProvider将多媒体数据共享出来，其它APP就可以通过ContentResolver来获取所需数据。

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（一）ContentProvider与ContentResolver的含义

ContentProvider概念：

ContentProvider是Android的四大组件之一；
ContentProvider是一种数据包装器，提供统一的接口对数据进行操作；
ContentProvider主要用于不同程序或者不同应用之间的数据共享。

ContentResolver的概念：

ContentResolver是数据调用者，ContentProvider将数据发布出来后，通过ContentResolver对象结合Uri进行调用；
通过 ContentResolver可以调用ContentProvider的增、删、改、查操作。

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（二）Uri和UriMatcher

Uri

Uri是一种资源标识符，代表要操作数据的地址，在调用ContentProvider之前，一定要确定Uri。

参考样式：

content://com.example.asus.studentdemo.provider

UriMatcher

通过UriMatcher对象的addURI方法来定义Uri规则，也就是验证口令，其一是验证authority(Uri资源存放位置)，其二验证path(Uri中的资源路径)。

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（三）创建自定义ContentProvider的步骤

1. 使用SQLite技术，创建好数据库和数据表；
2. 新建类继承ContentProvider；
3. 创建UriMatcher,定义Uri规则；
4. 重写6个抽象方法（onCreate、insert、delete、getType、update、query）；
5. 在AndroidManifest中注册Provider；
6. ContentResolver 对ContentProvider共享的数据进行增删改查。

步骤图：

这里我们一定要记得在资源提供者的AndroidManifest中注册provider

<provider
            android:enabled="true"
            android:exported="true"
            android:authorities="com.example.asus.studentdemo.provider"
            android:name=".MyProvider"/>

（四）ContentProvider的实例

内容提供方创建类继承ContentProvider：

public class MyProvider extends ContentProvider {

    private String TAG = "StudentResolver";

    private SQLiteDatabase database;


//    private  static  final int STUDENT=0;
//    private  static final  int STUDENT_ITEM=1;
//    private  static  final int TEACHER=2;
//    private  static final  int TEACHER_ITEM=3;
//    private  static final  String AUTHORITY="com.example.asus.studentdemo.provider";
//    private static UriMatcher uriMatcher;
//    static {
//        uriMatcher=new UriMatcher(UriMatcher.NO_MATCH);
//        uriMatcher.addURI(AUTHORITY,"student",STUDENT);
//        uriMatcher.addURI(AUTHORITY,"student/#",STUDENT_ITEM);
//        uriMatcher.addURI(AUTHORITY,"teacher",TEACHER);
//        uriMatcher.addURI(AUTHORITY,"teacher/#",TEACHER_ITEM);
//    }


    @Override
    public boolean onCreate() {
        Log.e(TAG, "onCreate..........");
        return false;
    }


    //查找
    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        Log.e(TAG, "query..........");
        DBHelper dbHelper = new DBHelper(getContext(), "SQLName", null, 1);
        database = dbHelper.getReadableDatabase();
        Cursor cursor = null;
        cursor = database.query("student", projection, selection, selectionArgs, null, null, sortOrder);
        return cursor;
    }

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


    //增加
    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {

//        int m=uriMatcher.match(uri);
        Log.e(TAG, "insert..........");
        DBHelper dbHelper = new DBHelper(getContext(), "SQLName", null, 1);
        SQLiteDatabase database = dbHelper.getWritableDatabase();
//        ContentValues v=new ContentValues();
//        v.put("name","xiaomeinv");
        database.insert("student", null, values);
        return null;
    }

    //删除
    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        Log.e(TAG, "delete..........");
        DBHelper dbHelper = new DBHelper(getContext(), "SQLName", null, 1);
        SQLiteDatabase database = dbHelper.getWritableDatabase();
        database.delete("student",selection,selectionArgs);
        return 100;
    }


    //修改
    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        Log.e(TAG, "update..........");
        DBHelper dbHelper = new DBHelper(getContext(), "SQLName", null, 1);
        SQLiteDatabase database = dbHelper.getWritableDatabase();
        int updateRows=0;
        updateRows=database.update("student",values,selection,selectionArgs);
        return updateRows;
    }
}

内容提供方注册provider

 <provider
            android:enabled="true"
            android:exported="true"
            android:authorities="com.example.asus.studentdemo.provider"
            android:name=".MyProvider"/>

内容接收方对分享数据进行增删改查

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    private Button ceshiBtn;
    private Button insertBtn;
    private Button deleteBtn;
    private Button updateBtn;
    private Button queryBtn;

    private EditText insertET;
    private EditText deleteET;
    private EditText updateBeforeET;
    private EditText updateAfterET;


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

        bindID();
    }

    private void bindID() {
        ceshiBtn = findViewById(R.id.ceshi_btn);
        insertBtn = findViewById(R.id.insert_btn);
        deleteBtn = findViewById(R.id.delete_btn);
        updateBtn = findViewById(R.id.update_btn);
        queryBtn = findViewById(R.id.query_btn);

        insertET = findViewById(R.id.insert_et);
        deleteET = findViewById(R.id.delete_et);
        updateBeforeET = findViewById(R.id.updatebefore__et);
        updateAfterET = findViewById(R.id.updateafter_et);

        ceshiBtn.setOnClickListener(this);
        insertBtn.setOnClickListener(this);
        deleteBtn.setOnClickListener(this);
        updateBtn.setOnClickListener(this);
        queryBtn.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            //测试按钮
            case R.id.ceshi_btn:
                Uri uri = Uri.parse("content://com.example.asus.studentdemo.provider");
                ContentResolver resolver = getContentResolver();
                resolver.delete(uri, null, null);
                break;


                //插入按钮
            case R.id.insert_btn:
                String name=insertET.getText().toString();
                Uri uri1 = Uri.parse("content://com.example.asus.studentdemo.provider");
                ContentResolver resolver1=getContentResolver();
                ContentValues values=new ContentValues();
                values.put("name",name);
                resolver1.insert(uri1,values);
                break;


                //删除按钮
            case R.id.delete_btn:
                Uri uri2=Uri.parse("content://com.example.asus.studentdemo.provider");
                ContentResolver resolver2=getContentResolver();
                resolver2.delete(uri2,"name=?",new String[]{deleteET.getText().toString()});
                break;


                //修改按钮
            case R.id.update_btn:
                String aftername=updateAfterET.getText().toString();
                Uri uri3=Uri.parse("content://com.example.asus.studentdemo.provider");
                ContentResolver resolver3=getContentResolver();
                ContentValues values3=new ContentValues();
                values3.put("name",aftername);
                resolver3.update(uri3,values3,"name=?",new String[]{updateBeforeET.getText().toString()});
                break;


                //查找按钮
            case R.id.query_btn:
                Uri uri4=Uri.parse("content://com.example.asus.studentdemo.provider/student");
                Cursor cursor=getContentResolver().query(uri4,null,null,null,null);
                if (cursor!=null){
                    while (cursor.moveToNext()){
                        String sname=cursor.getString(cursor.getColumnIndex("name"));
                        Log.e( "onClick: ",sname );
                    }
                    cursor.close();
                }
                break;
        }

    }
}