四大組件之內容提供者——ContentProvider

ContentProvider要結合數據庫進行使用，ContentProvider就是在其他的項目中獲取數據庫中的內容，並且對其進行操作（增、刪、改、查）。

對ContentProvider進行操作需要借助uriMatcher（匹配器）。

ContentProvider代碼

static{

    uriMatcher.addURI("wang.provider","query",0);
    uriMatcher.addURI("wang.provider","insert",1);
    uriMatcher.addURI("wang.provider","delete",2);
    uriMatcher.addURI("wang.provider","update",3);
}

@Override
public boolean onCreate() {
    mySql =new MySql(getContext());
    database =mySql.getWritableDatabase();
    return false;
}

@Nullable
@Override
public Cursorquery(@NonNullUri uri, @Nullable String[] projection,@Nullable String selection,@Nullable String[]selectionArgs,@Nullable String sortOrder) {
   if (uriMatcher.match(uri) ==0){
    Cursor cursor = database.query("user1",projection,selection,selectionArgs,null,null,sortOrder);
        return cursor;
   }else{
       return null;
   }
}

@Nullable
@Override
public StringgetType(@NonNullUri uri) {
    return null;
}

@Nullable
@Override
public Uri insert(@NonNullUri uri, @Nullable ContentValuesvalues) {
    if(uriMatcher.match(uri) ==1){
        Long code = database.insert("user1",null,values);
        Uri uri1 = Uri.parse("wang.provider/insert"+code);
        return uri1;
    }else{
        return null;
    }
}

@Override
public int delete(@NonNullUri uri, @Nullable String selection,@Nullable String[] selectionArgs) {
    if(uriMatcher.match(uri) ==2){
        /**
         * 返回值被影響的行數
         * */
   int code=database.delete("user1",selection,selectionArgs);
        return code;

    }else{
        return -1;
    }
}

@Override
public int update(@NonNullUri uri, @Nullable ContentValues values,@NullableString selection,@NullableString[] selectionArgs) {
    if(uriMatcher.match(uri) ==3){
        /**
         * 返回值被影響的行數
         * */
    int code=database.update("user1",values,selection,selectionArgs);
    return code;
    }else{
        return -1;
    }
}

其他程序中調用的代碼：

@RequiresApi(api = Build.VERSION_CODES.JELLY_BEAN)
public void query_(View view){
    Uri uri = Uri.parse("content://wang.provider/query");
    Cursor cursor = resolver.query(uri,null,null,null,null,null);
    if(cursor != null){
        while(cursor.moveToNext()){
            String name = cursor.getString(1);
            String age = cursor.getString(2);
            Log.e("MainActivity", name + "我是其他程序來調用你的！" + age);
        }
    }

}

public void insert_(View view){
Uri uri = Uri.parse("content://wang.provider/insert");
    ContentValues values = new ContentValues();
    values.put("name","haha");
    values.put("age",20);
    resolver.insert(uri,values);
}



public void delete_(View view){
    Uri uri = Uri.parse("content://wang.provider/delete");
    resolver.delete(uri,"name = ?",new String[]{"coco"});
}


public void update_(View view){
    Uri uri = Uri.parse("content://wang.provider/update");
    ContentValues values = new ContentValues();
    values.put("name","xixi");
    resolver.update(uri,values,"name = ?",new String[]{"haha"});

}

  ContentProvider主要用於系統間程序·的相互訪問。