Android ContentProvider的使用实例

程序员文章站 2022-03-25 16:56:51

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Uri基础

Uri的四个组成部分：content：//contacts/people/5

1）schema：已由Android固定设置为content://
2）authority：ContentProvider权限，在AndroidMenifest中设置权限
3）path：要操作的数据库表
4）Id：查询的关键字（可选字段）

Uri的匹配表示要查询的数据，对于单个数据查询，可直接使用Uri定位具体的资源位置，但当范围查询时就需要结合通配符的使用，Uri提供以下两种通配符：

1）*：匹配由任意长度的任何有效字符组成的字符串
2）#：匹配由任意长度的数字字符组成的字符串

ContentProvider使用

ContentProvider一般配合数据库共同使用，实现对外共享数据的目的，所以它需要对数据库的增删改查操作

UriMatcher的作用是在使用Uri操作数据库时，根据发起请求的Uri和配置好的uriMatcher确定本次操作的数据表

ContentObserver，内容观察者，采用观察者模式在存储的数据发生修改时自动触发回调

ContentProvider的使用是通过ContentResolver实例进行操作的，调用getContentResolver()获取ContentResolver实例，进而进行增改删查

权限

android:readPermission：提供程序范围读取权限
android:writePermission：提供程序范围写入权限

数据库provider

public class StudentsProvider extends ContentProvider {
    static final String DATABASE_NAME = "College";
    static final String STUDENTS_TABLE_NAME = "students";
    static final int DATABASE_VERSION = 1;

    // 数据库表中的字段
    static final String _ID = "_id";  // 是从1开始计数
    static final String NAME = "name";
    static final String GRADE = "grade";

    private static class DatabaseHelper extends SQLiteOpenHelper {
        public DatabaseHelper(@Nullable Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(" CREATE TABLE " + STUDENTS_TABLE_NAME +
                    " (_id INTEGER PRIMARY KEY AUTOINCREMENT, " +
                    " name TEXT NOT NULL, " +
                    " grade TEXT NOT NULL)");
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            db.execSQL("DROP TABLE IF EXISTS " +  STUDENTS_TABLE_NAME);
            onCreate(db);
        }
    }

    private SQLiteDatabase db;

    static final String PROVIDER_NAME = "com.example.provider.College";
    static final Uri CONTENT_URI = Uri.parse("content://" + PROVIDER_NAME + "/students");

    static final int STUDENTS = 1;
    static final int STUDENT_ID = 2;

    static final UriMatcher uriMatcher;
    static{
        uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        uriMatcher.addURI(PROVIDER_NAME, "students", STUDENTS);
        uriMatcher.addURI(PROVIDER_NAME, "students/#", STUDENT_ID);
    }

    private static HashMap<String, String> STUDENTS_PROJECTION_MAP;

    @Override
    public boolean onCreate() {
        Context context = getContext();
        DatabaseHelper dbHelper = new DatabaseHelper(context);
        db = dbHelper.getWritableDatabase();
        return (db == null)? false:true;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
        qb.setTables(STUDENTS_TABLE_NAME);

        switch (uriMatcher.match(uri)) {
            case STUDENTS:
                qb.setProjectionMap(STUDENTS_PROJECTION_MAP);
                break;
            case STUDENT_ID:
                qb.appendWhere( _ID + "=" + uri.getPathSegments().get(1));
                break;
        }
        if (sortOrder == null || sortOrder == ""){
            sortOrder = NAME;
        }
        Cursor c = qb.query(db, projection, selection, selectionArgs,null, null, sortOrder);
        c.setNotificationUri(getContext().getContentResolver(), uri);
        return c;
    }

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

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        long rowID = db.insert(STUDENTS_TABLE_NAME, "", values);  //返回添加后的id
        if (rowID > 0) {
            Uri _uri = ContentUris.withAppendedId(CONTENT_URI, rowID);
            getContext().getContentResolver().notifyChange(_uri, null);
            return _uri;
        }
        return null;
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        int count = 0;
        switch (uriMatcher.match(uri)){
            case STUDENTS:
                count = db.delete(STUDENTS_TABLE_NAME, selection, selectionArgs);
                break;
            case STUDENT_ID:
                String id = uri.getPathSegments().get(1);
                count = db.delete( STUDENTS_TABLE_NAME, _ID +  " = " + id +
                        (!TextUtils.isEmpty(selection) ? " AND (" + selection + ')' : ""), selectionArgs);
                break;
            default:
                break;
        }
        getContext().getContentResolver().notifyChange(uri, null);
        return count;
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        int count = 0;
        switch (uriMatcher.match(uri)){
            case STUDENTS:
                count = db.update(STUDENTS_TABLE_NAME, values, selection, selectionArgs);
                break;
            case STUDENT_ID:
                count = db.update(STUDENTS_TABLE_NAME, values, _ID + " = " + uri.getPathSegments().get(1) +
                        (!TextUtils.isEmpty(selection) ? " AND (" +selection + ')' : ""), selectionArgs);
                break;
            default:
                break;
        }
        getContext().getContentResolver().notifyChange(uri, null);
        return count;
    }
}

权限设置

<provider android:name="StudentsProvider"
	android:authorities="com.example.provider.College" >
</provider>

activity操作数据库

public class MainActivity extends AppCompatActivity {
    // provider uri地址是包括表名
    private Uri studentUri = Uri.parse("content://com.example.provider.College/students");

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // 注册内容观察者ContentObserver
        getContentResolver().registerContentObserver(studentUri, true, new MyObserver(new Handler()));
    }

    public void onClickAdd(View view) {
        ContentValues values = new ContentValues();
        values.put(StudentsProvider.NAME, ((EditText)findViewById(R.id.tvName)).getText().toString());
        values.put(StudentsProvider.GRADE, ((EditText)findViewById(R.id.tvGrade)).getText().toString());
        Uri uri = getContentResolver().insert(studentUri, values);
        Toast.makeText(getBaseContext(), "onClickAdd", Toast.LENGTH_LONG).show();
    }

    // projection 是要查询的字段，是一个String[]类型，如果为null，则查询所有字段
    // selection 是where子句
    // selectionArgs 是where子句的参数

    public void onClickQuery(View view) {
        Cursor cursor = getContentResolver().query(studentUri, null, null, null, null);
        while (cursor.moveToNext()){
            int stuId = cursor.getInt(0);
            String vName = cursor.getString(cursor.getColumnIndex("name"));
            String vGrade = cursor.getString(cursor.getColumnIndex("grade"));
        }
        cursor.close();
        Toast.makeText(getBaseContext(), "onClickQuery", Toast.LENGTH_LONG).show();
    }

    public void onClickDelete(View view) {
        getContentResolver().delete(studentUri, "name=?", new String[]{"xyz"});
        Toast.makeText(getBaseContext(), "onClickDelete", Toast.LENGTH_LONG).show();
    }

    public void onClickUpdate(View view) {
        Uri uri = ContentUris.withAppendedId(studentUri, 1);
        Log.d("yy", "onClickUpdate, uri = " + uri);
        ContentValues values = new ContentValues();
        values.put(StudentsProvider.NAME, "xyz");
        getContentResolver().update(uri, values, null, null);
        Toast.makeText(getBaseContext(), "onClickUpdate", Toast.LENGTH_LONG).show();

    }

    // 监听数据库的类
    private final class MyObserver extends ContentObserver {
        public MyObserver(Handler handler) {
            super(handler);
        }

        @Override
        public void onChange(boolean selfChange, Uri uri) {
            Log.d("yy", "onChange, uri = " + uri);
            Cursor cursor = getContentResolver().query(studentUri, null, null, null, null);
            while (cursor.moveToNext()){
                int stuId = cursor.getInt(0);
                String vName = cursor.getString(cursor.getColumnIndex("name"));
                String vGrade = cursor.getString(cursor.getColumnIndex("grade"));
                Log.d("yy", "onChange, id = " + stuId + ", name = " + vName + ", grade = " + vGrade);
            }
            cursor.close();
        }
    }
}

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