android contprovider 案例

Android的ContentProvider是一种数据共享机制，可以让应用程序之间共享数据。下面是一个简单的ContentProvider案例，演示如何创建和使用ContentProvider。

1. 创建ContentProvider类

public class MyContentProvider extends ContentProvider {

    private MyDatabaseHelper dbHelper;
    private static final UriMatcher uriMatcher;

    private static final int PERSONS = 1;
    private static final int PERSON_ID = 2;

    static {
        uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        uriMatcher.addURI("com.example.myapp.provider", "persons", PERSONS);
        uriMatcher.addURI("com.example.myapp.provider", "persons/#", PERSON_ID);
    }

    @Override
    public boolean onCreate() {
        dbHelper = new MyDatabaseHelper(getContext(), "myapp.db", null, 1);
        return true;
    }

    @Nullable
    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
        SQLiteDatabase db = dbHelper.getReadableDatabase();
        Cursor cursor = null;
        switch (uriMatcher.match(uri)) {
            case PERSONS:
                cursor = db.query("persons", projection, selection, selectionArgs, null, null, sortOrder);
                break;
            case PERSON_ID:
                String id = uri.getPathSegments().get(1);
                cursor = db.query("persons", projection, "id=?", new String[]{id}, null, null, sortOrder);
                break;
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
        return cursor;
    }

    @Nullable
    @Override
    public String getType(Uri uri) {
        switch (uriMatcher.match(uri)) {
            case PERSONS:
                return "vnd.android.cursor.dir/persons";
            case PERSON_ID:
                return "vnd.android.cursor.item/person";
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
    }

    @Nullable
    @Override
    public Uri insert(Uri uri, ContentValues values) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        Uri uriReturn = null;
        switch (uriMatcher.match(uri)) {
            case PERSONS:
            case PERSON_ID:
                long newId = db.insert("persons", null, values);
                uriReturn = Uri.parse("content://com.example.myapp.provider/persons/" + newId);
                break;
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
        return uriReturn;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        int count = 0;
        switch (uriMatcher.match(uri)) {
            case PERSONS:
                count = db.delete("persons", selection, selectionArgs);
                break;
            case PERSON_ID:
                String id = uri.getPathSegments().get(1);
                count = db.delete("persons", "id=?", new String[]{id});
                break;
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
        return count;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        int count = 0;
        switch (uriMatcher.match(uri)) {
            case PERSONS:
                count = db.update("persons", values, selection, selectionArgs);
                break;
            case PERSON_ID:
                String id = uri.getPathSegments().get(1);
                count = db.update("persons", values, "id=?", new String[]{id});
                break;
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
        return count;
    }
}

2. 创建数据库类

public class MyDatabaseHelper extends SQLiteOpenHelper {

    private static final String CREATE_PERSONS = "create table persons ("
            + "id integer primary key autoincrement, "
            + "name text, "
            + "age integer)";

    public MyDatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_PERSONS);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

3. 在AndroidManifest.xml中添加ContentProvider

<provider
    android:name=".MyContentProvider"
    android:authorities="com.example.myapp.provider"
    android:exported="true" />

4. 使用ContentProvider

Uri uri = Uri.parse("content://com.example.myapp.provider/persons");
ContentResolver resolver = getContentResolver();
Cursor cursor = resolver.query(uri, new String[]{"id", "name", "age"}, null, null, null);
if (cursor != null) {
    while (cursor.moveToNext()) {
        int id = cursor.getInt(cursor.getColumnIndex("id"));
        String name = cursor.getString(cursor.getColumnIndex("name"));
        int age = cursor.getInt(cursor.getColumnIndex("age"));
        Log.d(TAG, "id=" + id + ", name=" + name + ", age=" + age);
    }
    cursor.close();
}

以上就是一个简单的ContentProvider案例，通过这个案例可以学习如何创建和使用ContentProvider。