android studio 内容提供者例子

Android Studio中的内容提供者示例可以通过以下步骤实现：
1. 创建一个新项目并在其中创建一个新的Java类。
2. 在Java类中实现ContentProvider类，并重写其方法以提供数据的增删改查功能。
3. 在AndroidManifest.xml文件中注册ContentProvider类。
4. 在应用程序中使用ContentResolver对象来访问ContentProvider中的数据。

以下是一个简单的示例代码，演示如何创建一个ContentProvider类并实现其方法：

public class MyContentProvider extends ContentProvider {
    private static final String AUTHORITY = "com.example.myapp.provider";
    private static final String BASE_PATH = "mydata";
    public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/" + BASE_PATH);

    private SQLiteDatabase database;

    @Override
    public boolean onCreate() {
        DBHelper dbHelper = new DBHelper(getContext());
        database = dbHelper.getWritableDatabase();
        return true;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
        SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
        queryBuilder.setTables(MyTable.TABLE_NAME);

        int uriType = sURIMatcher.match(uri);
        switch (uriType) {
            case MYDATA:
                break;
            case MYDATA_ID:
                queryBuilder.appendWhere(MyTable.COLUMN_ID + "=" + uri.getLastPathSegment());
                break;
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }

        Cursor cursor = queryBuilder.query(database, projection, selection, selectionArgs, null, null, sortOrder);
        cursor.setNotificationUri(getContext().getContentResolver(), uri);
        return cursor;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        int uriType = sURIMatcher.match(uri);
        long id = 0;
        switch (uriType) {
            case MYDATA:
                id = database.insert(MyTable.TABLE_NAME, null, values);
                break;
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
        getContext().getContentResolver().notifyChange(uri, null);
        return Uri.parse(BASE_PATH + "/" + id);
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        int uriType = sURIMatcher.match(uri);
        int rowsDeleted = 0;
        switch (uriType) {
            case MYDATA:
                rowsDeleted = database.delete(MyTable.TABLE_NAME, selection, selectionArgs);
                break;
            case MYDATA_ID:
                String id = uri.getLastPathSegment();
                if (TextUtils.isEmpty(selection)) {
                    rowsDeleted = database.delete(MyTable.TABLE_NAME, MyTable.COLUMN_ID + "=" + id, null);
                } else {
                    rowsDeleted = database.delete(MyTable.TABLE_NAME, MyTable.COLUMN_ID + "=" + id + " and " + selection, selectionArgs);
                }
                break;
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
        getContext().getContentResolver().notifyChange(uri, null);
        return rowsDeleted;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        int uriType = sURIMatcher.match(uri);
        int rowsUpdated = 0;
        switch (uriType) {
            case MYDATA:
                rowsUpdated = database.update(MyTable.TABLE_NAME, values, selection, selectionArgs);
                break;            case MYDATA_ID:
                String id = uri.getLastPathSegment();
                if (TextUtils.isEmpty(selection)) {
                    rowsUpdated = database.update(MyTable.TABLE_NAME, values, MyTable.COLUMN_ID + "=" + id, null);
                } else {
                    rowsUpdated = database.update(MyTable.TABLE_NAME, values, MyTable.COLUMN_ID + "=" + id + " and " + selection, selectionArgs);
                }
                break;
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
        getContext().getContentResolver().notifyChange(uri, null);
        return rowsUpdated;
    }

    private static final UriMatcher sURIMatcher = new UriMatcher(UriMatcher.NO_MATCH);
    private static final int MYDATA = 1;
    private static final int MYDATA_ID = 2;

    static {
        sURIMatcher.addURI(AUTHORITY, BASE_PATH, MYDATA);
        sURIMatcher.addURI(AUTHORITY, BASE_PATH + "/#", MYDATA_ID);
    }
}

在这个示例中，我们创建了一个名为MyContentProvider的ContentProvider类，并实现了其query、insert、delete和update方法。我们还在AndroidManifest.xml文件中注册了MyContentProvider类，并在应用程序中使用ContentResolver对象来访问ContentProvider中的数据。