Android - 在contentProvider中选择最大值

Question

我尝试在我的自定义内容提供者上运行此查询.

cursor = activity.getContentResolver().query(
                GoalDescriptor.CONTENT_URI,
                "max(priority)", null,
                null, null);

获取优先级int列的最大值.

我也尝试过:

cursor = activity.getContentResolver().query(
                GoalDescriptor.CONTENT_URI,
                null, "max(priority)",
                null, null);

没有成功.

此代码返回此异常:

    java.lang.IllegalArgumentException: Invalid column MAX(priority)
E/DatabaseUtils(  688):     at android.database.sqlite.SQLiteQueryBuilder.computeProjection(SQLiteQueryBuilder.java:523)
E/DatabaseUtils(  688):     at android.database.sqlite.SQLiteQueryBuilder.buildQuery(SQLiteQueryBuilder.java:370)
E/DatabaseUtils(  688):     at android.database.sqlite.SQLiteQueryBuilder.query(SQLiteQueryBuilder.java:323)
E/DatabaseUtils(  688):     at android.database.sqlite.SQLiteQueryBuilder.query(SQLiteQueryBuilder.java:280)
E/DatabaseUtils(  688):     at nan.salsa.contentprovider.goal.GoalContentProvider.query(GoalContentProvider.java:118)
E/DatabaseUtils(  688):     at android.content.ContentProvider$Transport.bulkQuery(ContentProvider.java:150)
E/DatabaseUtils(  688):     at android.content.ContentProviderNative.onTransact(ContentProviderNative.java:111)
E/DatabaseUtils(  688):     at android.os.Binder.execTransact(Binder.java:288)
E/DatabaseUtils(  688):     at dalvik.system.NativeStart.run(Native Method)
D/AndroidRuntime(  727): Shutting down VM

我的内容提供商实施(标准 - 请参阅notePad示例)

public Cursor query(Uri uri, String[] projection, String selection,
        String[] selectionArgs, String sortOrder) {
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
    qb.setTables(GoalDescriptor.TABLE_NAME);

    switch (sUriMatcher.match(uri)) {

    case GOAL:
        qb.setProjectionMap(sGoalProjectionMap);
        qb.appendWhere(GoalDescriptor._ID + "="
                + uri.getPathSegments().get(1));
        break;

    case GOALS:
        qb.setProjectionMap(sGoalProjectionMap);
        break;

    default:
        throw new IllegalArgumentException("Unknown URI " + uri);
    }

    // If no sort order is specified use the default
    String orderBy;
    if (TextUtils.isEmpty(sortOrder)) {
        orderBy = GoalInfo.GoalDescriptor.DEFAULT_SORT_ORDER;
    } else {
        orderBy = sortOrder;
    }

    // Get the database and run the query
    SQLiteDatabase db = mOpenHelper.getReadableDatabase();
    Cursor c = qb.query(db, projection, selection, selectionArgs, null,
            null, orderBy);

    // Tell the cursor what uri to watch, so it knows when its source data
    // changes
    c.setNotificationUri(getContext().getContentResolver(), uri);
    return c;
}

你能帮助我吗 ？

问候

Answer 1

您正在发送最大(优先级)作为投影,将其作为选择发送,它应该工作.

看到这个问题: Android:获取列中的最高价值

编辑:

它似乎应该工作:

cursor = activity.getContentResolver().query(
         GoalDescriptor.CONTENT_URI,
          new String[] {"MAX(priority) AS max_priority"}, null,
         null, null);