Question

您好我正在使用此代码

    Cursor mCursor = this.getContentResolver().query(PlayerContentProviderDB.CONTENT_URI, PLAYERS_PROJECTION, null, null, Players.SCORE + " ASC" + " LIMIT 2");
    this.adapter = new SimpleCursorAdapter(this, R.layout.high_score, mCursor, dataColumns, viewIDs, 0);
    setListAdapter(adapter);

_

@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
    // System.out.println(sortOrder);
    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
    checkColumns(projection);
    queryBuilder.setTables(PlayerContract.Players.PLAYERS_TABLE_NAME);
    int uriType = sURIMatcher.match(uri);

    switch (uriType) {
    case ALL_SCORES:
        break;
    case SCORE_ID:
        queryBuilder.appendWhere(PlayerContract.Players.ID + "=" + uri.getLastPathSegment());
        break;
    default:
        throw new IllegalArgumentException("Unknown URI: " + uri);
    }

    SQLiteDatabase db = this.dbHelper.getReadableDatabase();
    Cursor cursor = queryBuilder.query(db, projection, selection, selectionArgs, null, null, sortOrder);
    System.out.println(uri.toString() + " " + projection[0] + " " + projection[1] + " " + projection[2] + " " + projection[3] + " " + selection + " " + sortOrder);
    // Notify potential listeners
    cursor.setNotificationUri(getContext().getContentResolver(), uri);
    return cursor;
}

尝试排序和限制数据库的返回，但它无法正常工作。通过插入诊断打印语句，我注意到在调用上述代码后立即调用我的内容提供程序的查询方法。我认为这可能与我的错误的根源有关。所以我的问题是为什么我的查询方法被调用两次？

更新

我现在知道我的错误是由于调用两次查询引起的。在第一次调用时，我的字符串顺序是正确的，但在第二次调用时它是null，这使得我的列表未分类且无限制。

我的ListView链接到新活动

    setListAdapter(new ArrayAdapter<String>(this, R.layout.puzzle_selector, options));

    ListView list = this.getListView();
    list.setTextFilterEnabled(true);
    list.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            if (!((TextView) view).getText().toString().equalsIgnoreCase("HighScore")) {
                String selectionString[] = ((TextView) view).getText().toString().split(" ");
                String puzzleNumber = selectionString[1];
                System.out.println("puzzleNumber is " + puzzleNumber);

                SharedPreferences prefs = getSharedPreferences(getString(R.string.currentSave), MODE_PRIVATE);
                SharedPreferences.Editor editor = prefs.edit();
                editor.putString("selectedNumber", puzzleNumber);
                editor.commit();

                Intent passPuzzleNumberIntent = new Intent(PuzzleSelector.this, MainActivity.class);
                passPuzzleNumberIntent.putExtra("puzzleNumber", puzzleNumber);
                startActivity(passPuzzleNumberIntent);
            } else {
                Intent lookAtScoresIntent = new Intent(PuzzleSelector.this, HighScores.class);
                startActivity(lookAtScoresIntent);
            }
        }
    });

Answer 1

由于列表视图布局两次，一次没有高度，再次设置高度后（在Android中常见），getView在与适配器关联的列表上被调用两次。为了确保您不会多次在列表视图中布置个体视图，请检查视图是否为null，如果是，则将其放在方法getView中：

public View getView(int position, View convertView, ViewGroup parent) {
    super.getView(position, convertView, parent);

    if (convertView == null) {
        // do custom layout of view with data from cursor
    }

    return convertView;
}

为什么查询被调用两次？

1 个答案: