從游標創建數組

Question

在以下兩種方法中（都覆蓋long[] mArray ），哪種方法更可取？

第一個方法遍歷Cursor ，為每一行調用ArrayList.add() ，然后遍歷ArrayList以將值復制到數組。

第二種方法在Cursor迭代兩次。 一次，每次調用size++來計算行數，然后再次將值復制到數組中。

public void arrayFromCursor1(Cursor cursor) {

    // create a temp ArrayList to add to as we don't
    // know how many rows are in the cursor
    List<Long> list = new ArrayList<Long>();
    // iterate over the cursor
    if (cursor.moveToFirst()) {
        do {
            list.add(cursor.getLong(cursor.getColumnIndex("column_name")));
        } while (cursor.moveToNext());
        // create a long[] of appropriate length and copy values from the
        // ArrayList using a for loop
        final int size = list.size();
        mArray = new long[size];
        for (int i = 0; i < size; i++) {
            mArray[i] = list.get(i);
        }
    }
}

public void arrayFromCursor2(Cursor cursor) {

    // no need for a temp ArrayList this time
    // iterate over the cursor simply counting the rows
    if (cursor.moveToFirst()) {
        int size = 0;
        do {
            size++;
        } while (cursor.moveToNext());
        // create a long[] of appropriate length and iterate over the
        // cursor again, this time with a for loop copying values to the array
        mArray = new long[size];
        cursor.moveToFirst();
        for (int i = 0; i < size; i++) {
            mArray[i] = cursor.getLong(cursor.getColumnIndex("column_name"));
            cursor.moveToNext();
        }
    }
}

Answer 1

我想出了一個從游標創建數組的干凈，簡單的解決方案。 在將數組存儲在外鍵表中時，這很有用，並且可以與基元一起使用。

public long[] arrayFromCursor(Cursor cursor) {

    int length = cursor.getCount();
    long[] array = new long[length];

    if (cursor.moveToFirst()) {
        for (int i = 0; i < length; i++) {
            array[i] = cursor.getLong(cursor.getColumnIndex("column_name"));
            cursor.moveToNext();
        }
    }
    return array;
}