java - Arraylist 无法与游标查询一起正常工作

Question

我有一个游标，它从下面的数据库查询中返回 5 个最新结果。

    public Cursor totaldistance(){
    String[] columns = new String[] { DatabaseHelper._ID, DatabaseHelper.DSNM, DatabaseHelper.SDATE };
    Cursor cursor = database.query(DatabaseHelper.TABLE_NAME, columns, null, null, null, null, DatabaseHelper._ID + " DESC limit 5");
    if (cursor != null) {
        cursor.moveToFirst();
    }
    return cursor;
}

然后我将返回的游标值分配给下面的数组列表。它工作正常，接受 arrayList 缺少最新的数据库记录值。例如，我可以在数据库中有 4 个值，但第二个最新值被分配给数组列表中的位置 0。我不确定是我的游标查询还是 while 语句有问题。有人知道吗？谢谢!

        List<String> distancearray = new ArrayList<String>();
    distancearray.add("0");
    distancearray.add("0");
    distancearray.add("0");
    distancearray.add("0");
    distancearray.add("0");
    int i = 0;

    while(DistanceArray.moveToNext()){
        String uname = DistanceArray.getString(DistanceArray.getColumnIndex("distance"));

        distancearray.set(i, uname);
        i++;
    }

根据下面的建议，我更新了我的代码。它现在正在从数据库中检索第一个结果，但不会循环遍历下一个 4。运行下面的代码后，我的 arraylist 应该读取 10,8,6,1,0，但实际结果是 10,10,10,10 ,0.它正在重复第一个检索到的值。如何修复 do while 操作以将正确的结果写入数组？谢谢!

        List<String> distancearray = new ArrayList<String>();
    distancearray.add(0, "0");
    distancearray.add(1, "0");
    distancearray.add(2, "0");
    distancearray.add(3, "0");
    distancearray.add(4, "0");
    Cursor cursor =  dbManager.totaldistance();
    do{
        String uname = DistanceArray.getString(DistanceArray.getColumnIndex("distance"));
        distancearray.set(i, uname);
        Log.i("Graph", "Value i = " + i);
        Log.i("Graph", "Array value = " + uname);
        i++;
    }while ((cursor.moveToNext()));

Answer 1

我认为您在调用 cursor.moveToFirst(); 时“丢失”了一行

public Cursor totaldistance(){
    String[] columns = new String[] { DatabaseHelper._ID, DatabaseHelper.DSNM, DatabaseHelper.SDATE };
    Cursor cursor = database.query(DatabaseHelper.TABLE_NAME, columns, null, null, null, null, DatabaseHelper._ID + " DESC limit 5");
    if (cursor != null) {
        // Here you are pointing to the first row of the cursor
        // you need to add this row content into your list  
        cursor.moveToFirst();
    }
    return cursor;
}

因此，当您在上一个方法中调用 moveToFirs() 时，将所有行添加到列表的代码应如下所示

List<String> distancearray = new ArrayList<String>();
Cursor cursor =  dbManager.totaldistance();
do{
    distancearray.add(cursor.getString(cursor.getColumnIndex("distance")));
}while ((cursor.moveToNext()));

// Be sure here to have at least the 5 desired elements into the list
while(distancearray.size() < 5){
    distancearray.add("0");
}