在WPF列表框中上下移动项目

Question

我有一个列表框,里面有一堆值.我还有一个UP按钮和一个DOWN按钮.使用这些按钮,我想向上/向下移动列表框中的所选项目.我这样做有困难.

到目前为止,这是我的代码:

    private void btnDataUp_Click(object sender, RoutedEventArgs e)
    {

        int selectedIndex = listBoxDatasetValues.SelectedIndex; //get the selected item in the data list

        if (selectedIndex != -1 && selectedIndex != 0) //if the selected item is selected and not at the top of the list
        {
            //swap items here
            listBoxDatasetValues.SelectedIndex = selectedIndex - 1; //keep the item selected
        }


    }

我不知道如何交换价值观!任何帮助将不胜感激!

Answer 1

由于您已使用ItemsSource通过绑定到ObservableCollection来填充列表框,因此您无法修改列表框的Items属性.

ItemsSource只能在Items集合为空时设置,并且只有在ItemsSource为null时才能修改Items.

否则,您将收到错误"当ItemsSource正在使用时操作无效..."

你需要做的是修改底层集合,因为它是一个ObservableCollection,ListBox将反映这些变化.

以下代码显示了如何通过交换集合中的项目来上下移动项目.

相应的XAML只包含一个名为lbItems的列表框和两个用于连接事件处理程序的按钮.

public partial class MainWindow : Window
{
    private ObservableCollection<string> ListItems = new ObservableCollection<string>  
    { 
        "Item 1", "Item 2", "Item 3", "Item 4", "Item 5", "Item 6"
    };

    public MainWindow()
    {
        InitializeComponent();
        lbItems.ItemsSource = this.ListItems;
    }

    private void up_click(object sender, RoutedEventArgs e)
    {
        var selectedIndex = this.lbItems.SelectedIndex;

        if (selectedIndex > 0)
        {
            var itemToMoveUp = this.ListItems[selectedIndex];
            this.ListItems.RemoveAt(selectedIndex);
            this.ListItems.Insert(selectedIndex - 1, itemToMoveUp);
            this.lbItems.SelectedIndex = selectedIndex - 1;
        }
    }

    private void down_click(object sender, RoutedEventArgs e)
    {
        var selectedIndex = this.lbItems.SelectedIndex;

        if (selectedIndex + 1 < this.ListItems.Count)
        {
            var itemToMoveDown = this.ListItems[selectedIndex];
            this.ListItems.RemoveAt(selectedIndex);
            this.ListItems.Insert(selectedIndex + 1, itemToMoveDown);
            this.lbItems.SelectedIndex = selectedIndex + 1;
        }
    }
}

Answer 2

我为此做了一些扩展方法:

    public static void MoveItemUp<T>(this ObservableCollection<T> baseCollection, int selectedIndex)
    {
        //# Check if move is possible
        if (selectedIndex <= 0)
            return;

        //# Move-Item
        baseCollection.Move(selectedIndex - 1, selectedIndex);
    }

    public static void MoveItemDown<T>(this ObservableCollection<T> baseCollection, int selectedIndex)
    {
        //# Check if move is possible
        if (selectedIndex < 0 || selectedIndex + 1 >= baseCollection.Count)
            return;

        //# Move-Item
        baseCollection.Move(selectedIndex + 1, selectedIndex);
    }

    public static void MoveItemDown<T>(this ObservableCollection<T> baseCollection, T selectedItem)
    {
        //# MoveDown based on Item
        baseCollection.MoveItemDown(baseCollection.IndexOf(selectedItem));
    }

    public static void MoveItemUp<T>(this ObservableCollection<T> baseCollection, T selectedItem)
    {
        //# MoveUp based on Item
        baseCollection.MoveItemUp(baseCollection.IndexOf(selectedItem));
    }

没有必要知道ListBox.

Answer 3

这是执行此操作的最简单方法，它会触发所有正确的事件，因此您不必担心 XAML。ObservableCollection 有一个很好的方法叫做

MoveItem(previousIndex, newIndex)

鉴于您有一个名为 DataItemList 的 ObservableCollection

public void MoveUp()
{
  var currentIndex = DataItemList.SelectedIndex;

  //Index of the selected item
  if (currentIndex > 0)
  {
    int upIndex = currentIndex - 1;

    //move the items
    DataItemList.MoveItem(upIndex,currentIndex);         
  }
}

对于 Down，您将获得前一项的索引。

就那么简单！