wpf 使用 ItemsSource 时操作无效。使用 ItemsControl.ItemsSource 访问和修改元素

Operation is not valid while ItemsSource is in use. Access and modify elements with ItemsControl.ItemsSource

提问by kknaguib

I'm trying to make 2 list boxes where I can press on a button to add an item selected from the left listbox to the right listbox. Here's the XAML for the listboxes:

我正在尝试制作 2 个列表框，我可以在其中按一个按钮将从左侧列表框中选择的项目添加到右侧列表框中。这是列表框的 XAML：

        <ListBox
        x:Name="LeftList"
        Foreground="{StaticResource Foreground}"
        HorizontalAlignment="Left" 
        Height="237" Margin="15,103,0,0" 
        VerticalAlignment="Top" 
        Width="128">
        <ListBoxItem>360T</ListBoxItem>
        <ListBoxItem>BARX</ListBoxItem>
        <ListBoxItem>BNP</ListBoxItem>
        <ListBoxItem>BOA</ListBoxItem>
        <ListBoxItem>CITI</ListBoxItem>
        <ListBoxItem>CS</ListBoxItem>
        <ListBoxItem>DB</ListBoxItem>
        <ListBoxItem>GS</ListBoxItem>
        <ListBoxItem>JPM</ListBoxItem>
        <ListBoxItem>RBS</ListBoxItem>
        <ListBoxItem>UBS</ListBoxItem>
    </ListBox>

    <ListBox 
        x:Name="RightList"
        Foreground="{StaticResource Foreground}"
        HorizontalAlignment="Left" 
        Height="237" Margin="257,103,0,0" 
        VerticalAlignment="Top" 
        Width="128"/>

C#:

C＃：

List<string> leftSideList = new List<string>();
List<string> rightSideList = new List<string>();

    public ChooseLPWindow()
    {
        InitializeComponent();

        //Add to the collection leftside list
        leftSideList.Add("360T");
        leftSideList.Add("BARX");
        leftSideList.Add("BNP");
        leftSideList.Add("BOA");
        leftSideList.Add("CITI");
        leftSideList.Add("CS");
        leftSideList.Add("DB");
        leftSideList.Add("GS");
        leftSideList.Add("JPM");
        leftSideList.Add("RBS");
        leftSideList.Add("UBS");

    }

    private void AddBtn_Click(object sender, RoutedEventArgs e)
    {
        if (LeftList.SelectedIndex > -1)
        {
            int SelectedIndex = LeftList.SelectedIndex;
            string SelectedItem = LeftList.SelectedValue.ToString();

            //Add the selected item to the right side list
            RightList.Items.Add(SelectedItem);
            rightSideList.Add(SelectedItem);

            if (leftSideList != null)
            {
                //Remove the item from the collection list 
                leftSideList.RemoveAt(SelectedIndex);

                //Update the left side list
                LeftList.Items.Clear();
                LeftList.ItemsSource = leftSideList;
            }
        }
    }

I get the exception on:

我得到以下异常：

LeftList.Items.Clear();

This happens when I try to add a second item the first one gets added but then the exception occurs when you try to add another item. The error is:

当我尝试添加第二个项目时会发生这种情况，第一个项目被添加，但是当您尝试添加另一个项目时会发生异常。错误是：

Operation is not valid while ItemsSource is in use. Access and modify elements with ItemsControl.ItemsSource

使用 ItemsSource 时操作无效。使用 ItemsControl.ItemsSource 访问和修改元素

Any suggestions?

有什么建议？

回答by har07

You can't modify ListBox's Itemswhen the items populated through ItemsSource. In that case you suppose to modify items in the ItemsSourcecollection instead.

您不能修改ListBox的Items当物品填充通过ItemsSource。在这种情况下，您应该改为修改ItemsSource集合中的项目。

I'd suggest to change your Listto ObservableCollection. With that removing item from collection is enough, because ObservableCollectionhas built-in mechanism to notify UI to refresh whenever item added or removed from collection :

我建议将您的更改List为ObservableCollection. 有了从集合中删除项目就足够了，因为ObservableCollection有内置机制来通知 UI 在从集合中添加或删除项目时刷新：

ObservableCollection<string> leftSideList = new ObservableCollection<string>();
ObservableCollection<string> rightSideList = new ObservableCollection<string>();

public ChooseLPWindow()
{
    InitializeComponent();

    leftSideList.Add("360T");
    leftSideList.Add("BARX");
    leftSideList.Add("BNP");
    leftSideList.Add("BOA");
    leftSideList.Add("CITI");
    leftSideList.Add("CS");
    leftSideList.Add("DB");
    leftSideList.Add("GS");
    leftSideList.Add("JPM");
    leftSideList.Add("RBS");
    leftSideList.Add("UBS");

    LeftList.ItemsSource = leftSideList;
}

private void AddBtn_Click(object sender, RoutedEventArgs e)
{
    if (LeftList.SelectedIndex > -1)
    {
        int SelectedIndex = LeftList.SelectedIndex;
        string SelectedItem = LeftList.SelectedValue.ToString();

        //Add the selected item to the right side list
        RightList.Items.Add(SelectedItem);
        rightSideList.Add(SelectedItem);

        if (leftSideList != null)
        {
            //Remove the item from the ItemsSource collection 
            //instead of removing it from ListBox.Items
            leftSideList.RemoveAt(SelectedIndex);
        }
    }
}

回答by kknaguib

I fixed the issue by doing this:

我通过这样做解决了这个问题：

    private void AddBtn_Click(object sender, RoutedEventArgs e)
    {
        if (LeftList.SelectedIndex > -1)
        {
            int SelectedIndex = LeftList.SelectedIndex;
            string SelectedItem = LeftList.SelectedValue.ToString();

            //Add the selected item to the right side list
            RightList.Items.Add(SelectedItem);
            rightSideList.Add(SelectedItem);

            //Delete the item from the left side list
            //ListLps.Items.RemoveAt(SelectedIndex);

            if (leftSideList != null)
            {
                //Remove the item from the collection list 
                leftSideList.RemoveAt(SelectedIndex);
                LeftList.Items.RemoveAt(SelectedIndex);

            }
        }

    }