Question

每当将一个项添加到ObservableCollection时，我都会尝试自动选择ListView中的项。我正在使用CollectionChanged事件来监听添加项目的时间，然后选择它。 CollectionChanged事件似乎在UI更新之前发生，因此SelectedIndex会相应调整。我已经尝试设置SelectedIndex和SelectedItem，但在两种情况下，添加的项目最终都被选中。正确的索引是更改集合的时间，UI更新，然后ListView增加索引。

这种现象可以用以下方式证明：

<Window x:Class="WpfApplication2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" DataContext="{Binding Main, Source= {StaticResource Locator}}">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="30"/>
        </Grid.RowDefinitions>
        <ListView ItemsSource="{Binding Items, Mode=TwoWay}" SelectedItem="{Binding SelectedItem, Mode=TwoWay}" SelectedIndex="{Binding SelectedIndex, Mode=TwoWay}" Grid.Row="0">
        </ListView>
        <StackPanel Orientation="Horizontal" Grid.Row="1">
            <Button Content="Add Item" Width="75" Command="{Binding AddItemCommand}"/>
            <Label Content="SelectedIndex:"/>
            <Label Content="{Binding SelectedIndex}"/>
            <Label Content="SelectedItem:"/>
            <Label Content="{Binding SelectedItem}"/>
            <Label Content="&lt;- Numbers should match after item added"/>
        </StackPanel>
    </Grid>
</Window>

和ViewModel：

public class MainViewModel : ViewModelBase
{
    private ICommand addItemCommand;
    /// <summary>
    /// Initializes a new instance of the MainViewModel class.
    /// </summary>
    public MainViewModel()
    {
        Items = new ObservableCollection<string>();
        Items.CollectionChanged += Items_CollectionChanged;
    }

    private int selectedIndex = -1;
    public const string SelectedIndexPropertyName = "SelectedIndex";
    public int SelectedIndex
    {
        get
        {
            return selectedIndex;
        }
        set
        {
            if (selectedIndex != value)
            {
                selectedIndex = value;
                RaisePropertyChanged(SelectedIndexPropertyName);
            }
        }
    }

    private string selectedItem = null;
    public const string SelectedItemPropertyName = "SelectedItem";
    public string SelectedItem
    {
        get
        {
            return selectedItem;
        }
        set
        {
            if (selectedItem != value)
            {
                selectedItem = value;
                RaisePropertyChanged(SelectedItemPropertyName);
            }
        }
    }

    private ObservableCollection<string> items;
    public const string ItemsPropertyName = "Items";
    public ObservableCollection<string> Items
    {
        get
        {
            return items;
        }
        set
        {
            items = value;
            RaisePropertyChanged(ItemsPropertyName);
        }
    }

    private void Items_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Add)
        {
            //SelectedItem = e.NewItems[0];
            SelectedIndex = e.NewStartingIndex;
        }
    }

    public ICommand AddItemCommand
    {
        get
        {
            if (addItemCommand == null)
                addItemCommand = new RelayCommand(() => Items.Add("Item " + items.Count));

            return addItemCommand;
        }
    }
}

我已将上传的示例解决方案添加到www.itzalive.co.uk/AddItemSelection.zip

有人知道如何最终使用CollectionChanged事件选择新添加的项目吗？在我的实际程序中，项目未添加到显示的相同位置，因此无法单独设置所选项目。

Answer 1

最好只使用SelectedItem属性，而不是SelectedIndex属性：

<ListView ItemsSource="{Binding Items, Mode=TwoWay}" 
    SelectedItem="{Binding SelectedItem, Mode=TwoWay}" ... />

然后在代码中：

YourClass newItem = new YourClass();
Items.Add(newItem);
SelectedItem = newItem;

还要从Items_CollectionChanged事件处理程序中删除您的代码。您可能还需要调用NotifyPropertyChanged("Items");来更新UI（如果尚未更新）。

更新＆gt;＆gt;＆gt;

尝试将此添加到您的CollectionChanged处理程序中：

if (e.Action == NotifyCollectionChangedAction.Add) 
    SelectedItem = e.NewItems[0] as string;

自动选择添加到ObservableCollection的项目

1 个答案: