c# - WPF 切换 UIElements 在 DataTemplate 中的可见性

Question

我有一个 DataTemplate 定义如下

<DataTemplate x:Key="PasswordViewerTemplate">
  <StackPanel>
    <TextBlock Text="{Binding PasswordChar, ElementName=this}"
               Visibility="Visible" />
    <TextBox Text="{Binding PasswordText}"
             Visibility="Collapsed" />
  </StackPanel>
</DataTemplate>

每次用户单击 StackPanel 时，我希望能够切换 TextBlock 和 TextBox 的可见性。我尝试在 StackPanel 上设置一个 MouseLeftButtonUp 事件处理程序，但这会引发异常

Object reference not set to an instance of an object

还有其他方法可以实现吗？也许在 XAML 本身中使用触发器？

此外，这可能是相关的。上面的模板是模板选择器应用于 ListBox 的两个模板之一。 ListBox 本身位于 Grid 中，并且两个模板都在 Grid.Resources 部分中定义。

编辑 1
我尝试如下设置事件

<StackPanel MouseLeftButtonUp="OnPasswordViewerMouseLeftButtonUp">
...
</StackPanel>

private void OnPasswordViewerMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
  var sp = sender as StackPanel;
  if( ( sp == null ) || ( sp.Children.Count != 2 ) ) {
    return;
  }

  var passwordText = sp.Children[0] as TextBlock;
  var plainText = sp.Children[1] as TextBox;
  if( ( passwordText == null ) || ( plainText == null ) ) {
    return;
  }

  passwordText.Visibility = ( passwordText.Visibility == Visibility.Visible ) ? 
    Visibility.Collapsed : Visibility.Visible;
  plainText.Visibility = ( plainText.Visibility == Visibility.Visible ) ?
    Visibility.Collapsed : Visibility.Visible;
}

Answer 1

解决方案之一是将 TextBox 和 TextBlock 的可见性绑定(bind)到用作 DataContext 的类的属性 堆栈面板。这是一个示例实现:

Xaml代码:

<Grid>
    <Grid.Resources>
        <DataTemplate x:Key="PasswordViewerTemplate">
            <StackPanel PreviewMouseUp="StackPanel_PreviewMouseUp">
                <TextBlock Text="{Binding Path=PasswordChar}"
           Visibility="{Binding Path=TextBlockVisibility}" />
                <TextBox Text="{Binding Path=PasswordText}"
         Visibility="{Binding Path=TextBoxVisibility}" />
            </StackPanel>
        </DataTemplate>
    </Grid.Resources>
    <ListBox x:Name="lbox" ItemTemplate="{StaticResource ResourceKey=PasswordViewerTemplate}" ItemsSource="{Binding}"/>
</Grid>

和C#代码:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        ObservableCollection<Some> items = new ObservableCollection<Some>();
        for (int i = 0; i < 10; i++)
        {
            items.Add(new Some(string.Format("passwordChar {0}", i + 1), string.Format("passwordText {0}", i + 1), Visibility.Visible, Visibility.Collapsed));
        }
        this.lbox.ItemsSource = items;
    }

    private void StackPanel_PreviewMouseUp(object sender, MouseButtonEventArgs e)
    {
        Some some = (sender as StackPanel).DataContext as Some;
        some.TextBlockVisibility = ToggleVisibility(some.TextBlockVisibility);
        some.TextBoxVisibility = ToggleVisibility(some.TextBoxVisibility);
    }
    private Visibility ToggleVisibility(Visibility visibility)
    {
        return visibility == Visibility.Visible ? Visibility.Collapsed : Visibility.Visible;
    }
}
public class Some:INotifyPropertyChanged
{
    private string _passwordChar;
    private string _passwordText;
    private Visibility _textBlockVisibility, _textBoxVisibility;

    public string PasswordChar { get { return this._passwordChar; } set { this._passwordChar = value; } }
    public string PasswordText { get { return this._passwordText; } set { this._passwordText = value; } }
    public Visibility TextBlockVisibility 
    { 
        get { return this._textBlockVisibility; } 
        set 
        { 
            this._textBlockVisibility = value;
            RaisePropertyChanged("TextBlockVisibility");
        }

    }
    public Visibility TextBoxVisibility 
    { 
        get { return this._textBoxVisibility; }
        set 
        { 
            this._textBoxVisibility = value;
            RaisePropertyChanged("TextBoxVisibility");
        }
    }

    public Some(string passwordChar, string passwordText, Visibility textBlockVisibility, Visibility textBoxVisibility)
    {
        this._passwordChar = passwordChar;
        this._passwordText = passwordText;
        this._textBlockVisibility = textBlockVisibility;
        this._textBoxVisibility = textBoxVisibility;
    }


    public event PropertyChangedEventHandler PropertyChanged;
    protected void RaisePropertyChanged(string name)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(name));
    }
}