WPF：雙向數據綁定不起作用

Question

我發現了一些類似的問題，但這些並不是我所需要的。 我想將堆棧面板“IsEnabled”值綁定到我的項目的布爾值“！IsIterrupted”。 這是我的 XAML 文件：

<ListView ItemsSource="{Binding Path=Items}">
        <ListView.ItemTemplate>
            <DataTemplate>
                <StackPanel IsEnabled="{Binding !IsInterrupted, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}">
                    <Button Command="{Binding Path=StopThreadCommand, Source={StaticResource viewModel}}" CommandParameter="{Binding Id}"/>
                </StackPanel>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>

這是項目的樣子：

public class ThreadDecorator : BaseThread , INotifyPropertyChanged
{
    ...
    public event PropertyChangedEventHandler PropertyChanged;

    private bool _is_interrupted;
    public bool IsInterrupted
    {
        get { return _is_interrupted; }
        set
        {
            _is_interrupted = value;
            OnPropertyChanged("IsInterrupted");
        }
    }

    protected virtual void OnPropertyChanged(string propertyName)
    {
        if (this.PropertyChanged != null)
        {
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
    ...
}

還有我的視圖模型：

public class ThreadsViewModel : DependencyObject
{

    private ThreadsModel _model;
    public ThreadsModel Model
    {
        get { return _model; }
        set
        {
            _model = value;
        }
    }

    public ICollectionView Items
    {
        get { return (ICollectionView)GetValue(ItemsProperty); }
        set { SetValue(ItemsProperty, value); }
    }

    public static readonly DependencyProperty ItemsProperty =
        DependencyProperty.Register("Items", typeof(ICollectionView), typeof(ThreadsViewModel), new PropertyMetadata(null));

    public StopThreadCommand StopThreadCommand { get; set; }

    public ThreadsViewModel()
    {
        this.Model = new ThreadsModel();
        Items = CollectionViewSource.GetDefaultView(Model.Threads);
        this.StopThreadCommand = new StopThreadCommand(this);
    }

    public void InterruptThread(int id)
    {
        _model.InterruptThread(id);
    }
}

停止線程命令：

public class StopThreadCommand : ICommand
{
    public ThreadsViewModel ViewModel {get; set;}
    public StopThreadCommand(ThreadsViewModel viewModel)
    {
        this.ViewModel = viewModel;
    }

    public bool CanExecute(object parameter)
    {
        return true;
    }

    public void Execute(object parameter)
    {
        this.ViewModel.InterruptThread((int)parameter);
    }
}

當我單擊“停止”按鈕時，IsInterrupted 值從 false 變為 true，並且必須禁用堆棧面板，但 UI 不會更新。 請幫忙！

Answer 1

Binding的默認屬性是Path ，它是DataContext的屬性/子屬性的路徑。 它不是任意的 C# 表達式。 所以你將Binding.Path設置為"!IsInterrupted" 。 !IsInterrupted不會計算為IsInterrupted的布爾逆； 它不會評估任何東西。 它會在調試輸出流中為您提供：

System.Windows.Data 錯誤：40：BindingExpression 路徑錯誤：在“對象”“ThreadDecorator”上找不到“！IsInterrupted”屬性等等

<StackPanel 
    IsEnabled="{Binding !IsInterrupted, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}">

一種方法是編寫一個布爾值-逆值轉換器（從該鏈接另一端的 Chris Nicol 的回答中逐字竊取）：

[ValueConversion(typeof(bool), typeof(bool))]
public class InverseBooleanConverter: IValueConverter
{
    #region IValueConverter Members

    public object Convert(object value, Type targetType, object parameter,
        System.Globalization.CultureInfo culture)
    {
        if (targetType != typeof(bool))
            throw new InvalidOperationException("The target must be a boolean");

        return !(bool)value;
    }

    public object ConvertBack(object value, Type targetType, object parameter,
        System.Globalization.CultureInfo culture)
    {
        throw new NotSupportedException();
    }

    #endregion
}

用法：

<UserControl.Resources>
    <local:InverseBooleanConverter x:Key="InverseBooleanConverter" />
</UserControl.Resources>

<!-- stuff etc. -->

IsEnabled="{Binding Path=IsReadOnly, Converter={StaticResource InverseBooleanConverter}}"

您還可以編寫帶有DataTrigger的 Style，如果IsInterrupted為 true，則將IsEnabled設置為False 。