使用MVVM的WPF绑定失败

本文关键字：绑定 失败 WPF MVVM 使用 | 更新日期: 2023-09-27 18:04:41

我已经创建了一个继承自AvalonEdit的自定义TextEditor控件。我这样做是为了方便使用MVVM和Caliburn Micro使用这个编辑器控件。MvvTextEditor类

public class MvvmTextEditor : TextEditor, INotifyPropertyChanged
{
    public MvvmTextEditor()
    {
        TextArea.SelectionChanged += TextArea_SelectionChanged;
    }
    void TextArea_SelectionChanged(object sender, EventArgs e)
    {
        this.SelectionStart = SelectionStart;
        this.SelectionLength = SelectionLength;
    }
    public static readonly DependencyProperty SelectionLengthProperty =
         DependencyProperty.Register("SelectionLength", typeof(int), typeof(MvvmTextEditor),
         new PropertyMetadata((obj, args) =>
             {
                 MvvmTextEditor target = (MvvmTextEditor)obj;
                 target.SelectionLength = (int)args.NewValue;
             }));
    public new int SelectionLength
    {
        get { return base.SelectionLength; }
        set { SetValue(SelectionLengthProperty, value); }
    }
    public event PropertyChangedEventHandler PropertyChanged;
    public void RaisePropertyChanged([CallerMemberName] string caller = null)
    {
        var handler = PropertyChanged;
        if (handler != null)
            PropertyChanged(this, new PropertyChangedEventArgs(caller));
    }
}
现在，在包含该控件的视图中，我有以下XAML: 
    <Controls:MvvmTextEditor 
        Caliburn:Message.Attach="[Event TextChanged] = [Action DocumentChanged()]"
        TextLocation="{Binding TextLocation, Mode=TwoWay}"
        SyntaxHighlighting="{Binding HighlightingDefinition}" 
        SelectionLength="{Binding SelectionLength, 
                                  Mode=TwoWay, 
                                  NotifyOnSourceUpdated=True, 
                                  NotifyOnTargetUpdated=True}" 
        Document="{Binding Document, Mode=TwoWay}"/>

我的问题是SelectionLength(和SelectionStart，但让我们现在只考虑长度，因为问题是相同的)。如果我用鼠标选择了一些东西，从视图到视图模型的绑定工作得很好。现在，我已经编写了一个查找和替换实用程序，我想从后面的代码设置SelectionLength(其中get和set在TextEditor控件中可用)。在我的视图模型中，我只是设置SelectionLength = 50，我在视图模型中实现这一点，如

private int selectionLength;
public int SelectionLength
{
    get { return selectionLength; }
    set
    {
        if (selectionLength == value)
            return;
        selectionLength = value;
        Console.WriteLine(String.Format("Selection Length = {0}", selectionLength));
        NotifyOfPropertyChange(() => SelectionLength);
    }
}

当我设置SelectionLength = 50时，DependencyProperty SelectionLengthProperty不会在MvvmTextEditor类中更新，就像TwoWay绑定到我的控件失败一样，但使用Snoop没有这种迹象。我认为这将只是通过绑定工作，但这似乎并非如此。

是否有一些简单的我错过了，或者我是否必须在MvvmTextEditor类中设置和事件处理程序，侦听我的视图模型中的变化并更新DP本身[这提出了它自己的问题]?

感谢您的宝贵时间。

使用MVVM的WPF绑定失败

这是因为来自DependencyProperty的Getter和Setter只是一个。net包装器。框架将使用GetValue和SetValue本身。

你可以尝试从DependencyProperty访问PropertyChangedCallback，并在那里设置正确的值。

 public int SelectionLength
        {
            get { return (int)GetValue(SelectionLengthProperty); }
            set { SetValue(SelectionLengthProperty, value); }
        }
        // Using a DependencyProperty as the backing store for SelectionLength.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty SelectionLengthProperty =
            DependencyProperty.Register("SelectionLength", typeof(int), typeof(MvvmTextEditor), new PropertyMetadata(0,SelectionLengthPropertyChanged));

        private static void SelectionLengthPropertyChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
        {
            var textEditor = obj as MvvmTextEditor;
            textEditor.SelectionLength = e.NewValue;
        }

如果你仍然开放，这里是另一个答案。由于SelectionLength已经被定义为基类的依赖属性，而不是创建派生类(或向派生类添加已经存在的属性)，因此我将使用附加属性来实现相同的功能。

关键是使用System.ComponentModel.DependencyPropertyDescriptor来订阅已经存在的SelectionLength依赖属性的更改事件，然后在事件处理程序中采取所需的操作。

示例代码:

public class SomeBehavior
{
    public static readonly DependencyProperty IsEnabledProperty
        = DependencyProperty.RegisterAttached("IsEnabled",
        typeof(bool), typeof(SomeBehavior), new PropertyMetadata(OnIsEnabledChanged));
    public static void SetIsEnabled(DependencyObject dpo, bool value)
    {
        dpo.SetValue(IsEnabledProperty, value);
    }
    public static bool GetIsEnabled(DependencyObject dpo)
    {
        return (bool)dpo.GetValue(IsEnabledProperty);
    }
    private static void OnIsEnabledChanged(DependencyObject dpo, DependencyPropertyChangedEventArgs args)
    {
        var editor = dpo as TextEditor;
        if (editor == null)
            return;
        var dpDescriptor = System.ComponentModel.DependencyPropertyDescriptor.FromProperty(TextEditor.SelectionLengthProperty,editor.GetType());
        dpDescriptor.AddValueChanged(editor, OnSelectionLengthChanged);
    }
    private static void OnSelectionLengthChanged(object sender, EventArgs e)
    {
        var editor = (TextEditor)sender;
        editor.Select(editor.SelectionStart, editor.SelectionLength);
    }
}
Xaml如下:

  <Controls:TextEditor Behaviors:SomeBehavior.IsEnabled="True">
    </Controls:TextEditor>

我是这样做的…

public static readonly DependencyProperty SelectionLengthProperty =
     DependencyProperty.Register("SelectionLength", typeof(int), typeof(MvvmTextEditor),
     new PropertyMetadata((obj, args) =>
         {
             MvvmTextEditor target = (MvvmTextEditor)obj;
             if (target.SelectionLength != (int)args.NewValue)
             {
                 target.SelectionLength = (int)args.NewValue;
                 target.Select(target.SelectionStart, (int)args.NewValue);
             }
         }));
public new int SelectionLength
{
    get { return base.SelectionLength; }
    //get { return (int)GetValue(SelectionLengthProperty); }
    set { SetValue(SelectionLengthProperty, value); }
}

很抱歉浪费了你的时间。

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