Question

我正在尝试使用MVVM模式的AvalonEdit工作，但我真的不知道该怎么做。我想将SelectionLength和SelectionStart绑定到我的ViewModel，以便在执行某些业务逻辑时可以访问这两个值。

我开始创建像这样的DependencyProperties：

public class MvvmTextEditor : TextEditor, INotifyPropertyChanged
{
    /// <summary>
    /// A bindable Text property
    /// </summary>
    public new string Text
    {
        get { return base.Text; }
        set { 
            base.Text = value; 
            RaisePropertyChanged();
        }
    }

    /// <summary>
    /// A bindable SelectionStart property
    /// </summary>
    public new int SelectionStart
    {
        get { return base.SelectionStart; }
        set {base.SelectionStart = value; }
    }

    /// <summary>
    /// A bindable SelectionLength property
    /// </summary>
    public new int SelectionLength
    {
        get { return base.SelectionLength; }
        set { base.SelectionLength = value; }
    }

    /// <summary>
    /// The bindable selection start property dependency property
    /// </summary>
    public static readonly DependencyProperty SelectionStartProperty =
        DependencyProperty.Register("SelectionStart", typeof(int), typeof(MvvmTextEditor),
            new PropertyMetadata((o, args) =>
            {
                var target = (TextEditor)o;
                target.SelectionStart = (int)args.NewValue;
            }));

    /// <summary>
    /// The bindable selection length property dependency property
    /// </summary>
    public static readonly DependencyProperty SelectionLengthProperty =
        DependencyProperty.Register("SelectionLength", typeof(int), typeof(MvvmTextEditor),
            new PropertyMetadata((o, args) =>
            {
                var target = (MvvmTextEditor) o;

                target.SelectionLength = (int)args.NewValue;
                Debug.WriteLine(target.SelectionLength);

            }));

    /// <summary>
    /// The bindable text property dependency property
    /// </summary>
    public static readonly DependencyProperty TextProperty =
        DependencyProperty.Register("Text", typeof(string), typeof(MvvmTextEditor),
            new PropertyMetadata((o, args) =>
            {
                var target = (MvvmTextEditor)o;
                target.Text = (string)args.NewValue;
            }));

    /// <summary>
    /// Raises a property changed event
    /// </summary>
    /// <param name="property">The name of the property that updates</param>
    public void RaisePropertyChanged([CallerMemberName] string caller = "")
    {
        var handler = PropertyChanged;
        if (handler != null)
            PropertyChanged(this, new PropertyChangedEventArgs(caller));
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

TextDependencyProperty工作正常，但SelectionLength和SelectionStart无效。

我为SelectionChanged添加了一个事件处理程序（但我不完全是我在这里用SetValue做的事情：

    public MvvmTextEditor()
    {
        TextArea.SelectionChanged += TextArea_SelectionChanged;
    }

    void TextArea_SelectionChanged(object sender, EventArgs e)
    {
        SetValue(SelectionStartProperty, SelectionStart);
        SetValue(SelectionLengthProperty, SelectionLength);
    }

选择现在正在运行，但向后选择存在问题。在这种情况下，SelectionStart始终为0.如果一切都是正确的，我到目前为止所做的，那么我将创建一个逻辑，如果有人选择向后，则转换索引和长度是正确的。我是否必须在PropertyMetaDataDelegate中实现此逻辑？

Answer 1

是的，一旦我查看它，原因很明显。在为SelectionStart和SelectionEnd支持DP的属性的setter中，我们设置了base.SelectionStart和base.SelectionLength这创建了这些值的循环更新并阻止了正确从基类更新这些值。更新的MVVM TextEditor类如下所示。

/// <summary>
/// Class that inherits from the AvalonEdit TextEditor control to 
/// enable MVVM interaction. 
/// </summary>
public class MvvmTextEditor : TextEditor, INotifyPropertyChanged
{
    /// <summary>
    /// Default constructor to set up event handlers.
    /// </summary>
    public MvvmTextEditor()
    {
        TextArea.SelectionChanged += TextArea_SelectionChanged;
    }

    /// <summary>
    /// Event handler to update properties based upon the selection changed event.
    /// </summary>
    void TextArea_SelectionChanged(object sender, EventArgs e)
    {
        this.SelectionStart = SelectionStart;
        this.SelectionLength = SelectionLength;
    }

    #region Text.
    /// <summary>
    /// Dependancy property for the editor text property binding.
    /// </summary>
    public static readonly DependencyProperty TextProperty =
         DependencyProperty.Register("Text", typeof(string), typeof(MvvmTextEditor),
         new PropertyMetadata((obj, args) =>
         {
             MvvmTextEditor target = (MvvmTextEditor)obj;
             target.Text = (string)args.NewValue;
         }));

    /// <summary>
    /// Provide access to the Text.
    /// </summary>
    public new string Text
    {
        get { return base.Text; }
        set { base.Text = value; }
    }

    /// <summary>
    /// Return the current text length.
    /// </summary>
    public int Length
    {
        get { return base.Text.Length; }
    }

    /// <summary>
    /// Override of OnTextChanged event.
    /// </summary>
    protected override void OnTextChanged(EventArgs e)
    {
        RaisePropertyChanged("Length");
        base.OnTextChanged(e);
    }
    #endregion // Text.

    #region Caret Offset.
    /// <summary>
    /// DependencyProperty for the TextEditorCaretOffset binding. 
    /// </summary>
    public static DependencyProperty CaretOffsetProperty =
        DependencyProperty.Register("CaretOffset", typeof(int), typeof(MvvmTextEditor),
        new PropertyMetadata((obj, args) =>
        {
            MvvmTextEditor target = (MvvmTextEditor)obj;
            target.CaretOffset = (int)args.NewValue;
        }));

    /// <summary>
    /// Provide access to the CaretOffset.
    /// </summary>
    public new int CaretOffset
    {
        get { return base.CaretOffset; }
        set { base.CaretOffset = value; }
    }
    #endregion // Caret Offset.

    #region Selection.
    /// <summary>
    /// DependencyProperty for the TextEditor SelectionLength property. 
    /// </summary>
    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;
             }));

    /// <summary>
    /// Access to the SelectionLength property.
    /// </summary>
    public new int SelectionLength
    {
        get { return base.SelectionLength; }
        set { SetValue(SelectionLengthProperty, value); }
    }

    /// <summary>
    /// DependencyProperty for the TextEditor SelectionStart property. 
    /// </summary>
    public static readonly DependencyProperty SelectionStartProperty =
         DependencyProperty.Register("SelectionStart", typeof(int), typeof(MvvmTextEditor),
         new PropertyMetadata((obj, args) =>
             {
                 MvvmTextEditor target = (MvvmTextEditor)obj;
                 target.SelectionStart = (int)args.NewValue;
             }));

    /// <summary>
    /// Access to the SelectionStart property.
    /// </summary>
    public new int SelectionStart
    {
        get { return base.SelectionStart; }
        set { SetValue(SelectionStartProperty, value); }
    }
    #endregion // Selection.

    /// <summary>
    /// Implement the INotifyPropertyChanged event handler.
    /// </summary>
    public event PropertyChangedEventHandler PropertyChanged;
    public void RaisePropertyChanged([CallerMemberName] string caller = null)
    {
        var handler = PropertyChanged;
        if (handler != null)
            PropertyChanged(this, new PropertyChangedEventArgs(caller));
    }
}

我希望这有助于其他人。

使用AvalonEdit SelectionStart，SelectionLength进行Mvvm绑定

1 个答案: