如何绑定到文本框的 CaretIndex aka 光标位置

Question

您好，我正在尝试绑定到 TextBox.CaretIndex 属性，它不是 DependencyProperty，所以我创建了 Behavior，但它不是按预期工作。

期望（专注时）

默认值 = 0
如果我更改 view 中的值，它应该更改 viewmodel
如果我更改 viewmodel 中的值，它应该更改 view

当前行为

viewmodel 值在 window 打开时被调用

代码隐藏

public class TextBoxBehavior : DependencyObject
{
    public static readonly DependencyProperty CursorPositionProperty =
        DependencyProperty.Register(
            "CursorPosition",
            typeof(int),
            typeof(TextBoxBehavior),
            new FrameworkPropertyMetadata(
                default(int),
                new PropertyChangedCallback(CursorPositionChanged)));

    public static void SetCursorPosition(DependencyObject dependencyObject, int i)
    {
        // breakpoint get never called
        dependencyObject.SetValue(CursorPositionProperty, i); 
    }

    public static int GetCursorPosition(DependencyObject dependencyObject)
    {
        // breakpoint get never called
        return (int)dependencyObject.GetValue(CursorPositionProperty);
    }

    private static void CursorPositionChanged(
        DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
    {
        // breakpoint get never called
        //var textBox = dependencyObject as TextBox;
        //if (textBox == null) return;
    }
}

XAML

<TextBox Text="{Binding TextTemplate,UpdateSourceTrigger=PropertyChanged}"
         local:TextBoxBehavior.CursorPosition="{Binding CursorPosition}"/>

更多信息

我认为这里确实有问题，因为我需要从 DependencyObject 派生它，而以前从不需要，因为 CursorPositionProperty 已经是 DependencyProperty，所以这应该是足够的。我还认为我需要在我的 Behavior 中使用一些事件来正确设置我的 CursorPositionProperty，但我不知道是哪个。

Answer 1

正如您所说，TextBox.CaretIndex Property 是 而不是 和 DependencyProperty，因此您无法对其进行数据绑定。即使使用您自己的 DependencyProperty，它也不起作用...当 TextBox.CaretIndex 属性发生变化时，您希望如何收到通知？

Answer 2

在与我的行为作斗争之后，我可以向您展示一个 99% 可行的解决方案

行为

using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;

namespace WpfMVVMTextBoxCursorPosition
{
    public class TextBoxCursorPositionBehavior : DependencyObject
    {
        public static void SetCursorPosition(DependencyObject dependencyObject, int i)
        {
            dependencyObject.SetValue(CursorPositionProperty, i);
        }

        public static int GetCursorPosition(DependencyObject dependencyObject)
        {
            return (int)dependencyObject.GetValue(CursorPositionProperty);
        }

        public static readonly DependencyProperty CursorPositionProperty =
                                           DependencyProperty.Register("CursorPosition"
                                                                       , typeof(int)
                                                                       , typeof(TextBoxCursorPositionBehavior)
                                                                       , new FrameworkPropertyMetadata(default(int))
                                                                       {
                                                                           BindsTwoWayByDefault = true
                                                                           ,DefaultUpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged
                                                                       }
                                                                       );

        public static readonly DependencyProperty TrackCaretIndexProperty =
                                                    DependencyProperty.RegisterAttached(
                                                        "TrackCaretIndex",
                                                        typeof(bool),
                                                        typeof(TextBoxCursorPositionBehavior),
                                                        new UIPropertyMetadata(false
                                                                                , OnTrackCaretIndex));

        public static void SetTrackCaretIndex(DependencyObject dependencyObject, bool i)
        {
            dependencyObject.SetValue(TrackCaretIndexProperty, i);
        }

        public static bool GetTrackCaretIndex(DependencyObject dependencyObject)
        {
            return (bool)dependencyObject.GetValue(TrackCaretIndexProperty);
        }

        private static void OnTrackCaretIndex(DependencyObject dependency, DependencyPropertyChangedEventArgs e)
        {
            var textbox = dependency as TextBox;

            if (textbox == null)
                return;
            bool oldValue = (bool)e.OldValue;
            bool newValue = (bool)e.NewValue;

            if (!oldValue && newValue) // If changed from false to true
            {
                textbox.SelectionChanged += OnSelectionChanged;
            }
            else if (oldValue && !newValue) // If changed from true to false
            {
                textbox.SelectionChanged -= OnSelectionChanged;
            }
        }

        private static void OnSelectionChanged(object sender, RoutedEventArgs e)
        {
            var textbox = sender as TextBox;

            if (textbox != null)
                SetCursorPosition(textbox, textbox.CaretIndex); // dies line does nothing
        }
    }
}

XAML

    <TextBox Height="50" VerticalAlignment="Top"
             Name="TestTextBox"
             Text="{Binding MyText}"
             vm:TextBoxCursorPositionBehavior.TrackCaretIndex="True"
             vm:TextBoxCursorPositionBehavior.CursorPosition="{Binding CursorPosition,Mode=TwoWay}"/>

    <TextBlock Height="50" Text="{Binding CursorPosition}"/>

只是有一点我不知道为什么它不起作用 => BindsTwoWayByDefault = true。据我所知，它对绑定没有影响，因此我需要在 XAML

中显式设置绑定模式

Answer 3

我遇到了类似的问题，对我来说最简单的解决方案是继承TextBox并添加一个DependencyProperty。所以它看起来像这样：

namespace UI.Controls
{
    public class MyTextBox : TextBox
    {
        public static readonly DependencyProperty CaretPositionProperty =
            DependencyProperty.Register("CaretPosition", typeof(int), typeof(MyTextBox),
                new FrameworkPropertyMetadata(0, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, OnCaretPositionChanged));

        public int CaretPosition
        {
            get { return (int)GetValue(CaretPositionProperty); }
            set { SetValue(CaretPositionProperty, value); }
        }

        public MyTextBox()
        {
            SelectionChanged += (s, e) => CaretPosition = CaretIndex;
        }

        private static void OnCaretPositionChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            (d as MyTextBox).CaretIndex = (int)e.NewValue;
        }
    }
}

... 在我的 XAML:

xmlns:controls="clr-namespace:IU.Controls"
...
<controls:MyTextBox CaretPosition="{Binding CaretPosition}"/>

... 和 CaretPosition 属性当然在视图模型中。如果您不打算将您的视图模型绑定到其他文本编辑控件，这可能就足够了，如果是 - 您可能需要另一个解决方案。

Answer 4

WiiMaxx 的解决方案对我来说有以下问题：

当从代码更改视图模型属性时，文本框中的插入符号索引不会更改。 Tejas Vaishnav 在对解决方案的评论中也提到了这一点。
BindsTwoWayByDefault = true 无效。
他说很奇怪他需要继承DependencyObject。
TrackCaretIndex 属性仅用于初始化，感觉有点不必要。

这是我解决这些问题的方法：

行为

public static class TextBoxAssist
{

    // This strange default value is on purpose it makes the initialization problem very unlikely.
    // If the default value matches the default value of the property in the ViewModel,
    // the propertyChangedCallback of the FrameworkPropertyMetadata is initially not called
    // and if the property in the ViewModel is not changed it will never be called.
    private const int CaretIndexPropertyDefault = -485609317;

    public static void SetCaretIndex(DependencyObject dependencyObject, int i)
    {
        dependencyObject.SetValue(CaretIndexProperty, i);
    }

    public static int GetCaretIndex(DependencyObject dependencyObject)
    {
        return (int)dependencyObject.GetValue(CaretIndexProperty);
    }

    public static readonly DependencyProperty CaretIndexProperty =
        DependencyProperty.RegisterAttached(
            "CaretIndex",
            typeof(int),
            typeof(TextBoxAssist),
            new FrameworkPropertyMetadata(
                CaretIndexPropertyDefault,
                FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
                CaretIndexChanged));

    private static void CaretIndexChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs eventArgs)
    {
        if (dependencyObject is not TextBox textBox || eventArgs.OldValue is not int oldValue || eventArgs.NewValue is not int newValue)
        {
            return;
        }

        if (oldValue == CaretIndexPropertyDefault && newValue != CaretIndexPropertyDefault)
        {
            textBox.SelectionChanged += SelectionChangedForCaretIndex;
        }
        else if (oldValue != CaretIndexPropertyDefault && newValue == CaretIndexPropertyDefault)
        {
            textBox.SelectionChanged -= SelectionChangedForCaretIndex;
        }

        if (newValue != textBox.CaretIndex)
        {
            textBox.CaretIndex = newValue;
        }
    }

    private static void SelectionChangedForCaretIndex(object sender, RoutedEventArgs eventArgs)
    {
        if (sender is TextBox textBox)
        {
            SetCaretIndex(textBox, textBox.CaretIndex);
        }
    }

}

XAML

    <TextBox Height="50" VerticalAlignment="Top"
             Name="TestTextBox"
             Text="{Binding MyText}"
             viewModels:TextBoxAssist.CaretIndex="{Binding CaretIndex}"/>

对差异的一些说明：

视图模型属性更改现在有效，因为 TextBox 上的插入符号索引设置在 CaretIndexChanged 的末尾。
BindsTwoWayByDefault 已通过使用相应的 FrameworkPropertyMetadata 构造函数参数修复。
仅需要从 DependencyObject 继承，因为使用 DependencyProperty.Register 而不是 DependencyProperty.RegisterAttached。
没有 TrackCaretIndex 属性我遇到的问题是 FrameworkPropertyMetadata 的 propertyChangedCallback 从未被调用来正确初始化。仅当 FrameworkPropertyMetadata 的默认值从一开始就与视图模型属性的值匹配并且视图模型属性未更改时才会出现此问题。这就是我使用这个随机默认值的原因。

如何绑定到文本框的 CaretIndex aka 光标位置

How to Bind to CaretIndex aka curser position of an Textbox

c#

wpf

binding

textbox

mvvm