Question

我发现了这个问题MVVM and the TextBox's SelectedText property。但是，我无法获得解决方案。这是我的非工作代码，我试图在第二个文本框中显示第一个文本框的选定文本。

查看：

SelectedText和Text只是我的ViewModel的字符串属性。

<TextBox Text="{Binding Path=Text, UpdateSourceTrigger=PropertyChanged}"  Height="155" HorizontalAlignment="Left" Margin="68,31,0,0" Name="textBox1" VerticalAlignment="Top" Width="264" AcceptsReturn="True" AcceptsTab="True" local:TextBoxHelper.SelectedText="{Binding SelectedText, UpdateSourceTrigger=PropertyChanged, Mode=OneWayToSource}" />
        <TextBox Text="{Binding SelectedText, Mode=OneWay, UpdateSourceTrigger=PropertyChanged}" Height="154" HorizontalAlignment="Left" Margin="82,287,0,0" Name="textBox2" VerticalAlignment="Top" Width="239" />

TextBoxHelper

 public static class TextBoxHelper
{
    #region "Selected Text"
    public static string GetSelectedText(DependencyObject obj)
    {
        return (string)obj.GetValue(SelectedTextProperty);
    }

    public static void SetSelectedText(DependencyObject obj, string value)
    {
        obj.SetValue(SelectedTextProperty, value);
    }

    // Using a DependencyProperty as the backing store for SelectedText.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty SelectedTextProperty =
        DependencyProperty.RegisterAttached(
            "SelectedText",
            typeof(string),
            typeof(TextBoxHelper),
            new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, SelectedTextChanged));

    private static void SelectedTextChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
    {
        TextBox tb = obj as TextBox;
        if (tb != null)
        {
            if (e.OldValue == null && e.NewValue != null)
            {
                tb.SelectionChanged += tb_SelectionChanged;
            }
            else if (e.OldValue != null && e.NewValue == null)
            {
                tb.SelectionChanged -= tb_SelectionChanged;
            }

            string newValue = e.NewValue as string;

            if (newValue != null && newValue != tb.SelectedText)
            {
                tb.SelectedText = newValue as string;
            }
        }
    }

    static void tb_SelectionChanged(object sender, RoutedEventArgs e)
    {
        TextBox tb = sender as TextBox;
        if (tb != null)
        {
            SetSelectedText(tb, tb.SelectedText);
        }
    }
    #endregion

}

我做错了什么？

Answer 1

为了使SelectedTextChanged处理程序触发SelectedText属性必须具有初始值。如果你没有将它初始化为某个值（string.Empty作为最低限度），那么这个处理程序永远不会触发，反过来你永远不会注册tb_SelectionChanged处理程序。

Answer 2

这不起作用的原因是没有引发属性更改回调（因为VM的绑定值与属性的元数据中指定的默认值相同）。但更重要的是，当所选文本设置为null时，您的行为将分离。在这种情况下，我倾向于使用另一个附加属性，该属性仅用于启用对所选文本的监视，然后可以绑定SelectedText属性。所以，像这样：

#region IsSelectionMonitored
public static readonly DependencyProperty IsSelectionMonitoredProperty = DependencyProperty.RegisterAttached(
    "IsSelectionMonitored",
    typeof(bool),
    typeof(PinnedInstrumentsViewModel),
    new FrameworkPropertyMetadata(OnIsSelectionMonitoredChanged));

[AttachedPropertyBrowsableForType(typeof(TextBox))]
public static bool GetIsSelectionMonitored(TextBox d)
{
    return (bool)d.GetValue(IsSelectionMonitoredProperty);
}

public static void SetIsSelectionMonitored(TextBox d, bool value)
{
    d.SetValue(IsSelectionMonitoredProperty, value);
}

private static void OnIsSelectionMonitoredChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
    TextBox tb = obj as TextBox;
    if (tb != null)
    {
        if ((bool)e.NewValue)
        {
            tb.SelectionChanged += tb_SelectionChanged;
        }
        else
        {
            tb.SelectionChanged -= tb_SelectionChanged;
        }

        SetSelectedText(tb, tb.SelectedText);
    }
}
#endregion

#region "Selected Text"
public static string GetSelectedText(DependencyObject obj)
{
    return (string)obj.GetValue(SelectedTextProperty);
}

public static void SetSelectedText(DependencyObject obj, string value)
{
    obj.SetValue(SelectedTextProperty, value);
}

// Using a DependencyProperty as the backing store for SelectedText.  This enables animation, styling, binding, etc...
public static readonly DependencyProperty SelectedTextProperty =
    DependencyProperty.RegisterAttached(
        "SelectedText",
        typeof(string),
        typeof(TextBoxHelper),
        new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, SelectedTextChanged));

private static void SelectedTextChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
    TextBox tb = obj as TextBox;
    if (tb != null)
    {
        tb.SelectedText = e.NewValue as string;            
    }
}

static void tb_SelectionChanged(object sender, RoutedEventArgs e)
{
    TextBox tb = sender as TextBox;
    if (tb != null)
    {
        SetSelectedText(tb, tb.SelectedText);
    }
}
#endregion

然后在你的XAML中，你必须将该属性添加到你的第一个TextBox：

<TextBox ... local:TextBoxHelper.IsSelectionMonitored="True" local:TextBoxHelper.SelectedText="{Binding SelectedText, Mode=OneWayToSource}" />

Answer 3

这适用于我使用TextBoxHelper类。如前所述，您需要使用非null值初始化TextBoxHelper的SelectedText属性。您应该绑定到应该实现INotifyPropertyChanged的VM的字符串属性，而不是数据绑定到视图上的字符串属性（SelText）。

XAML：

<Window x:Class="TextSelectDemo.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:TextSelectDemo"
    Height="300" Width="300">
    <StackPanel>
        <TextBox local:TextBoxHelper.SelectedText="{Binding Path=SelText, Mode=TwoWay}" />
        <TextBox Text="{Binding Path=SelText}" />
    </StackPanel>
</Window>

代码背后：

using System.ComponentModel;
using System.Windows;

namespace TextSelectDemo
{
    public partial class Window1 : Window, INotifyPropertyChanged
    {
        public Window1()
        {
            InitializeComponent();

            SelText = string.Empty;

            DataContext = this;
        }

        private string _selText;
        public string SelText
        {
            get { return _selText; }
            set
            {
                _selText = value;
                if (PropertyChanged != null)
                {
                    PropertyChanged(this, new PropertyChangedEventArgs("SelText"));
                }
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
    }
}

Answer 4

您的绑定尝试将Text的{{1}}属性绑定到TextBox的当前数据上下文的SelectedText属性。由于您正在使用附加属性，而不是使用数据上下文中的属性，因此您需要在绑定中提供更多信息：

TextBox

<TextBox Text="{Binding local:TextBoxHelper.SelectedText, Mode=OneWay, UpdateSourceTrigger=PropertyChanged}" ... />与包含local类的CLR命名空间关联的位置。

Answer 5

您需要一个普通的.net属性包装器，用于dependencyproperty，有些像：

public string SelectedText
{
   set {SetSelectedText(this, value);}
...

运行时不需要它（运行时使用set / get），但设计者和编译器需要它。

MVVM-如何绑定到属性，而不是依赖属性？

5 个答案: