MVVM 和 TextBox 的 SelectedText 属性 [英] MVVM and the TextBox's SelectedText property

问题描述

我有一个带有 ContextMenu 的 TextBox.当用户在 TextBox 内右键单击并选择适当的 MenuItem 时，我想在我的视图模型中获取 SelectedText.我还没有找到一个很好的方法来做到这一点MVVM"的方式.

I have a TextBox with a ContextMenu in it. When the user right clicks inside the TextBox and chooses the appropriate MenuItem, I would like to grab the SelectedText in my viewmodel. I have not found a good way to do this the "MVVM" way.

到目前为止，我的应用程序使用了 Josh Smith 的 MVVM 方式.我正在寻找转移到 Cinch.不确定 Cinch 框架是否会处理这样的问题.想法?

So far I have my appliction utilizing Josh Smith's way of MVVM. I am looking to tranfer over to Cinch. Not sure if the Cinch framework will handle issues like this. Thoughts?

推荐答案

没有直接的方法可以将 SelectedText 绑定到数据源，因为它不是 DependencyProperty...但是，创建附加属性非常容易，您可以改为绑定.

There's no straightforward way to bind SelectedText to a data source, because it's not a DependencyProperty... however, it quite easy to create an attached property that you could bind instead.

这是一个基本的实现:

public static class TextBoxHelper
{

    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);
        }
    }

}

然后您可以像在 XAML 中那样使用它:

You can then use it like that in XAML :

<TextBox Text="{Binding Message}" u:TextBoxHelper.SelectedText="{Binding SelectedText}" />

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