MVVM和TextBox的SelectedText属性

Question

我有一个带有ContextMenu的TextBox.当用户右键单击TextBox并选择适当的MenuItem时,我想在我的viewmodel中获取SelectedText.我还没有找到一种很好的方法来实现"MVVM"方式.

到目前为止,我的应用程序利用了Josh Smith的MVVM方式.我期待转移到Cinch.不确定Cinch框架是否会处理这样的问题.思考？

Answer 1

将SelectedText绑定到数据源没有直接的方法,因为它不是DependencyProperty ...但是,创建一个可以绑定的附加属性非常容易.

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:

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