数据绑定 TextBlock 在 Silverlight/WP7 中运行 [英] Databinding TextBlock Runs in Silverlight / WP7

问题描述

我在 Windows Phone 7 上使用 Silverlight.

I'm using Silverlight on Windows Phone 7.

我想以粗体显示 TextBlock 中某些文本的第一部分，其余部分以普通字体显示.完整的文本必须换行.我希望粗体部分包含来自我的 ViewModel 中一个属性的文本，而纯文本包含来自不同属性的文本.

I want to display the first part of some text in a TextBlock in bold, and the rest in normal font. The complete text must wrap. I want the bolded part to contain text from one property in my ViewModel, and the plain text to contain text from a different property.

TextBlock 在与 LongListSelector 关联的 DataTemplate 中定义.

The TextBlock is defined in a DataTemplate associated with a LongListSelector.

我最初的尝试是:

<TextBlock TextWrapping="Wrap">
  <TextBlock.Inlines>
    <Run Text="{Binding Property1}" FontWeight="Bold"/>
    <Run Text="{Binding Property2}"/>
  </TextBlock.Inlines>
</TextBlock>

这在运行时失败，并显示非常无用的AG_E_RUNTIME_MANAGED_UNKNOWN_ERROR".这是一个已知问题，因为 Run 元素不是 FrameworkElement 并且无法绑定.

This fails at runtime with the spectacularly unhelpful "AG_E_RUNTIME_MANAGED_UNKNOWN_ERROR". This is a known issue because the Run element is not a FrameworkElement and cannot be bound.

我的下一个尝试是放置占位符，然后在代码中更新它们:

My next attempt was to put placeholders in place, and then update them in code:

<TextBlock Loaded="TextBlockLoaded" TextWrapping="Wrap">
    <TextBlock.Inlines>
        <Run FontWeight="Bold">Placeholder1</Run>
        <Run>Placeholder2</Run>
    </TextBlock.Inlines>
</TextBlock>

在代码隐藏中(是的，我很绝望！):

In the code-behind (yes I am desparate!):

private void TextBlockLoaded(object sender, RoutedEventArgs e)
{
    var textBlock = (TextBlock)sender;
    var viewModel = (ViewModel)textBlock.DataContext;
    var prop1Run = (Run)textBlock.Inlines[0];
    var prop2Run = (Run)textBlock.Inlines[1];
    prop1Run.Text = viewModel.Property1;
    prop2Run.Text = viewModel.Property2;
}

这似乎有效，但因为我使用的是 LongListSelector，虽然项目被回收，但 Loaded 代码隐藏事件处理程序不会重新初始化运行，所以很快就会显示错误的文本...

This seemed to work, but because I am using the LongListSelector, although items get recycled, the Loaded codebehind event handler doesn't re-initialize the Runs, so very quickly the wrong text is displayed...

我已经研究过使用 LongListSelector 的 Linked 事件(我已经用它来释放我在列表中显示的图像)，但我看不到如何使用它来重新初始化 Runs 的文本属性.

I've looked at using the LongListSelector's Linked event (which I already use to free up images that I display in the list), but I can't see how I can use that to re-initialize the Runs' text properties.

感谢任何帮助！

推荐答案

我终于找到了适合我的解决方案.

I finally found a solution that works for me.

正如我在评论中提到的，Paul Stovell 的方法不工作.

As I mention in the comment, Paul Stovell's approach would not work.

相反，我使用类似的方法将附加属性添加到 TextBlock，绑定到 TextBlock 的 DataContext，并在运行时附加属性，指示它们应该绑定到哪些 ViewModel 属性:

Instead I used a similar approach to add an attached property to the TextBlock, bound to the TextBlock's DataContext, and attached properties on the runs, indicating which ViewModel properties they should be bound to:

<TextBlock TextWrapping="Wrap"
            Views:BindableRuns.Target="{Binding}">
    <TextBlock.Inlines>
        <Run FontWeight="Bold" Views:BindableRuns.Target="Property1"/>
        <Run Views:BindableRuns.Target="Property2"/>
    </TextBlock.Inlines>
</TextBlock>

然后在我附加的 TextBox Target (datacontext) 属性的更改事件中，我更新了 Runs，并订阅了 TextBox Target 属性更改的通知.当 TextBox Target 属性发生变化时，我会相应地更新任何关联的 Run 文本.

Then in my attached TextBox Target (datacontext) property's changed event, I update the Runs, and subscribe to be notified of changes to the TextBox Target properties. When a TextBox Target property changes, I updated any associated Run's text accordingly.

public static class BindableRuns
{
    private static readonly Dictionary<INotifyPropertyChanged, PropertyChangedHandler> 
        Handlers = new Dictionary<INotifyPropertyChanged, PropertyChangedHandler>();

    private static void TargetPropertyPropertyChanged(
                                    DependencyObject dependencyObject,
                                    DependencyPropertyChangedEventArgs e)
    {
        if(!(dependencyObject is TextBlock)) return;

        var textBlock = (TextBlock)dependencyObject;
        AddHandler(e.NewValue as INotifyPropertyChanged, textBlock);
        RemoveHandler(e.OldValue as INotifyPropertyChanged);
        InitializeRuns(textBlock, e.NewValue);
    }

    private static void AddHandler(INotifyPropertyChanged dataContext,
                                   TextBlock textBlock)
    {
        if (dataContext == null) return;

        var propertyChangedHandler = new PropertyChangedHandler(textBlock);
        dataContext.PropertyChanged += propertyChangedHandler.PropertyChanged;
        Handlers[dataContext] = propertyChangedHandler;
    }

    private static void RemoveHandler(INotifyPropertyChanged dataContext)
    {
        if (dataContext == null || !Handlers.ContainsKey(dataContext)) return;

        dataContext.PropertyChanged -= Handlers[dataContext].PropertyChanged;
        Handlers.Remove(dataContext);
    }

    private static void InitializeRuns(TextBlock textBlock, object dataContext)
    {
        if (dataContext == null) return;

        var runs = from run in textBlock.Inlines.OfType<Run>()
                   let propertyName = (string)run.GetValue(TargetProperty)
                   where propertyName != null
                   select new { Run = run, PropertyName = propertyName };


        foreach (var run in runs)
        {
            var property = dataContext.GetType().GetProperty(run.PropertyName);
            run.Run.Text = (string)property.GetValue(dataContext, null);
        }
    }

    private class PropertyChangedHandler
    {
        private readonly TextBlock _textBlock;
        public PropertyChangedHandler(TextBlock textBlock)
        {
            _textBlock = textBlock;
        }

        public void PropertyChanged(object sender,
                                    PropertyChangedEventArgs propertyChangedArgs)
        {
            var propertyName = propertyChangedArgs.PropertyName;
            var run = _textBlock.Inlines.OfType<Run>()
                .Where(r => (string) r.GetValue(TargetProperty) == propertyName)
                .SingleOrDefault();
            if(run == null) return;

            var property = sender.GetType().GetProperty(propertyName);
            run.Text = (string)property.GetValue(sender, null);
        }

    }


    public static object GetTarget(DependencyObject obj)
    {
        return obj.GetValue(TargetProperty);
    }

    public static void SetTarget(DependencyObject obj,
        object value)
    {
        obj.SetValue(TargetProperty, value);
    }

    public static readonly DependencyProperty TargetProperty =
        DependencyProperty.RegisterAttached("Target",
            typeof(object),
            typeof(BindableRuns),
            new PropertyMetadata(null,
                TargetPropertyPropertyChanged));

}

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