Question

在Silverlight 3.0应用程序中，我试图在画布中创建一个矩形，并使其拉伸画布的整个宽度。我试图通过绑定到父容器的ActualWidth属性（下面的示例）来做到这一点，但是当我没有看到任何绑定错误时，该值没有被绑定。矩形不可见，因为其宽度为零。另外尝试绑定到包含我的矩形的画布的ActualWidth，但这没有区别。

我做了find this bug logged on Microsoft Connect，但没有列出变通办法。

有没有人能够解决这个问题，还是他们能指出解决方案？

编辑：原始代码示例不准确，我想要实现的目标，更新更清晰。

<UserControl>
    <Border BorderBrush="White"
            BorderThickness="1"
            CornerRadius="4"
            HorizontalAlignment="Center">
        <Grid x:Name="GridContainer">
            <Rectangle Fill="Aqua"
                       Width="150"
                       Height="400" />
            <Canvas>
                <Rectangle Width="{Binding Path=ActualWidth, ElementName=GridContainer}"
                           Height="30"
                           Fill="Red" />
            </Canvas>

            <StackPanel>
                <!-- other elements here -->
            </StackPanel>
        </Grid>
    </Border>
</UserControl>

Answer 1

你想要做什么，需要你数据绑定到ActualWidth属性？这是Silverlight的一个已知问题，并没有简单的解决方法。

可以做的一件事是以这样的方式设置可视化树，即您不需要实际设置矩形的宽度，只需允许它拉伸到适当的大小。因此，在上面的示例中，如果您删除Canvas（或将Canvas更改为其他Panel）并将Rectangle的{{1}}设置为HorizontalAlignment，则会占用所有可用的宽度（实际上是网格的宽度）。

但是，在您的特定情况下可能无法实现，并且可能确实需要设置数据绑定。已经确定这是不可能的直接，但在代理对象的帮助下，我们可以设置所需的绑定。请考虑以下代码：

Stretch

我们可以在xaml中使用它，如下所示：

public class ActualSizePropertyProxy : FrameworkElement, INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public FrameworkElement Element
    {
        get { return (FrameworkElement)GetValue(ElementProperty); }
        set { SetValue(ElementProperty, value); }
    }

    public double ActualHeightValue
    {
        get{ return Element == null? 0: Element.ActualHeight; }
    }

    public double ActualWidthValue
    {
        get { return Element == null ? 0 : Element.ActualWidth; }
    }

    public static readonly DependencyProperty ElementProperty =
        DependencyProperty.Register("Element", typeof(FrameworkElement), typeof(ActualSizePropertyProxy), 
                                    new PropertyMetadata(null,OnElementPropertyChanged));

    private static void OnElementPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        ((ActualSizePropertyProxy)d).OnElementChanged(e);
    }

    private void OnElementChanged(DependencyPropertyChangedEventArgs e)
    {
        FrameworkElement oldElement = (FrameworkElement)e.OldValue;
        FrameworkElement newElement = (FrameworkElement)e.NewValue;

        newElement.SizeChanged += new SizeChangedEventHandler(Element_SizeChanged);
        if (oldElement != null)
        {
            oldElement.SizeChanged -= new SizeChangedEventHandler(Element_SizeChanged);
        }
        NotifyPropChange();
    }

    private void Element_SizeChanged(object sender, SizeChangedEventArgs e)
    {
        NotifyPropChange();
    }

    private void NotifyPropChange()
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs("ActualWidthValue"));
            PropertyChanged(this, new PropertyChangedEventArgs("ActualHeightValue"));
        }
    }
}

因此我们将TextBlock.Text绑定到代理对象上的ActualWidthValue。代理对象依次提供Element的ActualWidth，它由另一个Binding提供。

这不是解决问题的简单方法，但我能想到如何将数据绑定到ActualWidth是最好的。

如果您更多地解释了您的情景，可能会提出一个更简单的解决方案。根本不需要DataBinding;是否可以从SizeChanged事件处理程序中的代码设置属性？

Answer 2

使用附加属性的机制，可以定义代表ActualHeight和ActualWidth并由SizeChanged事件更新的属性。它的用法如下所示。

<Grid local:SizeChange.IsEnabled="True" x:Name="grid1">...</Grid>

<TextBlock Text="{Binding ElementName=grid1,
                         Path=(local:SizeChange.ActualHeight)}"/>

技术细节可在以下网址找到：

http://darutk-oboegaki.blogspot.com/2011/07/binding-actualheight-and-actualwidth.html

此解决方案与其他解决方案相比的优势在于，解决方案中定义的附加属性（SizeChange.ActualHeight和SizeChange.ActualWidth）可用于任何FrameworkElement，而无需创建任何子类。 此解决方案可重复使用且侵入性较小。

如果链接变得陈旧，这里是SizeChange Class，如链接所示：

// Declare SizeChange class as a sub class of DependencyObject

// because we need to register attached properties.
public class SizeChange : DependencyObject
 {
     #region Attached property "IsEnabled"

    // The name of IsEnabled property.
    public const string IsEnabledPropertyName = "IsEnabled";

    // Register an attached property named "IsEnabled".
    // Note that OnIsEnabledChanged method is called when
    // the value of IsEnabled property is changed.
    public static readonly DependencyProperty IsEnabledProperty
         = DependencyProperty.RegisterAttached(
             IsEnabledPropertyName,
             typeof(bool),
             typeof(SizeChange),
             new PropertyMetadata(false, OnIsEnabledChanged));

    // Getter of IsEnabled property. The name of this method
    // should not be changed because the dependency system
    // uses it.
    public static bool GetIsEnabled(DependencyObject obj)
     {
         return (bool)obj.GetValue(IsEnabledProperty);
     }

    // Setter of IsEnabled property. The name of this method
    // should not be changed because the dependency system
    // uses it.
    public static void SetIsEnabled(DependencyObject obj, bool value)
     {
         obj.SetValue(IsEnabledProperty, value);
     }

     #endregion

     #region Attached property "ActualHeight"

    // The name of ActualHeight property.
    public const string ActualHeightPropertyName = "ActualHeight";

    // Register an attached property named "ActualHeight".
    // The value of this property is updated When SizeChanged
    // event is raised.
    public static readonly DependencyProperty ActualHeightProperty
         = DependencyProperty.RegisterAttached(
             ActualHeightPropertyName,
             typeof(double),
             typeof(SizeChange),
             null);

    // Getter of ActualHeight property. The name of this method
    // should not be changed because the dependency system
    // uses it.
    public static double GetActualHeight(DependencyObject obj)
     {
         return (double)obj.GetValue(ActualHeightProperty);
     }

    // Setter of ActualHeight property. The name of this method
    // should not be changed because the dependency system
    // uses it.
    public static void SetActualHeight(DependencyObject obj, double value)
     {
         obj.SetValue(ActualHeightProperty, value);
     }

     #endregion

     #region Attached property "ActualWidth"

    // The name of ActualWidth property.
    public const string ActualWidthPropertyName = "ActualWidth";

    // Register an attached property named "ActualWidth".
    // The value of this property is updated When SizeChanged
    // event is raised.
    public static readonly DependencyProperty ActualWidthProperty
         = DependencyProperty.RegisterAttached(
             ActualWidthPropertyName,
             typeof(double),
             typeof(SizeChange),
             null);

    // Getter of ActualWidth property. The name of this method
    // should not be changed because the dependency system
    // uses it.
    public static double GetActualWidth(DependencyObject obj)
     {
         return (double)obj.GetValue(ActualWidthProperty);
     }

    // Setter of ActualWidth property. The name of this method
    // should not be changed because the dependency system
    // uses it.
    public static void SetActualWidth(DependencyObject obj, double value)
     {
         obj.SetValue(ActualWidthProperty, value);
     }

     #endregion

    // This method is called when the value of IsEnabled property
    // is changed. If the new value is true, an event handler is
    // added to SizeChanged event of the target element.
    private static void OnIsEnabledChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
     {
        // The given object must be a FrameworkElement instance,
        // because we add an event handler to SizeChanged event
        // of it.
        var element = obj as FrameworkElement;

         if (element == null)
         {
            // The given object is not an instance of FrameworkElement,
            // meaning SizeChanged event is not available. So, nothing
            // can be done for the object.
            return;
         }

        // If IsEnabled=True
        if (args.NewValue != null && (bool)args.NewValue == true)
         {
             // Attach to the element.
             Attach(element);
         }
         else
         {
             // Detach from the element.
             Detach(element);
         }
     }

     private static void Attach(FrameworkElement element)
     {
        // Add an event handler to SizeChanged event of the element

        // to take action when actual size of the element changes.
        element.SizeChanged += HandleSizeChanged;
     }

     private static void Detach(FrameworkElement element)
     {
        // Remove the event handler from the element.
        element.SizeChanged -= HandleSizeChanged;
     }

    // An event handler invoked when SizeChanged event is raised.
    private static void HandleSizeChanged(object sender, SizeChangedEventArgs args)
     {
         var element = sender as FrameworkElement;

         if (element == null)
         {
             return;
         }

        // Get the new actual height and width.
        var width  = args.NewSize.Width;
         var height = args.NewSize.Height;

        // Update values of SizeChange.ActualHeight and

        // SizeChange.ActualWidth.
        SetActualWidth(element, width);
         SetActualHeight(element, height);
     }
 }

Answer 3

我知道的方式太晚了，但只是在努力解决这个问题。我的解决方案是声明我自己的DependencyProperty名为RealWidth并更新其SizeChanged事件的值。然后，您可以绑定到RealWidth，它将更新，与ActualWidth属性不同。

public MyControl()
{
    InitializeComponent();
    SizeChanged += HandleSizeChanged;
}

public static DependencyProperty RealWidthProperty =
     DependencyProperty.Register("RealWidth", typeof (double),
     typeof (MyControl),
     new PropertyMetadata(500D));

public double RealWidth
{
    get { return (double) GetValue(RealWidthProperty); }
    set { SetValue(RealWidthProperty, value); }
}

private void HandleSizeChanged(object sender, SizeChangedEventArgs e)
{
    RealWidth = e.NewSize.Width;
}

Answer 4

为什么不创建一个继承自ContentPresenter且实际上可以提供当前大小的简单面板控件。

public class SizeNotifyPanel : ContentPresenter
{
    public static DependencyProperty SizeProperty =
        DependencyProperty.Register("Size",
                                    typeof (Size),
                                    typeof (SizeNotifyPanel),
                                    null);

    public Size Size
    {
        get { return (Size) GetValue(SizeProperty); }
        set { SetValue(SizeProperty, value); }
    }

    public SizeNotifyPanel()
    {
        SizeChanged += (s, e) => Size = e.NewSize;
    }
}

然后应将其用作实际内容的包装。

<local:SizeNotifyPanel x:Name="Content">
    <TextBlock Text="{Binding Size.Height, ElementName=Content}" />
</local:SizeNotifyPanel>

为我工作就像一个魅力，看起来很干净。

Answer 5

基于@ darutk的answer，这是一个附属的基于属性的解决方案，可以非常优雅地完成工作。

public static class SizeBindings
{
    public static readonly DependencyProperty ActualHeightProperty =
        DependencyProperty.RegisterAttached("ActualHeight", typeof (double), typeof (SizeBindings),
                                            new PropertyMetadata(0.0));

    public static readonly DependencyProperty ActualWidthProperty =
        DependencyProperty.RegisterAttached("ActualWidth", typeof (Double), typeof (SizeBindings),
                                            new PropertyMetadata(0.0));

    public static readonly DependencyProperty IsEnabledProperty =
        DependencyProperty.RegisterAttached("IsEnabled", typeof (bool), typeof (SizeBindings),
                                            new PropertyMetadata(false, HandlePropertyChanged));

    private static void HandlePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var element = d as FrameworkElement;
        if (element == null)
        {
            return;
        }

        if ((bool) e.NewValue == false)
        {
            element.SizeChanged -= HandleSizeChanged;
        }
        else
        {
            element.SizeChanged += HandleSizeChanged;
        }
    }

    private static void HandleSizeChanged(object sender, SizeChangedEventArgs e)
    {
        var element = sender as FrameworkElement;

        SetActualHeight(element, e.NewSize.Height);
        SetActualWidth(element, e.NewSize.Width);
    }

    public static bool GetIsEnabled(DependencyObject obj)
    {
        return (bool)obj.GetValue(IsEnabledProperty);
    }

    public static void SetIsEnabled(DependencyObject obj, bool value)
    {
        obj.SetValue(IsEnabledProperty, value);
    }

    public static Double GetActualWidth(DependencyObject obj)
    {
        return (Double) obj.GetValue(ActualWidthProperty);
    }

    public static void SetActualWidth(DependencyObject obj, Double value)
    {
        obj.SetValue(ActualWidthProperty, value);
    }

    public static double GetActualHeight(DependencyObject obj)
    {
        return (double)obj.GetValue(ActualHeightProperty);
    }

    public static void SetActualHeight(DependencyObject obj, double value)
    {
        obj.SetValue(ActualHeightProperty, value);
    }
}

像这样使用：

    <Grid>
        <Border x:Name="Border" behaviors:SizeBindings.IsEnabled="True"/>
        <Border MinWidth="{Binding (behaviors:SizeBindings.ActualWidth), ElementName=Border}"/>
    </Grid>

Answer 6

我已经测试了您使用TestConverter发布的更新的xaml，以查看传递给宽度的值，它对我有用（我使用的是VS 2010 B2）。要使用TestConverter，只需在Convert方法中设置断点即可。

    public class TestConverter : IValueConverter
    {

        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            return value;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            return value;
        }

    }

传入的值为150，矩形的宽度为150.

你期待不同的东西吗？

Answer 7

这是一个作为旁白的答案，可以帮助某人绑定ActualWidth。

我的进程不需要更改事件，它需要一个当前状态值的结果。所以我在自定义控件/进程上创建了一个名为Target的依赖项属性FrameworkElement，并且使用者xaml将绑定到相关的实际对象。

当计算时间时，代码可以拉出实际对象并从中提取ActualWidth。

控制中的依赖属性

public FrameworkElement Target
{
    get { return (FrameworkElement)GetValue(TargetProperty);}
    set { SetValue(TargetProperty, value);}
}

// Using a DependencyProperty as the backing store for Target.
// This enables animation, styling, binding, general access etc...
public static readonly DependencyProperty TargetProperty =
    DependencyProperty.Register("Target", typeof(FrameworkElement), 
                                typeof(ThicknessWrapper), 
                                new PropertyMetadata(null, OnTargetChanged));

消费者方面的XAML显示绑定到矩形

<local:ThicknessWrapper Target="{Binding ElementName=thePanel}"/>

<Rectangle x:Name="thePanel" HorizontalAlignment="Stretch" Height="20"  Fill="Blue"/>

获取代码

double width;

if (Target != null)
   width = Target.ActualWidth;  // Gets the current value.

Answer 8

根据KeithMahoney的答案，它在我的UWP应用程序上工作正常并解决了我的问题。但是，我无法在设计时看到我的控件，因为在设计时没有提供 ActualWidthValue 和 ActualHeightValue 的初始值。虽然它在运行时工作正常，但是设计我的控件的布局是不方便的。稍加修改，就可以解决这个问题。

在 ActualWidthValue 和 ActualHeightValue 属性的c＃代码中，添加

设置{;}

让我们可以从XAML代码中提供虚拟值。虽然它对运行时间没用，但它可以用于设计时间。
在他的XAML代码的资源声明中，为 ActualWidthValue 和 ActualHeightValue提供 c：ActualSizePropertyProxy 合适的值，例如

ActualHeightValue =＆＃34; 800＆＃34; ActualWidthValue =＆＃34; 400＆＃34;

然后它会在设计时显示400x800控件。

绑定到ActualWidth不起作用

8 个答案: