我正在尝试使用附加属性在TextBox的背景中创建一个提示文本标签,但我无法解析样式资源中文本标题的绑定:
款式定义:
<Style x:Key="CueBannerTextBoxStyle"
TargetType="TextBox">
<Style.Resources>
<VisualBrush x:Key="CueBannerBrush"
AlignmentX="Left"
AlignmentY="Center"
Stretch="None">
<VisualBrush.Visual>
<Label Content="{Binding Path=(EnhancedControls:CueBannerTextBox.Caption), RelativeSource={RelativeSource AncestorType={x:Type TextBox}}}"
Foreground="LightGray"
Background="White"
Width="200" />
</VisualBrush.Visual>
</VisualBrush>
</Style.Resources>
<Style.Triggers>
<Trigger Property="Text"
Value="{x:Static sys:String.Empty}">
<Setter Property="Background"
Value="{DynamicResource CueBannerBrush}" />
</Trigger>
<Trigger Property="Text"
Value="{x:Null}">
<Setter Property="Background"
Value="{DynamicResource CueBannerBrush}" />
</Trigger>
<Trigger Property="IsKeyboardFocused"
Value="True">
<Setter Property="Background"
Value="White" />
</Trigger>
</Style.Triggers>
</Style>
附属物:
public class CueBannerTextBox
{
public static String GetCaption(DependencyObject obj)
{
return (String)obj.GetValue(CaptionProperty);
}
public static void SetCaption(DependencyObject obj, String value)
{
obj.SetValue(CaptionProperty, value);
}
public static readonly DependencyProperty CaptionProperty =
DependencyProperty.RegisterAttached("Caption", typeof(String), typeof(CueBannerTextBox), new UIPropertyMetadata(null));
}
用法:
<TextBox x:Name="txtProductInterfaceStorageId"
EnhancedControls:CueBannerTextBox.Caption="myCustomCaption"
Width="200"
Margin="5"
Style="{StaticResource CueBannerTextBoxStyle}" />
我们的想法是,您可以在创建文本框时定义可视画笔中使用的文本提示,但我收到了绑定错误:
System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Controls.TextBox', AncestorLevel='1''. BindingExpression:Path=(0); DataItem=null; target element is 'Label' (Name=''); target property is 'Content' (type 'Object')
如果我只是硬编码样式中的Label.Content属性,代码工作正常.
有任何想法吗？
这里的问题与工作方式有关Style：基本上，将创建一个“副本” Style（在第一次引用时），此时，TextBox您可能希望将其Style应用于多个控件 - 它将用于哪个控件相对来源？
（可能的）答案是使用 aTemplate而不是 a Style- 通过控件或数据模板，您将能够访问 的可视化树TemplatedParent，这应该可以让您到达需要的位置。
编辑：进一步思考，我在这里可能是不正确的......当我回到计算机前时，我会拼凑一个快速测试工具，看看我是否可以证明/反驳这一点。
进一步编辑：虽然我最初所说的可以说是“正确的”，但这不是你的问题；劳尔所说的关于：视觉树是正确的：
Background属性设置为TextBox实例VisualBrush。Visual画笔的未映射到控件的可视化树中。{RelativeSource FindAncestor}导航都将失败，因为该视觉对象的父级将为空。Style还是 a ，情况都是如此ControlTemplate。ElementName绝对是不理想的，因为它降低了定义的可重用性。那么该怎么办？
我一夜之间绞尽脑汁试图想出一种方法来将正确的继承上下文整理到所包含的画笔中，但收效甚微……不过，我确实想出了这种超级黑客的方法：
首先，辅助属性（注意：我通常不会以这种方式设计代码，但试图节省空间）：
public class HackyMess
{
public static String GetCaption(DependencyObject obj)
{
return (String)obj.GetValue(CaptionProperty);
}
public static void SetCaption(DependencyObject obj, String value)
{
Debug.WriteLine("obj '{0}' setting caption to '{1}'", obj, value);
obj.SetValue(CaptionProperty, value);
}
public static readonly DependencyProperty CaptionProperty =
DependencyProperty.RegisterAttached("Caption", typeof(String), typeof(HackyMess),
new FrameworkPropertyMetadata(null));
public static object GetContext(DependencyObject obj) { return obj.GetValue(ContextProperty); }
public static void SetContext(DependencyObject obj, object value) { obj.SetValue(ContextProperty, value); }
public static void SetBackground(DependencyObject obj, Brush value) { obj.SetValue(BackgroundProperty, value); }
public static Brush GetBackground(DependencyObject obj) { return (Brush) obj.GetValue(BackgroundProperty); }
public static readonly DependencyProperty ContextProperty = DependencyProperty.RegisterAttached(
"Context", typeof(object), typeof(HackyMess),
new FrameworkPropertyMetadata(default(HackyMess), FrameworkPropertyMetadataOptions.OverridesInheritanceBehavior | FrameworkPropertyMetadataOptions.Inherits));
public static readonly DependencyProperty BackgroundProperty = DependencyProperty.RegisterAttached(
"Background", typeof(Brush), typeof(HackyMess),
new UIPropertyMetadata(default(Brush), OnBackgroundChanged));
private static void OnBackgroundChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
var rawValue = args.NewValue;
if (rawValue is Brush)
{
var brush = rawValue as Brush;
var previousContext = obj.GetValue(ContextProperty);
if (previousContext != null && previousContext != DependencyProperty.UnsetValue)
{
if (brush is VisualBrush)
{
// If our hosted visual is a framework element, set it's data context to our inherited one
var currentVisual = (brush as VisualBrush).GetValue(VisualBrush.VisualProperty);
if(currentVisual is FrameworkElement)
{
(currentVisual as FrameworkElement).SetValue(FrameworkElement.DataContextProperty, previousContext);
}
}
}
// Why can't there be just *one* background property? *sigh*
if (obj is TextBlock) { obj.SetValue(TextBlock.BackgroundProperty, brush); }
else if (obj is Control) { obj.SetValue(Control.BackgroundProperty, brush); }
else if (obj is Panel) { obj.SetValue(Panel.BackgroundProperty, brush); }
else if (obj is Border) { obj.SetValue(Border.BackgroundProperty, brush); }
}
}
}
现在更新了 XAML：
<Style x:Key="CueBannerTextBoxStyle"
TargetType="{x:Type TextBox}">
<Style.Triggers>
<Trigger Property="TextBox.Text"
Value="{x:Static sys:String.Empty}">
<Setter Property="local:HackyMess.Background">
<Setter.Value>
<VisualBrush AlignmentX="Left"
AlignmentY="Center"
Stretch="None">
<VisualBrush.Visual>
<Label Content="{Binding Path=(local:HackyMess.Caption)}"
Foreground="LightGray"
Background="White"
Width="200" />
</VisualBrush.Visual>
</VisualBrush>
</Setter.Value>
</Setter>
</Trigger>
<Trigger Property="IsKeyboardFocused"
Value="True">
<Setter Property="local:HackyMess.Background"
Value="White" />
</Trigger>
</Style.Triggers>
</Style>
<TextBox x:Name="txtProductInterfaceStorageId"
local:HackyMess.Caption="myCustomCaption"
local:HackyMess.Context="{Binding RelativeSource={RelativeSource Self}}"
Width="200"
Margin="5"
Style="{StaticResource CueBannerTextBoxStyle}" />
<TextBox x:Name="txtProductInterfaceStorageId2"
local:HackyMess.Caption="myCustomCaption2"
local:HackyMess.Context="{Binding RelativeSource={RelativeSource Self}}"
Width="200"
Margin="5"
Style="{StaticResource CueBannerTextBoxStyle}" />