自定义控件动态更新文本属性

Question

我有一个基于按钮的自定义控件，可以包含如下文本：

public class TextButtonControl : Button
{
    public bool AllCaps
    {
        get => (bool)GetValue(AllCapsProperty);
        set => SetValue(AllCapsProperty, value);
    }
    public static readonly DependencyProperty AllCapsProperty =
        DependencyProperty.Register("AllCaps", typeof(bool), typeof(TextButtonControl), new PropertyMetadata(false));

    public string Text
    {
        get => (string)GetValue(TextProperty);
        set => SetValue(TextProperty, value);
    }
    public static readonly DependencyProperty TextProperty =
        DependencyProperty.Register("Text", typeof(string), typeof(TextButtonControl), new PropertyMetadata(""));

    static TextButtonControl()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(TextButtonControl), new FrameworkPropertyMetadata(typeof(TextButtonControl)));
    }
}

<ControlTemplate TargetType="{x:Type local:TextButtonControl}">
    <Border Width="{TemplateBinding Width}" Height="{TemplateBinding Height}" BorderBrush="Red" BorderThickness="2">
        <TextBlock Text="{TemplateBinding Text}"
                   FontFamily="{TemplateBinding FontFamily}"
                   FontSize="{TemplateBinding FontSize}"
                   VerticalAlignment="Center"
                   HorizontalAlignment="Center"
                   TextAlignment="Center"/>
    </Border>
</ControlTemplate>

当依赖属性 AllCaps 更新时，如何使控件的文本从大写变为小写（反之亦然）？

示例用法：

<!-- inside some window or user control -->
<ToggleButton x:Name="tbCaseToggle" />
<custom:TextButtonControl Text="some text" Capitalised="{Binding ElementName=tbCaseToggle, Path=IsChecked}" />

在切换按钮被选中或取消选中时更改按钮内容的大小写。

Answer 1

多值转换器

您可以为此创建一个多转换器，它需要一个布尔值来指示大写和文本。

public class CapitalizationConverter : IMultiValueConverter
{
   public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
   {
      var capitalize = (bool)values[0];
      var text = (string)values[1];

      // Change the capitalization here as you need
      return capitalize ? text.ToUpper() : text.ToLower();
   }

   public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
   {
      throw new InvalidOperationException();
   }
}

在您的控件模板可以访问的资源字典中创建转换器的实例。

<local:CapitalizationConverter x:Key="CapitalizationConverter"/>

然后在控件模板中使用多重绑定，绑定AllCaps 和Text 属性，并根据AllCaps 的值使用转换器将文本大写。

<ControlTemplate x:Key="TextButtonControlTemplate" TargetType="{x:Type local:TextButtonControl}">
   <Border Width="{TemplateBinding Width}" Height="{TemplateBinding Height}" BorderBrush="Red" BorderThickness="2">
      <TextBlock FontFamily="{TemplateBinding FontFamily}"
                 FontSize="{TemplateBinding FontSize}"
                 VerticalAlignment="Center"
                 HorizontalAlignment="Center"
                 TextAlignment="Center">
         <TextBlock.Text>
            <MultiBinding Converter="{StaticResource CapitalizationConverter}">
               <Binding RelativeSource="{RelativeSource TemplatedParent}" Path="AllCaps"/>
               <Binding RelativeSource="{RelativeSource TemplatedParent}" Path="Text"/>
            </MultiBinding>
         </TextBlock.Text>
      </TextBlock>
   </Border>
</ControlTemplate>

暴露另一个属性

另一种方法是公开一个只读依赖属性DisplayText。

private static readonly DependencyPropertyKey DisplayTextPropertyKey = DependencyProperty.RegisterReadOnly(
   nameof(DisplayText), typeof(string), typeof(TextButtonControl),
   new FrameworkPropertyMetadata(default(string), FrameworkPropertyMetadataOptions.None));

public static readonly DependencyProperty DisplayTextProperty = DisplayTextPropertyKey.DependencyProperty;

public string DisplayText
{
   get => (string)GetValue(DisplayTextProperty);
   private set => SetValue(DisplayTextPropertyKey, value);
}

当AllCaps 或Text 属性更改时，请重新格式化DisplayText 属性。这只是AllCaps 的示例，但它也适用于Text。

public static readonly DependencyProperty AllCapsProperty = DependencyProperty.Register(
   "AllCaps", typeof(bool), typeof(TextButtonControl), new PropertyMetadata(false, OnAllCapsChanged));

private static void OnAllCapsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
   var textButtonControl = (TextButtonControl)d;
   textButtonControl.DisplayText = textButtonControl.FormatText();
}

private string FormatText()
{
   return AllCaps ? Text.ToUpper() : Text.ToLower();
}

在您的控件模板中，您只需绑定到DisplayText。

<TextBlock Text="{Binding DisplayText, RelativeSource={RelativeSource TemplatedParent}}"
           FontFamily="{TemplateBinding FontFamily}"
           FontSize="{TemplateBinding FontSize}"
           VerticalAlignment="Center"
           HorizontalAlignment="Center"
           TextAlignment="Center"/>