XAML中如何基于绑定选择画笔

Question

我在 Application.xaml 中定义了数百个画笔。这些是项目中多个用户控件的共享资源。它们都有图案键：ch_YSD、ch_HJU、ch_IYO...

我尝试在数据模板中使用这些画笔。在数据模板中，我可以访问画笔键的可变部分，即在数据模板中，我可以将 YSD、HJU、IYO 等作为字符串。

如何从 xaml 绑定到特定的画笔资源？

目前我有这样的解决方案：在样式中使用数据触发器根据绑定的字符串（键的可变部分）将所需的属性设置为指定的画笔。 我对这个解决方案不满意，因为 Application.xaml 中的画笔列表会经常增加。

我不确定是否应该使用后面的代码，因为我想在 Application.xaml 中使用共享资源的内存节省优势。

Answer 1

这是一种看似简单但实际上没有完美解决方案的任务（或者我没有找到）。第一种方法是使用值转换器。但它不起作用！我们需要设置转换器无法正确完成的资源引用。所以，我认为正确的方法是依附行为。但是您应该了解限制：只能将资源应用于一个属性。也许您可以根据您的要求避免此限制。

附加行为允许您将具有指定名称的资源引用到指定的依赖属性：

public static class BrushResourceKeyBehavior
{
    #region ResourceKey Property

    public static readonly DependencyProperty ResourceKeyProperty = DependencyProperty.RegisterAttached(
        "ResourceKey", typeof(object), typeof(BrushResourceKeyBehavior),
        new FrameworkPropertyMetadata(OnResourceKeyChanged));

    public static object GetResourceKey(DependencyObject dependencyObject)
    {
        return dependencyObject.GetValue(ResourceKeyProperty);
    }

    public static void SetSource(DependencyObject dependencyObject, object value)
    {
        dependencyObject.SetValue(ResourceKeyProperty, value);
    }

    #endregion

    #region TargetProperty Property

    public static readonly DependencyProperty TargetPropertyProperty = DependencyProperty.RegisterAttached(
        "TargetProperty", typeof(DependencyProperty), typeof(BrushResourceKeyBehavior),
        new FrameworkPropertyMetadata(OnTargetPropertyChanged));

    public static DependencyProperty GetTargetProperty(DependencyObject dependencyObject)
    {
        return (DependencyProperty)dependencyObject.GetValue(TargetPropertyProperty);
    }

    public static void SetTargetProperty(DependencyObject dependencyObject, DependencyProperty value)
    {
        dependencyObject.SetValue(TargetPropertyProperty, value);
    }

    #endregion

    private static void OnResourceKeyChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
    {
        var targetProperty = GetTargetProperty(dependencyObject);
        if (targetProperty != null)
        {
            if (e.NewValue == null)
            {
                dependencyObject.ClearValue(targetProperty);
            }
            else
            {
                SetResourceReference(dependencyObject, targetProperty);
            }
        }
    }

    private static void OnTargetPropertyChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
    {
        var oldValue = e.OldValue as DependencyProperty;
        var newValue = e.NewValue as DependencyProperty;

        if (oldValue != null)
        {
            dependencyObject.ClearValue(oldValue);
        }

        if (newValue != null)
        {
            SetResourceReference(dependencyObject, newValue);
        }
    }

    private static void SetResourceReference(DependencyObject dependencyObject, DependencyProperty targetProperty)
    {
        var fe = dependencyObject as FrameworkElement;
        if (fe != null)
        {
            fe.SetResourceReference(targetProperty, String.Format("ch_{0}", GetResourceKey(fe)));
        }
        else
        {
            var fce = dependencyObject as FrameworkContentElement;
            if (fce != null)
            {
                fce.SetResourceReference(targetProperty, String.Format("ch_{0}", GetResourceKey(fce)));
            }
        }
    }
}

行为可以在 XAML 中使用，如下所示：

<ItemsControl>
    <Border local:BrushResourceKeyBehavior.Source="YSD"
            local:BrushResourceKeyBehavior.TargetProperty="Border.Background"
            Height="20"/>
    <Border local:BrushResourceKeyBehavior.Source="HJU"
            local:BrushResourceKeyBehavior.TargetProperty="Border.Background"
            Height="20"/>
    <Border local:BrushResourceKeyBehavior.Source="IYO"
            local:BrushResourceKeyBehavior.TargetProperty="Border.Background"
            Height="20"/>
</ItemsControl>

上面的代码相当于：

<ItemsControl>
    <Border Background="{DynamicResource ch_YSD}"
            Height="20"/>
    <Border Background="{DynamicResource ch_HJU}"
            Height="20"/>
    <Border Background="{DynamicResource ch_IYO}"
            Height="20"/>
</ItemsControl>