我想实现值转换器来为RenderTransform指定Point。这工作正常,直到我只是实现IValueConverter接口。我知道我可以实现MarkupExtension类,以便每次都不为我的转换器声明分离的XAML资源。当我尝试实现这个时,我有
InvalidCastException:无法将类型为“System.Object”的对象强制转换为“System.Windows.Data.IValueConverter”。
转换器实施:
[ValueConversion(typeof(Point), typeof(Transform))]
public class PointToTransformConverter : MarkupExtension, IValueConverter
{
private PointToTransformConverter _instance = null;
public object Convert(
object value,
Type targetType,
object parameter,
CultureInfo culture)
{
var point = (Point)value;
return new TransformGroup
{
Children = new TransformCollection
{
new TranslateTransform(point.X, point.Y)
}
};
}
public object ConvertBack(
object value,
Type targetType,
object parameter,
CultureInfo culture)
{
var transform = value as TransformGroup;
if (transform?.Children.Count > 0)
{
var translateTransform = transform.Children[0] as TranslateTransform;
if (translateTransform != null)
{
return new Point(
translateTransform.X,
translateTransform.Y);
}
}
return null;
}
public override object ProvideValue(IServiceProvider serviceProvider)
{
return _instance ?? (_instance = new PointToTransformConverter());
}
}
XAML用法:
<local:PathControl x:Class="PathToWiringTube.PathView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:PathToWiringTube"
xmlns:view="clr-namespace:PathToWiringTube.View"
xmlns:vm="clr-namespace:PathToWiringTube.VM"
xmlns:crocodile="clr-namespace:Crocodile;assembly=Crocodile"
mc:Ignorable="d"
d:DataContext="{d:DesignInstance vm:PathVm}">
<local:PathControl.Resources>
<crocodile:PointToTransformConverter x:Key="pointToTransformConverter"/>
</local:PathControl.Resources>
<Canvas>
<ItemsControl x:Name="itemsMarkers" ItemsSource="{Binding Markers}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<view:SplineDensityMarker Width="5" RenderTransform="{Binding Position, Converter={StaticResource pointToTransformConverter}}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</Canvas>
</local:PathControl>
我做错了什么?
答案 0 :(得分:1)
请您尝试下面的代码并检查异常是否即将到来? 我纠正了它。实例应该是静态的和xaml,您可以直接引用转换器而不是将其称为静态资源。这是使用 MarkupExtension 的主要用途。下面的代码应该可以正常工作。如有任何问题,请恢复。
转换器:
[ValueConversion(typeof(Point), typeof(Transform))]
public class PointToTransformConverter : MarkupExtension, IValueConverter
{
private static PointToTransformConverter _instance = null;
public object Convert(
object value,
Type targetType,
object parameter,
CultureInfo culture)
{
var point = (Point)value;
return new TransformGroup
{
Children = new TransformCollection
{
new TranslateTransform(point.X, point.Y)
}
};
}
public object ConvertBack(
object value,
Type targetType,
object parameter,
CultureInfo culture)
{
var transform = value as TransformGroup;
if (transform?.Children.Count > 0)
{
var translateTransform = transform.Children[0] as TranslateTransform;
if (translateTransform != null)
{
return new Point(
translateTransform.X,
translateTransform.Y);
}
}
return null;
}
public override object ProvideValue(IServiceProvider serviceProvider)
{
return _instance ?? (_instance = new PointToTransformConverter());
}
}
Xaml:
<local:PathControl x:Class="PathToWiringTube.PathView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:PathToWiringTube"
xmlns:view="clr-namespace:PathToWiringTube.View"
xmlns:vm="clr-namespace:PathToWiringTube.VM"
xmlns:crocodile="clr-namespace:Crocodile;assembly=Crocodile"
mc:Ignorable="d"
d:DataContext="{d:DesignInstance vm:PathVm}">
</local:PathControl.Resources>
<Canvas>
<ItemsControl x:Name="itemsMarkers" ItemsSource="{Binding Markers}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<view:SplineDensityMarker Width="5" RenderTransform="{Binding Position, Converter={crocodile:PointToTransformConverter}}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</Canvas>
</local:PathControl>
答案 1 :(得分:0)
我在另一个环境中检查了我的代码并检测到它有效。我已经完成了Visual Studio版本不匹配的研究并找到了它(14.0.23107.0 D14REL和14.0.24720.00 Update1)。在我的旧环境中安装最新的Visual Studio Update 2后,一切正常。