问题描述
限时送ChatGPT账号..我正在为 ComboBox
控件编写一个自定义的 DataTemplateSelector
,我需要用它来为不同种类显示不同的 DateTemplates
对象,在 ComboBox
的关闭和打开模式下.
I'm writing a custom DataTemplateSelector
for a ComboBox
control and I'll need to use it to display different DateTemplates
for different kind of objects, in both the closed and open modes for the ComboBox
.
这是我想出的 DataTemplateSelector
:
public class ComboBoxTypedDataTemplateSelector : DataTemplateSelector
{
public IEnumerable<DataTemplate> SelectedTemplates { get; set; }
public IEnumerable<DataTemplate> DropDownTemplates { get; set; }
protected override DataTemplate SelectTemplateCore(object item, DependencyObject container)
{
IEnumerable<DataTemplate> source = container.FindParent<ComboBoxItem>() == null
? SelectedTemplates // Get the template for the closed mode
: DropDownTemplates; // Get the template for the open UI mode
Type type = item.GetType();
return null; // Some LINQ to get the first DataTemplate in source with the {x:DataType} that equals type
}
}
public sealed class DataTemplatesCollection : List<DataTemplate> { }
这是我在 XAML 中使用它的方式:
And here's how I'd use it in XAML:
<ComboBox>
<mvvm:ComboBoxTypedDataTemplateSelector>
<mvvm:ComboBoxTypedDataTemplateSelector.SelectedTemplates>
<mvvm:DataTemplatesCollection>
<DataTemplate x:DataType="models:SomeType">
<TextBlock Text="{x:Bind ...}"/>
</DataTemplate>
<DataTemplate x:DataType="models:SomeOtherType">
<TextBlock Text="{x:Bind ...}"/>
</DataTemplate>
</mvvm:DataTemplatesCollection>
</mvvm:ComboBoxTypedDataTemplateSelector.SelectedTemplates>
<mvvm:ComboBoxTypedDataTemplateSelector.DropDownTemplates>
<mvvm:DataTemplatesCollection>
<DataTemplate x:DataType="models:SomeType">
<TextBlock Text="{x:Bind ...}"/>
</DataTemplate>
<DataTemplate x:DataType="models:SomeOtherType">
<TextBlock Text="{x:Bind ...}"/>
</DataTemplate>
</mvvm:DataTemplatesCollection>
</mvvm:ComboBoxTypedDataTemplateSelector.DropDownTemplates>
</mvvm:ComboBoxTypedDataTemplateSelector>
</ComboBox>
现在,我唯一缺少的拼图是,我不知道如何在 C# 中获得 {x:DataType} 属性(我知道它实际上不是一个真正的属性,但我希望有一种方法通过代码检索它).我需要类似的东西才能从正确的模板组中为每个对象获取正确的 DataTemplate
.有什么方法可以实现吗?
Now, the only piece of the puzzle I'm missing, I can't figure out how to get that {x:DataType} property in C# (I know it's not actually a real property, but I hope there's a way to retrieve it via code).
I need something like that to be able to get the right DataTemplate
for each object, from the right templates group.
Is there a way I can achieve that?
注意:我知道我可以只编写一个特定的 DataTemplateSelector
,它具有要为每个项目类型返回的模板的硬编码名称,我可以使用该方法作为后备选项.但是,我想知道是否可以用这种方法编写一个更通用的选择器,以使其更加模块化并能够在未来重用它.
NOTE: I know I could just write a specific DataTemplateSelector
that has the hardcoded names of the templates to return for each item type, and I can use that method as a fallback option. But, I was wondering if it was possible to write a more generic selector with this approach in order to make it more modular and be able to reuse it in the future.
感谢您的帮助!
EDIT:按照 Vincent 的建议,我编写了一个附加属性来将给定的 Type
存储在 DataTemplate
中:
EDIT: following the suggestion by Vincent, I wrote an attached property to store a given Type
in a DataTemplate
:
public class DataTypeHelper
{
public static Type GetAttachedDataType(DataTemplate element)
{
return (Type)element.GetValue(AttachedDataTypeProperty);
}
public static void SetAttachedDataType(DataTemplate element, Type value)
{
element.SetValue(AttachedDataTypeProperty, value);
}
public static readonly DependencyProperty AttachedDataTypeProperty =
DependencyProperty.RegisterAttached("AttachedDataType", typeof(Type), typeof(DataTypeHelper), new PropertyMetadata(default(Type)));
}
我试过这样使用它:
...
<DataTemplate x:DataType="someXlmns:SomeClass"
mvvm:DataTypeHelper.AttachedDataType="someXlmns:SomeClass">
...
</DataTemplate>
但是我在将附加属性设置为我的类型的那一行收到了一个 XamlParseException
.我尝试将该属性设置为Grid"(作为测试)并且它不会崩溃,我不明白为什么它不能与我的自定义类型一起使用.
But I'm getting a XamlParseException
at the line where I set the attached property to my type. I've tried to set that property to "Grid" (just as a test) and it doesn't crash, I don't understand why isn't it working with my custom type.
EDIT #2:看起来 x:Type 标记扩展在 UWP 中不可用,我找不到另一种方法(我认为根本不可能)来获取类型直接来自 XAML 的实例,所以我只需要在 XAML 中使用类型名称,然后将其与模板选择器中的 item.GetType().Name
进行比较.
EDIT #2: looks like the x:Type markup extension is not available in UWP and I couldn't find another way (I don't think it's possible at all) to get a Type instance directly from XAML, so I had to just use the type name in XAML and then compare it to item.GetType().Name
in the template selector.
直接从 XAML 分配 Type 属性的能力会更好,因为它还可以在 XAML 设计器中进行语法/拼写检查,但至少这种方法可以正常工作.
The ability to assign a Type property directly from XAML would have been better as it'd also would have had syntax/spell-check in the XAML designer, but at least this approach works fine.
推荐答案
您无法检索此值.这只是提示编译器允许它为绑定生成适当的代码.
You cannot retrieve this value. This is just a hint for the compiler to allow it to generate the appropriate code for the binding.
您可以创建自定义附加属性来存储您需要的内容,也可以使用 Name 属性.
You can either create a custom attached property to store what you need or use the Name property.
<local:Selector x:Key="selector" >
<local:Selector.Template1>
<DataTemplate x:DataType="local:Item" x:Name="template1" >
<.../>
</DataTemplate>
</local:Selector.Template1>
</local:Selector>
然后在选择器实现中
Template1.GetValue(FrameworkElement.NameProperty);
这篇关于如何在 C# 中为自定义 DataTemplateSelector 获取 DataTemplate 的 {x:DataType}的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
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