WinUI 3 (0.8.1)，C++/WinRT (2.0.210714.1)，桌面-使用“绑定操作：：集合绑定(...)
WinUI 3 (0.8.1)，C++/WinRT (2.0.210714.1)，桌面-使用“绑定操作：：集合绑定(...)
提问于 2021-07-20 22:48:08
我将Xaml中的一个ListBox绑定到一个NetworkViewModel实例，该实例包含一个NodeViewModel实例的集合。NodeViewModel实例需要在画布上显示在NodeViewModel提供的X和Y位置。
我想将ListBoxItem的Canvas.Left和Canvas.Top绑定到X和Y。我假设在WinUI中不可能在样式中使用绑定。变通方法可以是具有绑定的源路径的附加属性的帮助器类。它在后台代码中的帮助器属性的PropertyChangedCallback中创建绑定。但是绑定不起作用，为什么？
void BindingHelperNodes::OnBindingPathPropertyChanged( winrt::Microsoft::UI::Xaml::DependencyObject const& d,
winrt::Microsoft::UI::Xaml::DependencyPropertyChangedEventArgs const& e )
{
if(Microsoft::UI::Xaml::Controls::ListBoxItem item{ d.try_as<Microsoft::UI::Xaml::Controls::ListBoxItem>() })
{
Microsoft::UI::Xaml::Controls::Canvas::LeftProperty;
Microsoft::UI::Xaml::Data::Binding binding;
binding.Mode( Microsoft::UI::Xaml::Data::BindingMode::OneWay );
Microsoft::UI::Xaml::PropertyPath propertyPath( L"Y" );
binding.Path( propertyPath );
Microsoft::UI::Xaml::Data::RelativeSource relativeSource;
relativeSource.Mode( Microsoft::UI::Xaml::Data::RelativeSourceMode::Self );
binding.RelativeSource( relativeSource );
Microsoft::UI::Xaml::Data::BindingOperations::SetBinding(
d,
Microsoft::UI::Xaml::Controls::Canvas::LeftProperty(),
binding);
//item.SetBinding( Microsoft::UI::Xaml::Controls::Canvas::LeftProperty(), binding );
}
}
<Grid>
<Grid.Resources>
<ResourceDictionary>
<Style x:Name="listBoxItemContainerStyle2" TargetType="ListBoxItem">
<Setter Property="Canvas.Left" Value="0"/>
</Style>
</ResourceDictionary>
</Grid.Resources>
<ListBox Grid.Row="1" ItemsSource="{x:Bind mainViewModel.NetworkViewModel.Nodes, Mode=OneWay}"
>
<ItemsControl.ItemContainerStyle>
<Style TargetType="ListBoxItem">
<Setter Property="local:BindingHelperNodes.CanvasLeftBindingPath" Value="X"/>
</Style>
</ItemsControl.ItemContainerStyle>
<ListBox.Template>
<ControlTemplate TargetType="ListBox">
<ItemsPresenter />
</ControlTemplate>
</ListBox.Template>
<ListBox.ItemsPanel>
<ItemsPanelTemplate>
<Canvas Background="Transparent" />
</ItemsPanelTemplate>
</ListBox.ItemsPanel>
<ListBox.ItemTemplate>
<DataTemplate x:DataType="local:NodeViewModel">
<Grid
Width="120"
Height="60"
>
<!-- This rectangle is the main visual for the node. -->
<Rectangle
Stroke="Black"
Fill="White"
RadiusX="40"
RadiusY="40"
/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</Grid>回答 1
Stack Overflow用户
回答已采纳
发布于 2021-07-20 23:43:14
我很幸运地发现了问题所在！真正的问题是对第13行中的SetBinding()的调用，它没有任何效果。但是我实际上忘记了在IDL文件中设置属性"Microsoft.UI.Xaml.Data.Bindable“！
IDL文件：
namespace NetworkView
{
[Microsoft.UI.Xaml.Data.Bindable]
runtimeclass NodeViewModel : Microsoft.UI.Xaml.Data.INotifyPropertyChanged
{
// Declaring a constructor (or constructors) in the IDL causes the runtime class to be
// activatable from outside the compilation unit.
NodeViewModel();
String Name;
Double X;
Double Y;
}
}用于创建绑定的CPP文件：
void BindingHelperNodes::OnBindingPathPropertyChanged( winrt::Microsoft::UI::Xaml::DependencyObject const& d, winrt::Microsoft::UI::Xaml::DependencyPropertyChangedEventArgs const& e )
{
if(Microsoft::UI::Xaml::Controls::ListBoxItem item{ d.try_as<Microsoft::UI::Xaml::Controls::ListBoxItem>() })
{
Microsoft::UI::Xaml::Data::Binding binding;
binding.Mode( Microsoft::UI::Xaml::Data::BindingMode::OneWay );
Microsoft::UI::Xaml::PropertyPath propertyPath( L"X" );
binding.Path( propertyPath );
// Alternative 1 works
//Microsoft::UI::Xaml::Data::BindingOperations::SetBinding(
// d,
// Microsoft::UI::Xaml::Controls::Canvas::LeftProperty(),
// binding);
// Alternative 2 works, too
item.SetBinding( Microsoft::UI::Xaml::Controls::Canvas::LeftProperty(), binding );
}
}向Alfred致以最好的问候
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原文链接：
https://stackoverflow.com/questions/68456935
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