我尝试创建继承自DependencyObject和ICommand的Command。我有以下代码:
public class CustomCommand : DependencyObject, ICommand
{
public static readonly DependencyProperty CommandProperty;
public static readonly DependencyProperty AfterCommandProperty;
static CustomCommand()
{
var ownerType = typeof(CustomCommand);
CommandProperty = DependencyProperty.RegisterAttached("Command", typeof(Action), ownerType, new PropertyMetadata(null));
AfterCommandProperty = DependencyProperty.RegisterAttached("AfterCommand", typeof(Action), ownerType, new PropertyMetadata(null));
}
public Action Command
{
get => (Action)GetValue(CommandProperty);
set => SetValue(CommandProperty, value);
}
public Action AfterCommand
{
get => (Action)GetValue(CommandProperty);
set => SetValue(CommandProperty, value);
}
public bool CanExecute(object parameter)
{
return true;
}
public void Execute(object parameter)
{
// Command & AfterCommand are always null
}
}
和
<Button Content="Test">
<Button.Command>
<command:CustomCommand Command="{Binding Copy}" AfterCommand="{Binding AfterCopy}" />
</Button.Command>
</Button>
当我按下测试按钮命令且 AfterCommand 为空时。你有好主意吗 ?什么是最好的方法,因为我无法将ICommand引用添加到我的ViewModel。
由于
答案 0 :(得分:0)
您的CustomCommand实例不在可视树中,因此绑定是一个问题。它无法获得DataContext。尝试对绑定进行跟踪:
<Button.Command>
<local:CustomCommand
Command="{Binding TestAction, PresentationTraceSources.TraceLevel=High}"
/>
</Button.Command>
“找不到框架导师”是您在调试输出中看到的错误。 “雅不能从这里到达那里”是他们怎么说Down East。 XAML中的上下文是父母对父母的问题,但从某种意义上来说,这个问题与父母无关。
但这很容易解决。使用绑定代理。这是我从various questions and answers on Stack Overflow多次偷走的城镇自行车实施:
public class BindingProxy : Freezable
{
protected override Freezable CreateInstanceCore()
{
return new BindingProxy();
}
public object Data
{
get { return (object)GetValue(DataProperty); }
set { SetValue(DataProperty, value); }
}
// Using a DependencyProperty as the backing store for Data. This enables animation, styling, binding, etc...
public static readonly DependencyProperty DataProperty =
DependencyProperty.Register("Data", typeof(object), typeof(BindingProxy), new UIPropertyMetadata(null));
}
将实例定义为某个包含范围的资源,该范围具有所需DataContext
属性所在的Action
。没有路径的{Binding}
只返回DataContext
,这将是下面案例中窗口的viewmodel。
<Window.Resources>
<local:BindingProxy
x:Key="MainViewModelBindingProxy"
Data="{Binding}"
/>
</Window.Resources>
并像这样使用它。 Data
的{{1}}属性绑定到viewmodel,因此请使用BindingProxy
的路径。我打电话给我的Data.WhateverPropertyYouWant
财产Action
。
TestAction
您的<Button
Content="Custom Command Test"
>
<Button.Command>
<local:CustomCommand
Command="{Binding Data.TestAction, Source={StaticResource MainViewModelBindingProxy}}"
/>
</Button.Command>
</Button>
媒体资源中也有一个错误:它正在将AfterCommand
传递给GetValue / SetValue,而不是CommandProperty
。