我在理解命令参数绑定的工作原理时遇到了一些麻烦。WPF CommandParameter绑定问题
当我在调用InitializeComponent之前创建一个widget类的实例时,它似乎工作正常。对ExecuteCommand函数中参数(Widget)的修改将被“应用”到_widget。这是我期望的行为。
如果_widget的实例是在InitializeComponent之后创建的,那么我会在ExecuteCommand函数中获得e.Parameter的空引用异常。
这是为什么?如何使用MVP模式进行这项工作,在创建视图之后绑定对象可能会创建?
public partial class WidgetView : Window
{
RoutedCommand _doSomethingCommand = new RoutedCommand();
Widget _widget;
public WidgetView()
{
_widget = new Widget();
InitializeComponent();
this.CommandBindings.Add(new CommandBinding(DoSomethingCommand, ExecuteCommand, CanExecuteCommand));
}
public Widget TestWidget
{
get { return _widget; }
set { _widget = value; }
}
public RoutedCommand DoSomethingCommand
{
get { return _doSomethingCommand; }
}
private static void CanExecuteCommand(object sender, CanExecuteRoutedEventArgs e)
{
if (e.Parameter == null)
e.CanExecute = true;
else
{
e.CanExecute = ((Widget)e.Parameter).Count < 2;
}
}
private static void ExecuteCommand(object sender, ExecutedRoutedEventArgs e)
{
((Widget)e.Parameter).DoSomething();
}
}
<Window x:Class="CommandParameterTest.WidgetView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="WidgetView" Height="300" Width="300"
DataContext="{Binding RelativeSource={RelativeSource Self}}">
<StackPanel>
<Button Name="_Button" Command="{Binding DoSomethingCommand}"
CommandParameter="{Binding TestWidget}">Do Something</Button>
</StackPanel>
</Window>
public class Widget
{
public int Count = 0;
public void DoSomething()
{
Count++;
}
}