传递命令参数
问题描述:
我试图传递一个命令参数与我的命令。我有一般的命令工作,但传递一个参数对我来说似乎不会很好。传递命令参数
我想从我的XAML中的分层数据传递用户名属性。我在这里做错了什么。
我收到和错误尝试用下面的命令语句来编译:
无法从 'lambda表达式' 到 'System.Action'
<HierarchicalDataTemplate
DataType="{x:Type viewModel:UsersViewModel}"
ItemsSource="{Binding Children}">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding UserName}">
<TextBlock.ContextMenu>
<ContextMenu>
<MenuItem Header="Edit" Command="{Binding EditCommand}" CommandParameter="{Binding UserName}"/>
<MenuItem Header="Delete"/>
</ContextMenu>
</TextBlock.ContextMenu>
</TextBlock>
</StackPanel>
</HierarchicalDataTemplate>
private RelayCommand _editCommand;
public ICommand EditCommand
{
get
{
if (_editCommand== null)
{
_editCommand= new RelayCommand(param => this.LoadUser(object parameter));
}
return _editCommand;
}
}
public void LoadUser(object username)
{
}
RelayCommand类转换
public class RelayCommand : ICommand
{
#region Fields
readonly Action<object> _execute;
readonly Predicate<object> _canExecute;
#endregion // Fields
#region Constructors
public RelayCommand(Action<object> execute)
: this(execute, null)
{
}
public RelayCommand(Action<object> execute, Predicate<object> canExecute)
{
if (execute == null)
throw new ArgumentNullException("execute");
_execute = execute;
_canExecute = canExecute;
}
#endregion // Constructors
#region ICommand Members
[DebuggerStepThrough]
public bool CanExecute(object parameter)
{
return _canExecute == null ? true : _canExecute(parameter);
}
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
public void Execute(object parameter)
{
_execute(parameter);
}
#endregion
}
感谢您的帮助!
答
new RelayCommand(param => this.LoadUser(object parameter));
不应该是这样:
new RelayCommand(param => this.LoadUser(param));
答
您不应该调用该方法,您应该将其作为参数传递。只需更换new RelayCommand(param => this.LoadUser(object parameter));
为new RelayCommand(this.LoadUser);
类似的问题在这里: RelayCommand lambda syntax problem
我明白了,我需要在拉姆达的 – rreeves 2012-02-06 22:58:11
@BatMasterson读了起来:有ISN对于那些简单的表达,'行动'只是无效的方法,右侧是方法体,你可以在其中执行任何你想做的事情。 ['Funcs'](http://msdn.microsoft.com/en-us/library/bb534960.aspx)将是具有返回值的方法。 – 2012-02-06 23:06:46