[英]Handling input gestures in a user control (MVVM)
使用MVVM模式,如何处理按键手势?
UserControl.InputBindings无法工作,因为它无法聚焦。
我定义了一个ICommand,当键入正确的键时应该调用该ICommand,但是如何将命令与View连接起来却迷茫了。
谢谢,Stefan
我通过创建DelegateCommand类解决了这个问题。 它看起来完全像RelayCommand(请参见Josh Smith),但它允许更新回调。
public class DelegateCommand : ICommand
{
Action<object> _execute;
Predicate<object> _canExecute;
#region Constructors
public DelegateCommand()
{
}
public DelegateCommand(Action<object> execute)
: this(execute, null)
{
}
public DelegateCommand(Action<object> execute, Predicate<object> canExecute)
{
if (execute == null)
throw new ArgumentNullException("execute");
_execute = execute;
_canExecute = canExecute;
}
#endregion // Constructors
public void Delegate(Action<object> execute)
{
_execute = execute;
}
public void Delegate(Action<object> execute, Predicate<object> canExecute)
{
_execute = execute;
_canExecute = canExecute;
}
#region ICommand Members
[DebuggerStepThrough]
public bool CanExecute(object parameter)
{
return _canExecute == null ? _execute != null : _canExecute(parameter);
}
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
public void Execute(object parameter)
{
if (CanExecute(parameter))
_execute(parameter);
}
#endregion // ICommand Members
}
然后,我创建了一个用于容纳静态应用程序命令的类。
public class CustomCommands
{
private readonly static DelegateCommand admin;
static CustomCommands()
{
admin = new DelegateCommand();
}
public static DelegateCommand AdminCommand
{
get { return admin; }
}
}
然后,由于用户控件未收到按键手势,我向主窗口添加了按键绑定。
<Window.InputBindings>
<KeyBinding Key="A" Modifiers="Control" Command="my:CustomCommands.AdminCommand"/>
</Window.InputBindings>
然后,在我的ViewModel中,我可以像这样处理事件:
public class OfflineViewModel : ViewModelBase
{
public OfflineViewModel()
{
CustomCommands.AdminCommand.Delegate(ShowAdmin);
}
public override void Removed()
{
base.Removed();
ReleaseAdminCommand();
}
public override void Hidden()
{
base.Hidden();
ReleaseAdminCommand();
}
void HookAdminCommand()
{
CustomCommands.AdminCommand.Delegate(ShowAdmin);
}
void ReleaseAdminCommand()
{
// Remove handling
CustomCommands.AdminCommand.Delegate(null, null);
}
void ShowAdmin(object parameter)
{
Navigation.Push(new AdminViewModel());
}
}
(可选)我可以在DelegateCommand内部使用事件。
这对我有效(.Net 4.0)
<UserControl>
<UserControl.InputBindings>
<KeyBinding Gesture="CTRL+C" Command="{Binding CancelCommand}" />
<KeyBinding Gesture="F5" Command="{Binding StartCommand}" />
<KeyBinding Gesture="CTRL+F5" Command="{Binding FreshStartCommand}" />
<KeyBinding Gesture="F10" Command="{Binding ContinueCommand}" />
<KeyBinding Gesture="F9" Command="{Binding RepeatCommand}" />
<KeyBinding Gesture="ALT+F4" Command="{Binding CloseCommand}" />
<KeyBinding Gesture="CTRL+N" Command="{Binding NewUUTCommand}" />
</UserControl.InputBindings>
....
<StackPanel DockPanel.Dock="Bottom" Orientation="Horizontal" HorizontalAlignment="Center">
<Button x:Name="BtnStart" Content="STARTEN" Command="{Binding StartCommand}"/>
<Button Content="STOP" Command="{Binding StopCommand}"/>
</StackPanel>
....
<FocusManager.FocusedElement>
<Binding ElementName="BtnStart"/>
</FocusManager.FocusedElement>
</UserControl>
技巧是确保将焦点设置到UserControl中。 对我来说,这不是自动发生的。 一旦设置了焦点,则KeyBinding将起作用。 (注意,焦点必须设置在最后,因为必须先定义元素)
为了完整起见,这是ViewModel代码。
public ICommand StartCommand
{
get
{
if (this._startCommand == null)
{
this._startCommand = new Mvvm.RelayCommand(parm => DoStart(), parm => DoCanStart());
} return this._startCommand;
}
}
private bool DoCanStart()
{
return !IsRunning && ReadyToRun;
}
private void DoStart()
{
log.Debug("Start test");
...
}
请看以下示例: http : //tomlev2.wordpress.com/2009/03/17/wpf-using-inputbindings-with-the-mvvm-pattern/
它使用XML标记将其绑定到DataContext of the root element
。 希望对您有帮助。
此解决方案有一个局限性:它仅适用于XAML根的DataContext。 因此,例如,您不能使用它在其DataContext也被重新定义的控件上定义InputBinding,因为标记扩展将访问根DataContext。
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