我有一个窗口,基本上运行一个计时器。当计时器归零时,我希望将窗口置于最前面,以便它可见,而不是隐藏在其他应用程序后面。
据我所知,我只需调用window.activate()就可以实现这一点,但是使用mvvm时,我的视图模型没有对窗口的引用。
一个“纯粹”的MVVM解决方案是使用行为(behavior)。下面是一个针对Window
和Activated
属性的行为。将该属性设置为true将激活窗口(如果窗口被最小化,则会还原):
public class ActivateBehavior : Behavior<Window> {
Boolean isActivated;
public static readonly DependencyProperty ActivatedProperty =
DependencyProperty.Register(
"Activated",
typeof(Boolean),
typeof(ActivateBehavior),
new PropertyMetadata(OnActivatedChanged)
);
public Boolean Activated {
get { return (Boolean) GetValue(ActivatedProperty); }
set { SetValue(ActivatedProperty, value); }
}
static void OnActivatedChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e) {
var behavior = (ActivateBehavior) dependencyObject;
if (!behavior.Activated || behavior.isActivated)
return;
// The Activated property is set to true but the Activated event (tracked by the
// isActivated field) hasn't been fired. Go ahead and activate the window.
if (behavior.AssociatedObject.WindowState == WindowState.Minimized)
behavior.AssociatedObject.WindowState = WindowState.Normal;
behavior.AssociatedObject.Activate();
}
protected override void OnAttached() {
AssociatedObject.Activated += OnActivated;
AssociatedObject.Deactivated += OnDeactivated;
}
protected override void OnDetaching() {
AssociatedObject.Activated -= OnActivated;
AssociatedObject.Deactivated -= OnDeactivated;
}
void OnActivated(Object sender, EventArgs eventArgs) {
this.isActivated = true;
Activated = true;
}
void OnDeactivated(Object sender, EventArgs eventArgs) {
this.isActivated = false;
Activated = false;
}
}
这种行为需要引用System.Windows.Interactivity.dll
。幸运的是,现在可以在NuGet上通过Blend.Interactivity.Wpf包获得此引用。
该行为在XAML中附加到窗口如下:
<Window ...>
<i:Interaction.Behaviors>
<Behaviors:ActivateBehavior Activated="{Binding Activated, Mode=TwoWay}"/>
</i:Interaction.Behaviors>
Activated
属性。将此属性设置为true将激活窗口(除非它已经处于激活状态)。作为额外奖励,它还将恢复最小化的窗口。class SomeView
{
void HandleSomeCommandOrEvent()
{
this.Activate();
}
}
public partial class MainWindow : Window
{
MainWindowViewModel ViewModel { get; set; }
public MainWindow()
{
InitializeComponent();
ViewModel = new MainWindowViewModel();
ViewModel.ShowMessage += ViewModel_ShowMessage;
this.DataContext = ViewModel;
}
void ViewModel_ShowMessage(object sender, ShowMessageEventArgs e)
{
MessageBox.Show(e.Message, "Some caption", MessageBoxButton.OK);
}
}
// The view model
public class MainWindowViewModel
{
// The button click command
public RelayCommand ButtonClickCommand { get; set; }
// The event to fire
public event EventHandler<ShowMessageEventArgs> ShowMessage;
public MainWindowViewModel()
{
ButtonClickCommand = new RelayCommand(ButtonClicked);
}
void ButtonClicked(object param)
{
// This button is wired up in the view as normal and fires the event
OnShowMessage("You clicked the button");
}
// Fire the event - it's up to the view to decide how to implement this event and show a message
void OnShowMessage(string message)
{
if (ShowMessage != null) ShowMessage(this, new ShowMessageEventArgs(message));
}
}
public class ShowMessageEventArgs : EventArgs
{
public string Message { get; private set; }
public ShowMessageEventArgs(string message)
{
Message = message;
}
}
XAML 将是:
<Button Command="{Binding ButtonClickCommand}">Click me!</Button>
我会选择这个方向:
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;
using GalaSoft.MvvmLight.Messaging;
// View
public partial class TestActivateWindow : Window
{
public TestActivateWindow() {
InitializeComponent();
Messenger.Default.Register<ActivateWindowMsg>(this, (msg) => Activate());
}
}
// View Model
public class MainViewModel: ViewModelBase
{
ICommand _activateChildWindowCommand;
public ICommand ActivateChildWindowCommand {
get {
return _activateChildWindowCommand?? (_activateChildWindowCommand = new RelayCommand(() => {
Messenger.Default.Send(new ActivateWindowMsg());
}));
}
}
}
public class ActivateWindowMsg
{
}