如何根据属性值在WP7上更改VisualState?
我正在尝试使用MVVM模式,当我的模型正在加载时,我希望我的视图进入特定的VisualState。
在Silverlight中,我们可以使用触发器来检测属性变化,但在WP7中没有这个功能!
注:我不想使用框架,我想了解在WP7中如何实现。
如何根据属性值在WP7上更改VisualState?
我正在尝试使用MVVM模式,当我的模型正在加载时,我希望我的视图进入特定的VisualState。
在Silverlight中,我们可以使用触发器来检测属性变化,但在WP7中没有这个功能!
注:我不想使用框架,我想了解在WP7中如何实现。
using System;
using System.Windows;
using System.Windows.Controls;
namespace PixelLab.WP7.Common.Behaviors
{
///
/// Provides an attached behavior for binding visual states.
///
public static class VisualStates
{
///
/// Identifies the CurrentState attached property.
///
public static readonly DependencyProperty CurrentStateProperty = DependencyProperty
.RegisterAttached(
"CurrentState",
typeof(string),
typeof(VisualStates),
new PropertyMetadata(TransitionToState));
///
/// Gets the current visual state of the specified object. This is an attached property.
///
/// The source object.
/// The current visual state of the specified object.
public static string GetCurrentState(DependencyObject obj)
{
return (string)obj.GetValue(CurrentStateProperty);
}
///
/// Sets the current visual state of the specified object. This is an attached property.
///
/// The target object.
/// The new visual state.
public static void SetCurrentState(DependencyObject obj, string value)
{
obj.SetValue(CurrentStateProperty, value);
}
static void startOnGuiThread( Action act )
{
var disp = Deployment.Current.Dispatcher;
if( disp.CheckAccess() )
act();
else
disp.BeginInvoke( act );
}
private static void TransitionToState( object sender, DependencyPropertyChangedEventArgs args )
{
FrameworkElement elt = sender as FrameworkElement;
if( null == elt )
throw new ArgumentException( "CurrentState is only supported on the FrameworkElement" );
string newState = args.NewValue.ToString();
startOnGuiThread( () => ExtendedVisualStateManager.GoToElementState( elt, newState, true ) );
}
}
}
<phone:PhoneApplicationPage ...
xmlns:common="clr-namespace:PixelLab.Common;assembly=PixelLab.Common"
common:VisualStates.CurrentState="{Binding CurrentState}">
最初DataStateBehavior行为看起来是完美的匹配,而且this article甚至专门讨论了如何在WP7中使用它。
然而,文章引用的Codeplex项目不再具有该行为,并且该行为不适用于Expression Blend(至少对于WP7项目)。
我倾向于在ViewModel上公开一个属性,并以编程方式监听View中的更改并相应地更改Visual State:
在您的View的构造函数中:
ViewModelLocator.MainViewModelStatic.PropertyChanged += ViewModelPropertyChanged;
然后创建一个事件处理程序,相应地更改状态:
private void ViewModelPropertyChanged(object sender, PropertyChangedEventArgs e)
{
if(e.PropertyName == MainViewModel.SomeProp)
{
// Change the state using the VisualStateManager
}
}
达米安