silverlight - 根据属性值更改 VisualState

Question

如何根据 WP7 上的属性值更改 VisualState？

我尝试使用 MVVM 模式，当我的模型加载时，我希望我的 View 转到特定的 VisualState。

在 Silverlight 中，我们有属性更改的触发器，但在 WP7 中没有!

PS:我不想使用框架我想了解它是如何在 WP7 中完成的。

Answer 1

我使用以下附加行为:

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 ) );
        }
    }
}

在您的 View 模型中，公开当前视觉状态的属性，然后在要为您处理视觉状态的视觉元素上使用以下内容绑定(bind)视觉状态，例如

<phone:PhoneApplicationPage ...
    xmlns:common="clr-namespace:PixelLab.Common;assembly=PixelLab.Common"
    common:VisualStates.CurrentState="{Binding CurrentState}">