wp7、8丿____IValueConverter_(含参,值转换器)

示例：

using System;
using System.Globalization;
using System.Windows.Data;
using System.Windows.Media;

namespace Sounds
{
    /// <summary>
    /// 此转换器：实现MediaElementState类型的转换为Boolean类型
    /// </summary>
    public class AudioStateConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            MediaElementState testState;
            if (parameter is MediaElementState)
            {
                testState = (MediaElementState)parameter;
            }
            else
            {
                testState = (MediaElementState)Enum.ToObject(typeof(MediaElementState), parameter);
            }
            var state = (MediaElementState)value;
            var matched = state == testState;
            return matched;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotSupportedException();
        }
    }
}

<phone:PhoneApplicationPage
    .................
    xmlns:local="clr-namespace:Sounds">

    <phone:PhoneApplicationPage.Resources>
        <local:TimeSpanConverter x:Key="TimeSpanConverter"/>
        <MediaElementState x:Key="playing_state">Playing</MediaElementState>
        <MediaElementState x:Key="stopped_state">Stopped</MediaElementState>
        <local:AudioStateConverter x:Key="AudioStateConverter"/>
    </phone:PhoneApplicationPage.Resources>

<MediaElement x:Name="VideoPlayer" AutoPlay="True" 
    Source="Wildlife.wmv" >
    <MediaElement.Clip>
        <RectangleGeometry RadiusY="0" RadiusX="0" Rect="30,30,100,85">
            <RectangleGeometry.Transform>
                <CompositeTransform Rotation="-5" CenterX="130" CenterY="75" />
            </RectangleGeometry.Transform>
        </RectangleGeometry>
    </MediaElement.Clip>

</MediaElement>
<local:MediaElementBinder x:Name="MediaBinder" MediaElement="{Binding ElementName=VideoPlayer}"/>
<Button x:Name="VideoPlayButton" Content="Play" Height="70" Margin="0,140,0,0" Width="168" VerticalAlignment="Top" HorizontalAlignment="Left" Click="VideoPlayButton_Click" IsEnabled="{Binding CurrentState, ConverterParameter={StaticResource stopped_state}, Converter={StaticResource AudioStateConverter}, ElementName=MediaBinder}" />
<Button x:Name="VideoStopButton" Content="Stop" Height="70" Margin="0,212,0,0" Width="168" VerticalAlignment="Top" HorizontalAlignment="Left" Click="VideoStopButton_Click" IsEnabled="{Binding CurrentState, ConverterParameter={StaticResource playing_state}, Converter={StaticResource AudioStateConverter}, ElementName=MediaBinder}" />

 由于MediaElement很多属性直接绑定是不会变的，所以增加一些辅助类

using System.Windows;
using System.Windows.Controls;
using System.Windows.Interactivity;
using System.Windows.Media;
using System.ComponentModel;
using System.Windows.Threading;
using System;

namespace Sounds
{
    public class MediaElementBinder : FrameworkElement
    {
        private DispatcherTimer timer = new DispatcherTimer();

        public MediaElementBinder()
        {
            // Timer interval 200 milliseconds
            timer.Interval = new TimeSpan(0, 0, 0, 0, 200);
            timer.Tick += timer_Tick;
        }

        void timer_Tick(object sender, EventArgs e)
        {
            this.Position = this.MediaElement.Position;
        }

        public MediaElement MediaElement
        {
            get { return (MediaElement)GetValue(MediaElementProperty); }
            set { SetValue(MediaElementProperty, value); }
        }
        public static readonly DependencyProperty MediaElementProperty =
            DependencyProperty.Register(
                "MediaElement",
                typeof(MediaElement),
                typeof(MediaElementBinder),
                new PropertyMetadata(OnMediaElementChanged));
        private static void OnMediaElementChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
        {
            var mediator = (MediaElementBinder)o;
            var mediaElement = (MediaElement)(e.NewValue);
            if (null != mediaElement)
            {
                mediaElement.CurrentStateChanged += mediator.MediaPlayer_CurrentStateChanged;
                mediaElement.MediaOpened += mediator.MediaPlayer_MediaOpened;
            }
        }

        
       
        public MediaElementState CurrentState
        {
            get { return (MediaElementState)GetValue(CurrentStateProperty); }
            set { SetValue(CurrentStateProperty, value); }
        }

        public static readonly DependencyProperty CurrentStateProperty =
            DependencyProperty.Register("CurrentState", typeof(MediaElementState), typeof(MediaElementBinder), new PropertyMetadata(null));




        public TimeSpan Position
        {
            get { return (TimeSpan)GetValue(PositionProperty); }
            set { SetValue(PositionProperty, value); }
        }

        // Using a DependencyProperty as the backing store for Position.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty PositionProperty =
            DependencyProperty.Register("Position", typeof(TimeSpan), typeof(MediaElementBinder), new PropertyMetadata(null));



        public Duration Duration
        {
            get { return (Duration)GetValue(DurationProperty); }
            set { SetValue(DurationProperty, value); }
        }

        // Using a DependencyProperty as the backing store for Duration.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty DurationProperty =
            DependencyProperty.Register("Duration", typeof(Duration), typeof(MediaElementBinder), new PropertyMetadata(null));


        private void MediaPlayer_MediaOpened(object sender, RoutedEventArgs e)
        {
            var element =sender as MediaElement;
            this.Duration = element.NaturalDuration;
        }        


        private void MediaPlayer_CurrentStateChanged(object sender, System.Windows.RoutedEventArgs e)
        {
            this.CurrentState = (sender as MediaElement).CurrentState;

            if (this.CurrentState == MediaElementState.Playing)
            {
                timer.Start();
            }
            else
            {
                timer.Stop();
            }
        }
        
    }
}