Procedura: Controllare un oggetto MediaElement (Play, Pause, Stop, Volume e Speed)

Nell'esempio seguente viene illustrato come controllare la riproduzione di elementi multimediali usando un MediaElement. Nell'esempio viene creato un semplice lettore multimediale che consente di riprodurre, sospendere, arrestare e saltare avanti e indietro nel contenuto multimediale, nonché regolare il volume e il rapporto di velocità di riproduzione.

Creare l'interfaccia utente

Il codice seguente crea l'interfaccia utente.

<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  x:Class="SDKSample.MediaElementExample" >

  <StackPanel Background="Black">

    <!-- To interactively stop, pause, and play the media, the LoadedBehavior 
           property of the MediaElement must be set to "Manual". -->
    <MediaElement Source="media\numbers.wmv" Name="myMediaElement" 
     Width="450" Height="250" LoadedBehavior="Manual" UnloadedBehavior="Stop" Stretch="Fill" 
     MediaOpened="Element_MediaOpened" MediaEnded="Element_MediaEnded"/>
    
    <StackPanel HorizontalAlignment="Center" Width="450" Orientation="Horizontal">

      <!-- Play button. -->
      <Image Source="images\UI_play.gif" MouseDown="OnMouseDownPlayMedia" Margin="5" />

      <!-- Pause button. -->
      <Image Source="images\UI_pause.gif" MouseDown="OnMouseDownPauseMedia" Margin="5" />

      <!-- Stop button. -->
      <Image Source="images\UI_stop.gif" MouseDown="OnMouseDownStopMedia" Margin="5" />

      <!-- Volume slider. This slider allows a Volume range between 0 and 1. -->
      <TextBlock Foreground="White" VerticalAlignment="Center" Margin="5"  >Volume</TextBlock>
      <Slider Name="volumeSlider" VerticalAlignment="Center" ValueChanged="ChangeMediaVolume" 
       Minimum="0" Maximum="1" Value="0.5" Width="70"/>

      <!-- Volume slider. This slider allows you to change the speed of the media playback. -->
      <TextBlock Foreground="White" Margin="5"  VerticalAlignment="Center">Speed</TextBlock>
      <Slider Name="speedRatioSlider" VerticalAlignment="Center" ValueChanged="ChangeMediaSpeedRatio" 
       Value="1" Width="70" />
      
      <!-- Seek to slider. Ths slider allows you to jump to different parts of the media playback. -->
      <TextBlock Foreground="White" Margin="5"  VerticalAlignment="Center">Seek To</TextBlock>
      <Slider Name="timelineSlider" Margin="5" ValueChanged="SeekToMediaPosition" Width="70"/>

    </StackPanel>
  </StackPanel>
</Page>

Implementare il controllo dell'interfaccia utente

Il codice seguente implementa la funzionalità dei controlli dell'interfaccia utente di esempio. I metodi Play, Pausee Stop vengono usati rispettivamente per riprodurre, sospendere e arrestare i media. Cambiare la proprietà Position di MediaElement consente di navigare nei contenuti multimediali. Infine, le proprietà Volume e SpeedRatio vengono usate per regolare il volume e la velocità di riproduzione dei media.

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Data;
using System.Windows.Media;
using System.Windows.Input;

namespace SDKSample
{

   public partial class MediaElementExample : Page
   {

      // Play the media.
      void OnMouseDownPlayMedia(object sender, MouseButtonEventArgs args)
      {

         // The Play method will begin the media if it is not currently active or
         // resume media if it is paused. This has no effect if the media is
         // already running.
         myMediaElement.Play();

         // Initialize the MediaElement property values.
         InitializePropertyValues();
      }

      // Pause the media.
      void OnMouseDownPauseMedia(object sender, MouseButtonEventArgs args)
      {

         // The Pause method pauses the media if it is currently running.
         // The Play method can be used to resume.
         myMediaElement.Pause();
      }

      // Stop the media.
      void OnMouseDownStopMedia(object sender, MouseButtonEventArgs args)
      {

         // The Stop method stops and resets the media to be played from
         // the beginning.
         myMediaElement.Stop();
      }

      // Change the volume of the media.
      private void ChangeMediaVolume(object sender, RoutedPropertyChangedEventArgs<double> args)
      {
         myMediaElement.Volume = (double)volumeSlider.Value;
      }

      // Change the speed of the media.
      private void ChangeMediaSpeedRatio(object sender, RoutedPropertyChangedEventArgs<double> args)
      {
         myMediaElement.SpeedRatio = (double)speedRatioSlider.Value;
      }

      // When the media opens, initialize the "Seek To" slider maximum value
      // to the total number of miliseconds in the length of the media clip.
      private void Element_MediaOpened(object sender, EventArgs e)
      {
         timelineSlider.Maximum = myMediaElement.NaturalDuration.TimeSpan.TotalMilliseconds;
      }

      // When the media playback is finished. Stop() the media to seek to media start.
      private void Element_MediaEnded(object sender, EventArgs e)
      {
         myMediaElement.Stop();
      }

      // Jump to different parts of the media (seek to).
      private void SeekToMediaPosition(object sender, RoutedPropertyChangedEventArgs<double> args)
      {
         int SliderValue = (int)timelineSlider.Value;

         // Overloaded constructor takes the arguments days, hours, minutes, seconds, milliseconds.
         // Create a TimeSpan with miliseconds equal to the slider value.
         TimeSpan ts = new TimeSpan(0, 0, 0, 0, SliderValue);
         myMediaElement.Position = ts;
      }

      void InitializePropertyValues()
      {
         // Set the media's starting Volume and SpeedRatio to the current value of the
         // their respective slider controls.
         myMediaElement.Volume = (double)volumeSlider.Value;
         myMediaElement.SpeedRatio = (double)speedRatioSlider.Value;
      }
   }
}

Imports System.Windows
Imports System.Windows.Controls
Imports System.Windows.Documents
Imports System.Windows.Navigation
Imports System.Windows.Shapes
Imports System.Windows.Data
Imports System.Windows.Media
Imports System.Windows.Input

Namespace SDKSample

    Partial Class MediaElementExample
        Inherits Page

        ' Play the media.
        Sub OnMouseDownPlayMedia(ByVal sender As Object, ByVal args As MouseButtonEventArgs)

            ' The Play method will begin the media if it is not currently active or 
            ' resume media if it is paused. This has no effect if the media is
            ' already running.
            myMediaElement.Play()

            ' Initialize the MediaElement property values.
            InitializePropertyValues()

        End Sub


        ' Pause the media.
        Sub OnMouseDownPauseMedia(ByVal sender As Object, ByVal args As MouseButtonEventArgs)

            ' The Pause method pauses the media if it is currently running.
            ' The Play method can be used to resume.
            myMediaElement.Pause()

        End Sub


        ' Stop the media.
        Sub OnMouseDownStopMedia(ByVal sender As Object, ByVal args As MouseButtonEventArgs)

            ' The Stop method stops and resets the media to be played from
            ' the beginning.
            myMediaElement.Stop()

        End Sub


        ' Change the volume of the media.
        Private Sub ChangeMediaVolume(ByVal sender As Object, ByVal args As RoutedPropertyChangedEventArgs(Of Double))
            myMediaElement.Volume = System.Convert.ToDouble(volumeSlider.Value)

        End Sub

        ' Change the speed of the media.
        Private Sub ChangeMediaSpeedRatio(ByVal sender As Object, ByVal args As RoutedPropertyChangedEventArgs(Of Double))
            myMediaElement.SpeedRatio = System.Convert.ToDouble(speedRatioSlider.Value)
            
        End Sub

        ' When the media opens, initialize the "Seek To" slider maximum value
        ' to the total number of miliseconds in the length of the media clip.
        Private Sub Element_MediaOpened(ByVal sender As Object, ByVal args As RoutedEventArgs)
            timelineSlider.Maximum = myMediaElement.NaturalDuration.TimeSpan.TotalMilliseconds
        End Sub

        ' When the media playback is finished. Stop() the media to seek to media start.
        Private Sub Element_MediaEnded(ByVal sender As Object, ByVal args As RoutedEventArgs)
            myMediaElement.Stop()
        End Sub

        ' Jump to different parts of the media (seek to). 
        Private Sub SeekToMediaPosition(ByVal sender As Object, ByVal args As RoutedPropertyChangedEventArgs(Of Double))
            Dim SliderValue As Integer = CType(timelineSlider.Value, Integer)

            ' Overloaded constructor takes the arguments days, hours, minutes, seconds, milliseconds.
            ' Create a TimeSpan with miliseconds equal to the slider value.
            Dim ts As New TimeSpan(0, 0, 0, 0, SliderValue)
            myMediaElement.Position = ts
        End Sub

        ' Set the media's starting Volume and SpeedRatio to the current value of the
        ' their respective slider controls.
        Private Sub InitializePropertyValues()
            myMediaElement.Volume = System.Convert.ToDouble(volumeSlider.Value)
            myMediaElement.SpeedRatio = System.Convert.ToDouble(speedRatioSlider.Value)
        End Sub
    End Class
End Namespace 'SDKSample

Vedere anche

• Controllare un oggetto MediaElement utilizzando lo storyboard