Silverlight2 边学边练 之四 音频播放器

众所周知Silverlight2对于音视频媒体也提供了很好的支持，本篇就音频部分做一个播放器实例。
本例实现的是播放器最基本的功能，大家可通过该例体会一下Silverlight2对音频的控制。
本例参考自《Pro Silverlight 2 in C# 2008》CHAPTER 10 SOUND, VIDEO, AND DEEP ZOOM

先上个效果图看看：

XAML Code：

<UserControl x:Class="MusicPlayer.Page"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Height="250" Width="200">
    <Grid Margin="20">
        <Grid.Background>
            <LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
                <GradientStop Color="Gold" Offset="0"></GradientStop>
                <GradientStop Color="White" Offset="0.5"></GradientStop>
                <GradientStop Color="Gold" Offset="1"></GradientStop>
            </LinearGradientBrush>
        </Grid.Background>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>
        </Grid.RowDefinitions>

        <!--媒体组件-->
        <MediaElement x:Name="media" AutoPlay="False" Source="test.mp3"  
                      MediaOpened="media_MediaOpened" 
                      MediaFailed="media_MediaFailed"
                      MediaEnded="media_MediaEnded" 
                      CurrentStateChanged="media_CurrentStateChanged">
        </MediaElement>
        <StackPanel Orientation="Horizontal">
            <!--播放键-->
            <Button Click="cmdPlay_Click" Padding="15" Margin="5">
                <StackPanel>
                    <Polygon Points="0,0 0,10 10,5" Fill="Green"></Polygon>
                </StackPanel>
            </Button>
            <!--停止键-->
            <Button Click="cmdStop_Click" Padding="15" Margin="5">
                <StackPanel>
                    <Rectangle Height="10" Width="10" Fill="Red"></Rectangle>
                </StackPanel>
            </Button>
            <!--暂停键-->
            <Button Click="cmdPause_Click" Padding="15" Margin="5">
                <StackPanel Orientation="Horizontal">
                    <Rectangle Margin="1" Height="10" Width="3" Fill="Blue"></Rectangle>
                    <Rectangle Margin="1" Height="10" Width="3" Fill="Blue"></Rectangle>
                </StackPanel>
            </Button>
        </StackPanel>

        <Grid Grid.Row="1" Margin="0,10,0,0">
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"></RowDefinition>
                <RowDefinition Height="Auto"></RowDefinition>
                <RowDefinition Height="Auto"></RowDefinition>
            </Grid.RowDefinitions>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto"></ColumnDefinition>
                <ColumnDefinition></ColumnDefinition>
            </Grid.ColumnDefinitions>

            <!--音量调节按钮-->
            <TextBlock Margin="5" Text="Volume: "></TextBlock>
            <Slider x:Name="sliderVolume" Grid.Column="1"  Minimum="0" Maximum="1" Value="0.5"
                    ValueChanged="sliderVolume_ValueChanged"></Slider>
            <!--平衡调节按钮-->
            <TextBlock Grid.Row="1" Margin="5" Text="Balance: "></TextBlock>
            <Slider x:Name="sliderBalance" Grid.Row="1" Grid.Column="1" Minimum="-1" Maximum="1"
                    ValueChanged="sliderBalance_ValueChanged"></Slider>
            <!--播放进度调节按钮-->
            <TextBlock Grid.Row="2" Margin="5" Text="Seek To: "></TextBlock>
            <Slider x:Name="sliderPosition" Minimum="0" Grid.Column="1" Grid.Row="2"
                    ValueChanged="sliderPosition_ValueChanged"></Slider>
            <!--播放进度条-->
            <Slider x:Name="sliderPositionBackground" Minimum="0" Grid.Column="1" Grid.Row="2" 
                    IsHitTestVisible="False" Opacity="0.5">
            </Slider>
        </Grid>

        <!--循环播放选项-->
        <CheckBox x:Name="chkLoop" Grid.Row="2" Margin="5,5,5,5" Content="Loop"></CheckBox>
        <!--静音选项-->
        <CheckBox x:Name="chkMute" Grid.Row="3" Margin="5,0" Content="Mute" Click="chkMute_Click"></CheckBox>
        <!--播放状态提示-->
        <TextBlock x:Name="lblStatus" Grid.Row="4" Margin="10" HorizontalAlignment="Center"></TextBlock>
    </Grid>
</UserControl>

C# Code：

using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Threading;

namespace MusicPlayer
{
    public partial class Page : UserControl
    {
        public Page()
        {
            InitializeComponent();
            //设置计时器精确度
            timer.Interval = TimeSpan.FromSeconds(0.1);
            //装载计时器
            timer.Tick += timer_Tick;
        }

        //停止播放
        public void mediaStop()
        {
            //将进度调节按钮与进度条归零
            sliderPosition.Value = 0;
            sliderPositionBackground.Value = 0;
            //停止播放
            media.Stop();
            timer.Stop();
        }

        private void timer_Tick(object sender, EventArgs e)
        {
            lblStatus.Text = media.Position.ToString().TrimEnd(new char[] { '0' });
            //使播放进度条跟随播放时间移动
            sliderPositionBackground.Value = media.Position.TotalSeconds;
        }

        //计时器
        private DispatcherTimer timer = new DispatcherTimer();

        //播放键
        private void cmdPlay_Click(object sender, RoutedEventArgs e)
        {
            //判断播放器是否处于暂停状态
            if (sliderPositionBackground.Value != 0)
            {
                //处于暂停状态则继续播放
                media.Position = TimeSpan.FromSeconds(sliderPositionBackground.Value);
                media.Play();
                timer.Start();
            }
            else
            {
                //处于停止状态则开始播放
                media.Stop();
                media.Play();
                timer.Start();
            }
        }

        //暂停键
        private void cmdPause_Click(object sender, RoutedEventArgs e)
        {
            media.Pause();
            timer.Stop();
        }

        //停止键
        private void cmdStop_Click(object sender, RoutedEventArgs e)
        {
            mediaStop();
        }
        
        //播放器打开
        private void media_MediaOpened(object sender, RoutedEventArgs e)
        {
            media.Stop();
            //将播放进度调节按钮和播放进度条的长度设为音频时长
            sliderPosition.Maximum = media.NaturalDuration.TimeSpan.TotalSeconds;
            sliderPositionBackground.Maximum = media.NaturalDuration.TimeSpan.TotalSeconds;
        }

        //播放进度调节按钮
        private void sliderPosition_ValueChanged(object sender, RoutedEventArgs e)
        {
            //使进度条跟随调节按钮移动
            sliderPositionBackground.Value = sliderPosition.Value;
            //从调节位置播放
            media.Stop();
            media.Position = TimeSpan.FromSeconds(sliderPosition.Value);
            media.Play();
            timer.Start();
        }

        //音量调节按钮
        private void sliderVolume_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
        {
            if (media != null) media.Volume = sliderVolume.Value;
        }

        //平衡调节按钮
        private void sliderBalance_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
        {
            media.Balance = sliderBalance.Value;
        }

        //静音选项
        private void chkMute_Click(object sender, RoutedEventArgs e)
        {
            media.IsMuted = (bool)chkMute.IsChecked;
        }

        //获取错误提示
        private void media_MediaFailed(object sender, ExceptionRoutedEventArgs e)
        {
            lblStatus.Text = e.ErrorException.Message;
        }

        //播放结束
        private void media_MediaEnded(object sender, RoutedEventArgs e)
        {
            //判断是否需要循环播放
            if ((bool)chkLoop.IsChecked)
            {
                //循环播放
                media.Position = TimeSpan.Zero;
                media.Play();
            }
            else
            {
                //停止播放
                mediaStop();
            }
        }

        //获取播放状态
        private void media_CurrentStateChanged(object sender, RoutedEventArgs e)
        {
            //在Textblock中显示播放状态
            lblStatus.Text = media.CurrentState.ToString();
        }
    }
}

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