设置mediaElement源的问题 [英] Problems with setting the source for mediaElement

问题描述

基本上我正在尝试创建一个简单的游戏，您将正在播放的歌曲与其所属的专辑封面相匹配。

我有一个类Song.vb只有属性

命名空间模型
 
公共类歌曲
 
公共财产标识As Integer 
 Public Property Title As String 
 Public Property Artist As String 
 Public Property Album As String 
 Public Property SongFile As StorageFile 
 Public Property Selected As Boolean 
公共属性用作布尔值
 
公共属性AlbumCover为BitmapImage 
 
 
结束类
 
结束命名空间

它会加载，拍照并开始游戏，问题是当声音应该播放时它会发挥作用，但事实并非如此。

我有这个StartCooldown函数准备新游戏，并调用我的CountDown故事板

 Private Sub StartCooldown（）
'启动我们的storyBoard for animation 
 _playingMusic = False 
 Dim brush As New SolidColorBrush（Colors.Blue）
 MyProgressBar.Foreground = brush 
 
 InstructionTextBlock.Text = String.Format（"准备好轮次{0} ..."，_round + 1） 
 InstructionTextBlock.Foreground =刷
 CountDown.Begin（）
 
 
结束子

和故事板Xaml

< Storyboard x：Name =" CountDown"完成= QUOT; CoolDown_Completed"> 
< DoubleAnimationUsingKeyFrames EnableDependentAnimation =" True" 
 Storyboard.TargetName =" MyProgressBar" 
 Storyboard.TargetProperty ="（RangeBase.Value）"> 
< DiscreteDoubleKeyFrame KeyTime =" 0"值= QUOT; 100" /> 
< DiscreteDoubleKeyFrame KeyTime =" 0：0：1"值= QUOT; 100" /> 
< DiscreteDoubleKeyFrame KeyTime =" 0：0：2"值= QUOT; 90" /> 
< DiscreteDoubleKeyFrame KeyTime =" 0：0：3"值= QUOT; 80 QUOT; /> 
< DiscreteDoubleKeyFrame KeyTime =" 0：0：4"值= QUOT; 70" /> 
< DiscreteDoubleKeyFrame KeyTime =" 0：0：5"值= QUOT; 60" /> 
< DiscreteDoubleKeyFrame KeyTime =" 0：0：6"值= QUOT; 50" /> 
< DiscreteDoubleKeyFrame KeyTime =" 0：0：7"值= QUOT; 40" /> 
< DiscreteDoubleKeyFrame KeyTime =" 0：0：8"值= QUOT; 30英寸; /> 
< DiscreteDoubleKeyFrame KeyTime =" 0：0：9"值= QUOT; 20" /> 
< DiscreteDoubleKeyFrame KeyTime =" 0：0：10"值= QUOT; 10" /> 
< / DoubleAnimationUsingKeyFrames>故事板执行后，
< / Storyboard> 

转到具有PickSong功能的CoolDown_Completed事件

 rivate Async Sub CoolDown_Completed（sender As Object，e As Object）
 
如果不是_playingMusic那么
 
'开始播放音乐
 Dim song = PickSong（）
 
 
 MyMediaElement.SetSource（等待song.SongFile.OpenAsync（FileAccessMode.Read），song.SongFile.ContentType）
'开始倒计时
 
 StartCountDown（）
 End if 
 End Sub 
 
 Private Function PickSong（）
 
 Dim random As New Random 
 Dim unusedSongs = Songs.Where（Function（p）p.Used = False）
 
 
 Dim randomNumber = random.Next（unusedSongs.Count）
 Dim randomSong = unusedSongs.ElementAt（randomNumber） 
 randomSong.Selected = True 
 
返回randomS ong 
 
结束函数

当我调试它时，它会在行中抛出异常

 MyMediaElement.SetSource（Await song.SongFile.OpenAsync（FileAccessMode.Read），song.SongFile.ContentType）

System.ArgumentNullException： '值不能为空。'

此部分代码的值：

等待song.SongFile.OpenAsync（FileAccessMode.Read）

是：  " {System._ComObject}"

并从此部分：

 song.SongFile.ContentType 

是：  " audio / mpeg"

我所有的歌曲文件都是mp3。

我的问题是，为什么我会得到空值异常，以及如何我可以播放我的歌吗？

解决方案

确保
MyMediaElement 不是Nothing。还要检查 song.SourceFile 的其他成员是否看起来不错。

使用一些显式存储文件尝试简化的
SetSource 。

Basicly i am trying to create a simple game where you match song that is playing to the album cover that it belongs to.

I have a class Song.vb that just has properties

Namespace Models

    Public Class Song

        Public Property Id As Integer
        Public Property Title As String
        Public Property Artist As String
        Public Property Album As String
        Public Property SongFile As StorageFile
        Public Property Selected As Boolean
        Public Property Used As Boolean

        Public Property AlbumCover As BitmapImage


    End Class

End Namespace

it loads, pictures, and starts the game, problem is when it comes to the part when the sound is supposed to be playing, it doesn't.

I have this StartCooldown Function that prepares for the new game, and calls my CountDown Storyboard

Private Sub StartCooldown()
        'starts our storyBoard for animation
        _playingMusic = False
        Dim brush As New SolidColorBrush(Colors.Blue)
        MyProgressBar.Foreground = brush

        InstructionTextBlock.Text = String.Format("Get ready for round {0} ...", _round + 1)
        InstructionTextBlock.Foreground = brush
        CountDown.Begin()


    End Sub

and the storyboard in Xaml

<Storyboard x:Name="CountDown" Completed="CoolDown_Completed">
            <DoubleAnimationUsingKeyFrames EnableDependentAnimation="True" 
                                           Storyboard.TargetName="MyProgressBar" 
                                           Storyboard.TargetProperty="(RangeBase.Value)">
                <DiscreteDoubleKeyFrame KeyTime="0" Value="100" />
                <DiscreteDoubleKeyFrame KeyTime="0:0:1" Value="100" />
                <DiscreteDoubleKeyFrame KeyTime="0:0:2" Value="90" />
                <DiscreteDoubleKeyFrame KeyTime="0:0:3" Value="80" />
                <DiscreteDoubleKeyFrame KeyTime="0:0:4" Value="70" />
                <DiscreteDoubleKeyFrame KeyTime="0:0:5" Value="60" />
                <DiscreteDoubleKeyFrame KeyTime="0:0:6" Value="50" />
                <DiscreteDoubleKeyFrame KeyTime="0:0:7" Value="40" />
                <DiscreteDoubleKeyFrame KeyTime="0:0:8" Value="30" />
                <DiscreteDoubleKeyFrame KeyTime="0:0:9" Value="20" />
                <DiscreteDoubleKeyFrame KeyTime="0:0:10" Value="10" />
            </DoubleAnimationUsingKeyFrames>
        </Storyboard>

after the storyboard executes it goes to CoolDown_Completed event that has PickSong function

rivate Async Sub CoolDown_Completed(sender As Object, e As Object)

        If Not _playingMusic Then

            'start playing music
            Dim song = PickSong()


            MyMediaElement.SetSource(Await song.SongFile.OpenAsync(FileAccessMode.Read), song.SongFile.ContentType)
            'start countdown 

            StartCountDown()
        End If
    End Sub

    Private Function PickSong()

        Dim random As New Random
        Dim unusedSongs = Songs.Where(Function(p) p.Used = False)


        Dim randomNumber = random.Next(unusedSongs.Count)
        Dim randomSong = unusedSongs.ElementAt(randomNumber)
        randomSong.Selected = True

        Return randomSong

    End Function

When i debugg it, it throws me an exception at line

MyMediaElement.SetSource(Await song.SongFile.OpenAsync(FileAccessMode.Read), song.SongFile.ContentType)

System.ArgumentNullException: 'Value cannot be null.'

The value of this part of code:

Await song.SongFile.OpenAsync(FileAccessMode.Read)

is:  "{System._ComObject}"

and from this part:

song.SongFile.ContentType

is :  "audio/mpeg"

All my song files are mp3.

My question is, why do i get the null value exception, and how can i get it to play my songs?

解决方案

Make sure that MyMediaElement is not Nothing. Also check if other members of song.SourceFile look good.

Try a simplified SetSource with some explicit storage file.

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