WPF Mediaelement LoadedBehavior 不能正常工作？

Question

我正在用 VB.NET 代码在 WPF 中创建一个简单的应用程序。此代码完美运行。选择文件后，函数returns根据媒体类型正确编号，当媒体是音频文件时出现音符图像，否则消失。媒体自动播放。但是我不需要自动播放媒体，当我将 LoadedBehavior 设置为手动（而不是默认播放）时，奇怪的事情发生了。 MediaOpened 事件会不时触发，函数 returns 有时为零，有时是正确的数字，有时是错误的数字。我在谷歌上搜索了将近三天，但一无所获。我想让 MediaElement.Play 和 MediaElement.Pause 显示 video/image 的第一帧，但如果没有将 LoadedBehavior 设置为手动，这是不可能的。我想以某种方式避免 LoadedBehavior。有人可以给我提示吗？非常感谢您。

Private Sub btnFile_Click(sender As Object, e As RoutedEventArgs) Handles btnFile.Click
        Try
            Me.MediaElementSetting.LoadedBehavior = MediaState.Manual
            Me.MediaElementSetting.UnloadedBehavior = MediaState.Close
            Me.MediaElementSetting.Stop()
            Me.MediaElementSetting.Close()
            Me.PvwTimer.Stop()
        Catch ex As Exception
            'The exception occurs when LoadedBehavior is not set to manual, that's why it's unused
            'MsgBox(ex.ToString)
        End Try
        Dim ArrayIndes as Integer = 1
        OpenFileDialog(ArrayIndex)
End Sub

Sub OpenFileDialog(ByVal ArrayIndex As Integer)
        Dim Dlg1 As New System.Windows.Forms.OpenFileDialog
        Dlg1.ShowDialog()
        If Dlg1.FileName <> "" Then
            strFile = Dlg1.FileName
            Me.MediaElementSetting.Source = New Uri(strFile, UriKind.RelativeOrAbsolute)
        End If
End Sub

Private Sub MediaElementSetting_MediaOpened(sender As Object, e As RoutedEventArgs) Handles MediaElementSetting.MediaOpened
        Dim t As Integer = AV()
End Sub

Function AV() As Integer
        'Check, if the media has timespan (if it is image, audio, video w sound, video w/o sound - image has video without timespan)
        If Me.MediaElementSetting.NaturalDuration.HasTimeSpan = True Then
            If Me.MediaElementSetting.HasAudio = True Then
                If Me.MediaElementSetting.HasVideo = True Then
                    'Media is a video with sound
                    MediaInfo = 4
                Else
                    'Media is an audio
                    MediaInfo = 2
                End If
            Else
                If Me.MediaElementSetting.HasVideo = True Then
                    'Media is a video without sound
                    MediaInfo = 3
                End If
            End If
        Else
            If Me.MediaElementSetting.HasVideo = True Then
                'Media is an image
                MediaInfo = 1
            End If
        End If

        If MediaInfo = 2 Then
            'Note is an image in a window. When the media is an audio it covers the mediaelement in a window
            Note.Visibility = Visibility.Visible
        Else
            Note.Visibility = Visibility.Hidden
        End If
        
        Return MediaInfo
    End Function

Answer 1

我不是 VB.NET 人，但这是 C# 中的一个工作示例。

这是 XAML。我有一个 MediaElement，一个 Border 作为笔记图像的 stand-in，还有一个按钮。

MainWindow.xaml

<Window x:Class="SO.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:SO"
    Title="MainWindow"
    Width="800"
    Height="450">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <MediaElement x:Name="MediaElementSetting"
            Margin="16" />
        <Border x:Name="AudioElement"
            Margin="16"
            Background="Red"
            Visibility="Collapsed">
            <TextBlock
                HorizontalAlignment="Center"
                VerticalAlignment="Center"
                Foreground="White"
                Text="AUDIO" />
        </Border>
        <Button x:Name="FileButton"
            Grid.Row="1"
            Margin="16"
            Padding="8,4"
            HorizontalAlignment="Right"
            VerticalAlignment="Bottom"
            Click="FileButton_OnClick"
            Content="File" />
    </Grid>
</Window>

这是 code-behind。

我在 window 的构造函数中初始化 MediaElement 一次。

为了显示视频的第一帧，我需要设置ScrubbingEnabled = true。

在 OpenFileDialog() 中，设置 Source 后我调用 SetupMedia，它立即调用 Play、Pause，然后设置 Position.这确保 MediaOpened 事件被调用。

在 OnMediaOpened 处理程序中，我调用 GetMediaInfo 就像您的 AV 函数，而不是 returning 一个整数，我 return改为枚举。

MainWindow.xaml.cs

using System;
using System.Diagnostics;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Forms;

namespace SO
{
    public partial class MainWindow : Window
    {
        private bool isMediaOpened;

        public MainWindow()
        {
            InitializeComponent();
            MediaElementSetting.LoadedBehavior = MediaState.Manual;
            MediaElementSetting.ScrubbingEnabled = true;
            MediaElementSetting.UnloadedBehavior = MediaState.Close;
            MediaElementSetting.MediaOpened += OnMediaOpened;
        }

        private void OnMediaOpened(object sender, RoutedEventArgs e)
        {
            isMediaOpened = true;
            var mediaInfo = GetMediaInfo();
            Debug.WriteLine($"{mediaInfo}");
        }

        private void SetupMedia()
        {
            MediaElementSetting.Play();
            MediaElementSetting.Pause();
            MediaElementSetting.Position = TimeSpan.FromSeconds(0);
        }

        private MediaInfo GetMediaInfo()
        {
            var mediaInfo = MediaInfo.None;

            if (MediaElementSetting.NaturalDuration.HasTimeSpan)
            {
                if (MediaElementSetting.HasAudio)
                {
                    mediaInfo = MediaElementSetting.HasVideo ? MediaInfo.VideoWithSound : MediaInfo.Audio;
                }
                else
                {
                    if (MediaElementSetting.HasVideo)
                    {
                        mediaInfo = MediaInfo.VideoNoSound;
                    }
                }
            }
            else
            {
                if (MediaElementSetting.HasVideo)
                {
                    mediaInfo = MediaInfo.Image;
                }
            }

            AudioElement.Visibility = mediaInfo == MediaInfo.Audio ? Visibility.Visible : Visibility.Collapsed;

            return mediaInfo;
        }

        private void FileButton_OnClick(object sender, RoutedEventArgs e)
        {
            OpenFileDialog();
        }

        private void OpenFileDialog()
        {
            var dialog = new OpenFileDialog();
            
            dialog.ShowDialog();

            if (!string.IsNullOrEmpty(dialog.FileName))
            {
                if (isMediaOpened)
                {
                    MediaElementSetting.Source = null;
                    isMediaOpened = false;
                }

                MediaElementSetting.Source = new Uri(dialog.FileName, UriKind.RelativeOrAbsolute);
                SetupMedia();
            }
        }

        public enum MediaInfo
        {
            None = 0,
            Image = 1,
            Audio = 2,
            VideoNoSound = 3,
            VideoWithSound = 4
        }
    }
}

Answer 2

好吧，我无意中找到了解决方案，非常适合我。 不要使用 MediaElement.LoadedBehavior = 完全不使用手册

Private Sub MediaElementSetting_MediaOpened(sender As Object, e As RoutedEventArgs) Handles MediaElementSetting.MediaOpened
    Dim t As Integer = AV()
    Me.MediaElementSetting.UnloadedBehavior = MediaState.Close
    Me.MediaElementSetting.LoadedBehavior = MediaState.Play
    Me.MediaElementSetting.LoadedBehavior = MediaState.Pause
End Sub

并使用 MediaElement.LoadedBehavior 控制媒体。这对我来说非常有效，即使我认为它不正确。从逻辑上讲，LoadedBehavior 表示加载的行为。

Sub PlayMedia()
    MediaElementSetting.LoadedBehavior = MediaState.Play
End Sub
Sub PauseMedia()
    MediaElementSetting.LoadedBehavior = MediaState.Pause
End Sub
Sub StopMedia()
    MediaElementSetting.LoadedBehavior = MediaState.Stop
End Sub

WPF Mediaelement LoadedBehavior 不能正常工作？

WPF Mediaelement LoadedBehavior does't work correctly?

vb.net

wpf

mediaelement