从绑定动态加载视频 [英] Dynamically Loading Video from Binding

问题描述

大家好

我正在尝试在MediaElement / VisualBrush中加载视频，如果我在Xaml中定义或直接从后面的代码中定义它，它就可以工作。如果我尝试相同的东西并通过绑定访问它，视频永远不会出现。

I am trying to load video in a MediaElement / VisualBrush and it works if I define it in Xaml or directly from the code behind. If I try the same thing and access it via a binding the video never shows up.

我已经在几个线程中读过freezable对象不是元素树的一部分因此无法绑定。

I have read in several threads that freezable objects are not part of the element tree and therefore cannot be bound.

有没有办法通过绑定动态加载视频（而不仅仅是更改源代码）。

Is there any way to dynamically load video via a binding (not just changing the source).

即使非常简单的例子，视频也不会出现。

Even really simple examples the video never shows up.

<Window
    x:Class="WpfApp1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfApp1"
    x:Name="MyWindow"
    Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <local:MainViewModel/>
    </Window.DataContext>
    <Grid x:Name="MyGrid" Background="{Binding MyBrush}">
    </Grid>
</Window>

和ViewModel

And the ViewModel

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

namespace WpfApp1
{
    class MainViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        protected void OnPropertyChanged(string name = "")
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
        }

        private VisualBrush myBrush = null;
        public VisualBrush MyBrush
        {
            get
            {
                return this.myBrush;
            }
            set
            {
                this.myBrush = value;
                OnPropertyChanged("MyBrush");
            }
        }

        public MainViewModel()
        {
            MediaElement myMediaElement = new MediaElement();
            myMediaElement.Source = new Uri("C:\\Work\\test.avi", UriKind.Absolute);
            myMediaElement.IsMuted = true;
            // myMediaElement.Loaded += Me_Loaded;

            VisualBrush myVisualBrush = new VisualBrush();
            myVisualBrush.Visual = myMediaElement;

            this.MyBrush = myVisualBrush;
        }

        private void Me_Loaded(object sender, RoutedEventArgs e)
        {
            MediaElement me = sender as MediaElement;
            if (me != null)
            {
                me.Play();
            }
        }
    }
}

推荐答案

你想在Uri中使用正斜杠你的viewmodel不应该对像MediaElement这样的UI元素有任何引用。

You want forward slashes in Uri and your viewmodel should not have any sort of a reference to a UI element like MediaElement.

这是我扔在一起的东西：

Here's something I threw together:

<Window x:Class="wpf_MediaElement_URL.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:wpf_MediaElement_URL"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <local:MainWindowViewModel/>
    </Window.DataContext>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="30"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

        <Button Content="Play" Command="{Binding PlayCommand}"/>
        <MediaElement Source="{Binding MeUri, NotifyOnTargetUpdated=True}"
                      TargetUpdated="MediaElement_TargetUpdated"
                      LoadedBehavior="Manual"
                      Grid.Row="1"/>
    </Grid>
</Window>

代码背后：

namespace wpf_MediaElement_URL
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void MediaElement_TargetUpdated(object sender, DataTransferEventArgs e)
        {
            MediaElement _me = e.TargetObject as MediaElement;
            if(_me.Source !=null)
            {
                _me.Play();
            }
        }
    }
}

Viewmodel

Viewmodel

using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.CommandWpf;

namespace wpf_MediaElement_URL
{
    public class MainWindowViewModel : ViewModelBase
    {
        private Uri meUri;

        public Uri MeUri
        {
            get { return meUri; }
            set { meUri = value; RaisePropertyChanged(); }
        }
        private RelayCommand _playCommand;

        public RelayCommand PlayCommand
        {
            get
            {
                return _playCommand
                ?? (_playCommand = new RelayCommand(
                () =>
                {
                    MeUri = new Uri(@"C://Code/wpf_MediaElement/wpf_MediaElement/bin/Debug/Bootstrap.wmv", UriKind.Absolute);
                }));
            }
        }
    }
}

vid来自我的另一个代码示例。

The vid is from another sample piece of code I had.

请注意，当源绑定更改时播放视频是一个视图责任，因此后面的代码不会破坏mvvvm。

Note that playing a video when the source binding changes is a view responsibility so the code behind doesn't break with mvvvm.

如果你有一大堆媒体元素您可以将其更改为resourcedictionary中的样式，并使用eventsetter设置事件处理程序。

If you had a load of mediaelements you could change that into a style in a resourcedictionary and have an eventsetter to set up the event handler.

这篇关于从绑定动态加载视频的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！