WPF 无法更新窗口元素

DispatcherTimer在窗口代码内部使用了一个滑块。但是在转移到控制图片缓存和更改幻灯片的单独的单例线程类之后，会弹出一个错误。

帮助克服将图像传输到表单时发生的此错误。我不明白我做错了什么。就像通过委托发布对窗口的访问一样。和类似的结构一样，可以正常使用表单的文本字段，但不存在图像。

MainWindow.xaml.cs 代码：

public partial class MainWindow : Window
{
    private delegate void slideCacheUpdateDelegate(int slide, BitmapImage image);

    public MainWindow()
    {
        SlideCache.getInstance.init();

        InitializeComponent();

        // Initial slide cache updater delegate.
        SlideCache.OnRefresh += (s, i) =>
        {
            if (Dispatcher.CheckAccess())
                changeToNextSlide(s, i);
            else
                Dispatcher.BeginInvoke(new slideCacheUpdateDelegate(changeToNextSlide), new object[] { s, i });
        };

        SlideCache.getInstance.startSlideShow();
    }

    private void changeToNextSlide(int slide, BitmapImage image)
    {
        switch (slide)
        {
            case 1:
                this.imageSlide2.Source = image;
                DoubleAnimation animationSlide1 = new DoubleAnimation();
                animationSlide1.From = 0;
                animationSlide1.To = 1;
                animationSlide1.Duration = TimeSpan.FromMilliseconds(500);
                this.imageSlide2.BeginAnimation(Canvas.OpacityProperty, animationSlide1);
                break;

            case 2:
                this.imageSlide1.Source = image;
                DoubleAnimation animationSlide2 = new DoubleAnimation();
                animationSlide2.From = 1;
                animationSlide2.To = 0;
                animationSlide2.Duration = TimeSpan.FromMilliseconds(500);
                this.imageSlide2.BeginAnimation(Canvas.OpacityProperty, animationSlide2);
                break;
        }
    }
}

MainWindow.xaml 代码：

<Window x:Class="SlideShow.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <StackPanel Width="200" Height="100" Background="Black">
            <Image Name="imageSlide1" Stretch="Fill"/>
            <Image Name="imageSlide2" Stretch="Fill"/>
        </StackPanel>
    </Grid>
</Window>

SlideCache.cs 代码：

public class SlideCache
{
    public delegate void Slider(int slide, BitmapImage holder);
    public static event Slider OnRefresh;

    private static volatile SlideCache INSTANCE;
    private static object syncRoot = new Object();

    private Thread _threadCache;
    private Thread _threadSlide;

    private Dictionary<int, BitmapHolder> _images;

    private int _currentSlide;

    private Boolean _isFirstImage;

    private SlideCache()
    {
        // Do nothing.
    }

    public void init()
    {
        initDictionary();

        _currentSlide = 0;
        _isFirstImage = true;

        _threadCache = new Thread(slideCache);
        _threadCache.IsBackground = true;
        _threadCache.SetApartmentState(ApartmentState.MTA);
        _threadCache.Start();
    }

    private void slideShow()
    {
        while (true)
        {
            ++_currentSlide;
            if (_images[_currentSlide] != null)
            {
                slideUpdate(_isFirstImage ? 1 : 2, _images[_currentSlide].getImage());
                _isFirstImage = !_isFirstImage;
            }

            Thread.Sleep(3000);
        }
    }

    private void slideCache()
    {
        while (true)
        {
            DateTime timestamp = DateTime.Now;
            for (int i = 0; i < 10; i++ )
            {
                int slideId = i + 1;
                BitmapHolder holder = _images[slideId];
                if (holder == null || holder.getTimestamp() < timestamp)
                {
                    BitmapImage image = new BitmapImage();
                    image.BeginInit();
                    image.UriSource = new Uri("http://example.com/slide_" + slideId);
                    image.EndInit();

                    if (holder != null && holder.getImage() != null && image.PixelWidth == 1)
                        continue;

                    _images[slideId] = new BitmapHolder(timestamp.AddSeconds(new Random().Next(180, 600)), image);
                }
            }

            Thread.Sleep(1000);
        }
    }

    private void initDictionary()
    {
        _images = new Dictionary<int, BitmapHolder>(10);

        for (int i = 0; i < 10; i++)
            _images.Add((i + 1), null);
    }

    private void slideUpdate(int slide, BitmapImage image)
    {
        OnRefresh.Invoke(slide, image);
    }

    public void startSlideShow()
    {
        _threadSlide = new Thread(slideShow);
        _threadSlide.IsBackground = true;
        _threadSlide.SetApartmentState(ApartmentState.MTA);
        _threadSlide.Start();
    }

    public void stopSlideShow()
    {
        _threadSlide.Abort();
    }

    public void changeToNextSlide(int slide)
    {
        _currentSlide = slide;
        slideUpdate(_isFirstImage ? 1 : 2, _images[_currentSlide].getImage());
        _isFirstImage = !_isFirstImage;
    }

    public Boolean slideShowEnabled()
    {
        return _threadSlide.ThreadState == ThreadState.Running;
    }

    public static SlideCache getInstance
    {
        get
        {
            if (INSTANCE == null)
            {
                lock (syncRoot)
                {
                    if (INSTANCE == null)
                        INSTANCE = new SlideCache();
                }
            }

            return INSTANCE;
        }
    }
}

BitmapHolder.cs 代码：

public class BitmapHolder
{
    private DateTime _timestamp;
    private BitmapImage _image;

    public BitmapHolder(DateTime timestamp, BitmapImage image)
    {
        _timestamp = timestamp;
        _image = image;
    }

    public DateTime getTimestamp()
    {
        return _timestamp;
    }

    public BitmapImage getImage()
    {
        return _image;
    }
}

启动应用程序时卡住并在VS中弹出以下错误：

用户代码未处理 System.InvalidOperationException调用线程无法访问此对象，因为另一个线程拥有此对象。

解决方案：

BitmapImage image = new BitmapImage();
image.BeginInit();
image.CacheOption = BitmapCacheOption.OnLoad;
image.StreamSource = new MemoryStream(new WebClient().DownloadData("http://example.com/Slide_" + slideId + ".png"));
image.EndInit();
image.Freeze();

感谢MSDN.WhiteKnight帮助我查看本地资源。您的回答最接近解决问题。

PS 问题本身不是从另一个线程访问 UI 元素，而是来自Singleton类的线程试图转移到 UI 的阻塞资源。那些。有必要将图片作为流并基于它创建资源。进一步如 MSDN 中的Freeze()共享描述。我希望它对某人有用，tk。问题不是孤立的，至少在 EN SO 是这样。