小编典典

当列表框中有图像时,为什么会出现OutOfMemoryException?

c#

我想在我的自定义库中ListBox显示Windows Phone 8照片文件夹中存储的所有图像,该文件夹用于显示图像。

ListBox代码如下:

    <phone:PhoneApplicationPage.Resources>
        <MyApp:PreviewPictureConverter x:Key="PreviewPictureConverter" />
    </phone:PhoneApplicationPage.Resources>

    <ListBox Name="previewImageListbox" VirtualizingStackPanel.VirtualizationMode="Recycling">
        <ListBox.ItemsPanel>
            <ItemsPanelTemplate>
                <VirtualizingStackPanel CleanUpVirtualizedItemEvent="VirtualizingStackPanel_CleanUpVirtualizedItemEvent_1">
                </VirtualizingStackPanel>
            </ItemsPanelTemplate>
        </ListBox.ItemsPanel>
        <ListBox.ItemTemplate>
            <DataTemplate>
                <Grid>
                    <Image Source="{Binding Converter={StaticResource PreviewPictureConverter}}" HorizontalAlignment="Center" VerticalAlignment="Center" />
                </Grid>
            </DataTemplate>
        </ListBox.ItemTemplate>
     </ListBox>

使用以下转换器:

public class PreviewPictureConverter : System.Windows.Data.IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        PreviewImageItem c = value as PreviewImageItem;
        if (c == null)
            return null;
        return c.ImageData;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

图像存储在自定义类中:

class PreviewImageItem
{
    public Picture _picture = null;
    public BitmapImage _bitmap = null;

    public PreviewImageItem(Picture pic)
    {
        _picture = pic;
    }

    public BitmapImage ImageData 
    {
        get
        {
            System.Diagnostics.Debug.WriteLine("Get picture " + _picture.ToString());
            _bitmap = new BitmapImage();
            Stream data = _picture.GetImage();
            try
            {
                _bitmap.SetSource(data); // Out-of memory exception (see text)
            }
            catch (Exception ex)
            {
                System.Diagnostics.Debug.WriteLine("Exception : " + ex.ToString());
            }
            finally
            {
                data.Close();
                data.Dispose();
                data = null;
            }

            return _bitmap;
        }
    }
}

以下代码用于设置ListBox数据源:

private List<PreviewImageItem> _galleryImages = new List<PreviewImageItem>();

using (MediaLibrary library = new MediaLibrary())
{
    PictureCollection galleryPics = library.Pictures;
    foreach (Picture pic in galleryPics)
    {
        _galleryImages.Add(new PreviewImageItem(pic));
    }

    previewImageListbox.ItemsSource = _galleryImages;
};

最后是“清理”代码:

private void VirtualizingStackPanel_CleanUpVirtualizedItemEvent_1(object sender, CleanUpVirtualizedItemEventArgs e)
{
    PreviewImageItem item = e.Value as PreviewImageItem;

    if (item != null)
    {
        System.Diagnostics.Debug.WriteLine("Cleanup");
        item._bitmap = null;
    }
}

所有这些都可以正常工作,但是代码OutOfMemoryException在显示几张图像后崩溃(特别是在快速滚动时)。滚动VirtualizingStackPanel_CleanUpVirtualizedItemEvent_1时,该方法称为常规(例如,每2或3个列表框条目)ListBox

此示例代码有什么问题?

为什么没有释放内存(足够快)?


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2020-05-19

共1个答案

小编典典

哦,最近我整天杀了这个,使它正常工作!

因此解决方案是:

使您的图像控件免费资源。所以设置

BitmapImage bitmapImage = image.Source as BitmapImage;
bitmapImage.UriSource = null;
image.Source = null;

如前所述。

确保在列表的每个项目上虚拟化_bitmap。您应该按需加载它(LongListSelector.Realized方法),并且必须销毁它!它不会自动收集,并且GC.Collect也不能工作。空引用也不起作用:(但是这里是方法:制作1x1像素文件。将其复制到程序集中并从中获取资源流以处置1x1像素为空白的图像。将自定义处置方法绑定到LongListSelector.UnRealized事件(e。容器处理您的列表项)。

public static void DisposeImage(BitmapImage image)
{
    Uri uri= new Uri("oneXone.png", UriKind.Relative);
    StreamResourceInfo sr=Application.GetResourceStream(uri);
    try
    {
        using (Stream stream=sr.Stream)
        {
            image.DecodePixelWidth=1; //This is essential!
            image.SetSource(stream);
        }
    }
    catch { }
}

在LongListSelector中为我工作,每个图像有1000张宽度为400的图片。

如果您错过了数据收集的第2步,则可以看到良好的结果,但是在滚动100-200个项目后内存溢出。

2020-05-19