具有自动内存清理功能的图像下载器
本文关键字：功能 图像 下载 内存 | 更新日期: 2023-09-27 18:33:38
我有一个项目列表(简单的列表框(，其中包含主从基础上的图像(如果用户单击列表项，则会打开详细信息页面(。我遇到了非常著名的图像内存泄漏问题，在这里，这里，这里和这里描述。
一种可能的方法是在导航自时遍历所有图像并清理它们。
在其中一个线程中，我发现了更有趣的解决方案：它会自动清理图像，但这不适用于虚拟化(图像丢失或混合，如果要添加用于存储 ImageSource 的私有字段(。建议的解决方法是添加依赖项属性。
但我仍然面临同样的问题：向下滚动并向上返回后图像会混淆。看起来依赖属性是随机更改的，但我无法捕捉它们更改的时刻。
public class SafePicture : ContentControl
{
public static readonly DependencyProperty SafePathProperty =
DependencyProperty.RegisterAttached(
"SafePath",
typeof(string),
typeof(SafePicture),
new PropertyMetadata(OnSourceWithCustomRefererChanged));
public string SafePath
{
get { return (string)GetValue(SafePathProperty); }
set { SetValue(SafePathProperty, value); }
}
private static void OnSourceWithCustomRefererChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
{
if (e.NewValue == null) // New value here
return;
}
public SafePicture()
{
Content = new Image();
Loaded += OnLoaded;
Unloaded += OnUnloaded;
}
private void OnLoaded(object _sender, RoutedEventArgs _routedEventArgs)
{
var image = Content as Image;
if (image == null)
return;
var path = (string)GetValue(SafePathProperty); // Also, tried SafePath (debugger cant catch setter and getter calls), but same result.
image.Source = null;
{
var request = WebRequest.Create(path) as HttpWebRequest;
request.AllowReadStreamBuffering = true;
request.BeginGetResponse(result =>
{
try
{
Stream imageStream = request.EndGetResponse(result).GetResponseStream();
DispatcherHelper.CheckBeginInvokeOnUI(() =>
{
if (imageStream == null)
{
image.Source = new BitmapImage { UriSource = new Uri(path, UriKind.Relative) };
return;
}
var bitmapImage = new BitmapImage();
bitmapImage.CreateOptions = BitmapCreateOptions.BackgroundCreation;
bitmapImage.SetSource(imageStream);
image.Source = bitmapImage;
});
}
catch (WebException)
{
}
}, null);
}
}
private void OnUnloaded(object sender, RoutedEventArgs e)
{
var image = Content as Image;
if (image == null)
return;
var bitmapImage = image.Source as BitmapImage;
if (bitmapImage != null)
bitmapImage.UriSource = null;
image.Source = null;
}
}
用法：
<wpExtensions:SafePicture SafePath="{Binding ImageUrl}"/>
因此，乍一看，它工作正常，但是如果向下滚动并向上返回，图像会随机更改。
编辑：在这种情况下，目前，我只使用纯ListBox，没有虚拟化(但在其他情况下期望它(。
EDIT2：重现此问题的示例项目。我相信，它会在一段时间内包含解决方案：https://simca.codeplex.com/
问题是，在使用虚拟化时，用于每个项目的 ui 元素会被回收并重用于其他对象(因此包括图像对象(，并且由于您在滚动足够快时异步加载图像，您将在已经重用于另一个项目的图像上设置位图。
一个快速解决方法是检查路径值是否仍然相同，如果不是，只需返回，因为图像已被重新用于另一个对象：
...
var request = WebRequest.Create(path) as HttpWebRequest;
request.AllowReadStreamBuffering = true;
request.BeginGetResponse(result =>
{
try
{
Stream imageStream = request.EndGetResponse(result).GetResponseStream();
DispatcherHelper.CheckBeginInvokeOnUI(() =>
{
if (path!=SafePath){
//Item has been recycled
return;
}
....
编辑：代码中存在几个问题： -开关寄存器附加到寄存器，寄存器附加是用于附加属性而不是普通依赖属性 -调用 OnLoaded in OnSourceWithCustomRefererChanged 因为 SafePath 属性更改实际上可以在加载元素后 apppen - 在onLoaded的开头添加清除uri和源，以便在路径为空时清除图像
这是一个完整的工作代码：
public class SafeImage : ContentControl
{
private SynchronizationContext uiThread;
public static readonly DependencyProperty SafePathProperty =
DependencyProperty.Register("SafePath", typeof (string), typeof (SafeImage),
new PropertyMetadata(default(string), OnSourceWithCustomRefererChanged));
public string SafePath
{
get { return (string) GetValue(SafePathProperty); }
set { SetValue(SafePathProperty, value); }
}
private static void OnSourceWithCustomRefererChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
{
SafeImage safeImage = o as SafeImage;
safeImage.OnLoaded(null, null);
//OnLoaded(null, null);
if (e.NewValue == null)
return;
}
public SafeImage()
{
Content = new Image();
uiThread = SynchronizationContext.Current;
Loaded += OnLoaded;
Unloaded += OnUnloaded;
}
private void OnLoaded(object _sender, RoutedEventArgs _routedEventArgs)
{
var image = Content as Image;
if (image == null)
return;
var path = SafePath; //(string)GetValue(SafePathProperty);
//image.Source = new BitmapImage(new Uri(SafePath));
Debug.WriteLine(path);
var bitmapImage = image.Source as BitmapImage;
if (bitmapImage != null)
bitmapImage.UriSource = null;
image.Source = null;
if (String.IsNullOrEmpty(path))
{
//image.Source = new BitmapImage { UriSource = new Uri(Constants.RESOURCE_IMAGE_EMPTY_PRODUCT, UriKind.Relative) };
return;
}
// If local image, just load it (non-local images paths starts with "http")
if (path.StartsWith("/"))
{
image.Source = new BitmapImage { UriSource = new Uri(path, UriKind.Relative) };
return;
}
{
var request = WebRequest.Create(path) as HttpWebRequest;
request.AllowReadStreamBuffering = true;
request.BeginGetResponse(result =>
{
try
{
Stream imageStream = request.EndGetResponse(result).GetResponseStream();
uiThread.Post(_ =>
{
if (path != this.SafePath)
{
return;
}
if (imageStream == null)
{
image.Source = new BitmapImage { UriSource = new Uri(path, UriKind.Relative) };
return;
}
bitmapImage = new BitmapImage();
bitmapImage.CreateOptions = BitmapCreateOptions.BackgroundCreation;
bitmapImage.SetSource(imageStream);
image.Source = bitmapImage;
//imageCache.Add(path, bitmapImage);
}, null);
}
catch (WebException)
{
//uiThread.Post(_ =>
//{
// image.Source = new BitmapImage { UriSource = new Uri(Constants.RESOURCE_IMAGE_EMPTY_PRODUCT, UriKind.Relative) };
//}, null);
}
}, null);
}
}
private void OnUnloaded(object sender, RoutedEventArgs e)
{
var image = Content as Image;
if (image == null)
return;
var bitmapImage = image.Source as BitmapImage;
if (bitmapImage != null)
bitmapImage.UriSource = null;
image.Source = null;
}
}
最后要注意的是，Windows Phone ListBox默认使用虚拟化和回收(使用的ItemPanel是VirtualisedStackPanel(。