BUG:WP8命令绑定内存泄漏 [英] BUG: WP8 Command binding memory leak

问题描述

命令绑定可防止对控件进行GC.

我尝试了SL4，WPF，WP8，看来这只是WP8错误\行为.

示例应用程序已上传到我的skydrive文件夹中:https://skydrive.live.com/?cid=c6bca5f19c01f4f7&id=C6BCA5F19C01F4F7%214744

简而言之:您需要3件事来对其进行复制:
1)VirtualizingStackPanel.VirtualizationMode ＝标准".在列表上，因此它可以重新创建容器，而不是重复使用它们.
2)Command ="{Binding TestCommand}"；在DataTemplate中的任何按钮内
3)在按钮旁边的同一数据模板中的UserControl，带有一些专用字节数组，可以像镜像一样模拟大量内存的使用.同时在输出日志中放置一个终结器，以查看它直到OOM才真正被调用.

解决方案

Mutari，

非常感谢您举报此事.这似乎是一个已知问题，已记录到我们的问题数据库中.这是Silverlight特有的问题，我希望在将来的操作系统更新中可以修复此问题.

将命令对象绑定到命令"时， ButtonBase的属性，将ButtonBase注册到命令对象的CanExecuteChanged事件.这将创建对对象实例的强引用.

然后，如果可视树发生变化(例如，通过在ContentControl中加载新的DataTemplate)，则该按钮当然不会被垃圾收集，甚至会阻止所有父控件也被垃圾收集. /p>

正确的行为应该是使用"WeakEventListener"就像一个ItemsControl一样，它监听一个集合的更改事件.

您可以通过遵循以下Silverlight线程中描述的模式(在WeakEventSource中搜索线程)来实现变通方法:

命令绑定内存泄漏

希望这会有所帮助，
标记

Command binding prevents a control from being GCed.

I tried SL4, WPF, WP8 and it seems this is only WP8 bug\behavior.

Example app is uploaded to my skydrive folder: https://skydrive.live.com/?cid=c6bca5f19c01f4f7&id=C6BCA5F19C01F4F7%214744

In short: you need 3 things to repro it:
1) VirtualizingStackPanel.VirtualizationMode="Standard" on a list, so it recreates containers instead of reusing them.
2) Command="{Binding TestCommand}" inside any button in DataTemplate
3) A UserControl in the same data template next to the button, with some private byte array to emulate heavy memory usage like images do. Also put a finalizer there with output logging to see it never actually be called until OOM.

解决方案

Hi Mutari,

Thank you very much for reporting this. This appears to be a known issue that has been logged into our issues database. It is a Silverlight specific issue and I would anticipate that a fix will be rolled into a future OS update.

When a command object is bound to the "Command" property of a ButtonBase, the ButtonBase registers to the CanExecuteChanged event of the command object. This creates a strong reference to the object instance.

Then, if the visual tree changes (for example, by loading a new DataTemplate in a ContentControl), the button is, of course, not garbage collected, and will even prevent all the parent controls from being garbage collected also.

The correct behavior should be to use a "WeakEventListener" like an ItemsControl listening to the change events of a collection.

You can implement the workaround by following the pattern described in the following Silverlight thread (search the thread for WeakEventSource):

Command Binding Memory Leak

Hope this helps,
Mark

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