消除引用后,XAML按钮不会被垃圾回收

Question

我写了一个测试程序,其中单个Button在XAML中定义为a的内容Window.在窗口加载时,以Button编程方式替换为窗口的内容,并且引用它的字段也由Button我以编程方式创建的另一个字段替换.之后我Button使用弱引用跟踪两个对象,并以1/10秒的间隔轮询IsAlive每个对象的属性.在第IsAlive一次调用轮询方法的第一次检查之前,我也删除了以编程方式定义的生根引用Button.

运行此代码的期望是,尽管C#垃圾收集的时间不确定,但两个Button对象最终都会被报告为垃圾收集.尽管以编程方式定义Button了这种行为,通常在1/2分钟内,但从Button不收集XAML .看到这种行为,我已经让程序运行了十多分钟.

谁能告诉我为什么Button没有收集XAML 对象？特别是,我想知道垃圾收集阻止引用的位置,它是在我的代码中还是在WPF实现中.也许它在XAML加载对象中.我在看某种内存泄漏吗？

上面描述的程序包括在下面以供参考.

MainWindow.xaml:

<Window x:Class="Test.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Width="300" Height="150" Loaded="Window_Loaded">
    <Button Name="btn" />
</Window>

MainWindow.xaml.cs:

namespace Test {
    public partial class MainWindow : System.Windows.Window {

        private System.WeakReference wr_xamlBtn, wr_programmaticBtn;

        public MainWindow() {
            InitializeComponent();
        }

        private void Window_Loaded(object sender, System.Windows.RoutedEventArgs e) {

            // Immediately upon the window's loading, create a weak reference to the
            //  button %btn defined in XAML.
            wr_xamlBtn = new System.WeakReference(btn);

            // Replace references in %btn and this.Content to the XAML button with
            //  references to a programmatically-defined button. This would be
            //  expected to free the XAML button for garbage collection.
            btn = new System.Windows.Controls.Button();
            Content = btn;

            // Create a weak reference to the programmatically-defined button, so that
            //  when (strong) references to it are removed, it will be eligible for
            //  garbage collection.
            wr_programmaticBtn = new System.WeakReference(btn);

            // Provides a polling mechanism to see whether either the XAML button or
            //  the programmatically-defined button has been collected.
            var dt = new System.Windows.Threading.DispatcherTimer();
            dt.Tick += Poll;
            dt.Interval = System.TimeSpan.FromMilliseconds(100);
            dt.Start();
        }

        void Poll(object sender, System.EventArgs e) {

            // If the programmatically-defined button hasn't had its references
            //  removed yet, this does so. This makes it eligible for garbage
            //  collection.
            if (btn != null)
                Content = btn = null;

            // Uses the console to show a timestamp and the state of collection of the
            //  XAML button and the programmatically-defined button.
            System.Console.WriteLine(
                string.Format(
                    "XAML button {0}, Programmatically-defined button {1} @ {2}",
                    wr_xamlBtn.IsAlive ? "Alive" : "Collected",
                    wr_programmaticBtn.IsAlive ? "Alive" : "Collected",
                    System.DateTimeOffset.Now));
        }
    }
}

App.xaml:

<Application x:Class="Test.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             StartupUri="MainWindow.xaml" />

Answer 1

该按钮未被收集，因为它在 Window 名称范围内被强烈引用：

但它不应该被识别为内存泄漏，因为您应该在范围内重新注册新按钮：

//...
INameScope scope = NameScope.GetNameScope(this);
scope.UnregisterName("btn");
btn = new System.Windows.Controls.Button();
Content = btn;
scope.RegisterName("btn", btn);
//...