Question

我编写了一个测试程序，其中在XAML中将单个Button定义为Window的内容。在窗口加载时，Button以编程方式替换为窗口的内容，并且引用它的字段也被我以编程方式创建的另一个Button替换。此后，我使用弱引用跟踪两个Button对象，并以1/10秒的间隔轮询每个IsAlive属性。在第一次调用轮询方法时第一次检查IsAlive之前，我也删除了对编程定义的Button的生根引用。

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

有谁能告诉我为什么XAML Button对象没有被收集？ 特别是，我想知道垃圾收集阻止引用的位置，无论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？

上述程序包含在下面以供参考。

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：

MemProfiler snapshot

但它不应被视为内存泄漏，因为应该在范围内重新注册您的新按钮：

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

消除引用后，XAML按钮不会被垃圾回收

1 个答案: