Unmanaged leak in a trivial WPF application

问题:

I've run into a situation where I'm leaking unmanaged memory when the mouse is moved over my WPF app. Specifically, when I profile the application in perfmon or Red Gate's memory profiler, the private bytes monotonically increase, but the bytes in all managed heaps stay constant -- which, I believe, means that the app has an unmanaged leak.

I've created a trivial repro app, but I can't see where the problem is.

The app consists of a ListView with four items. Moving the mouse rapidly over these items causes the problem.

Here is the code if you're interested in reproducing the issue -- it's not pretty, but it's simple.

Thanks

---

edit: I've created a Microsoft Connect issue for this problem.

---

App.xaml

<Application x:Class="WpfLeakRepro.App"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    StartupUri="Window1.xaml">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="Generic.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>

App.xaml.cs

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Windows;

namespace WpfLeakRepro
{
    /// <summary>
    /// Interaction logic for App.xaml
    /// </summary>
    public partial class App : Application
    {
    }
}

Generic.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <LinearGradientBrush x:Key="ListItemHover"
                         EndPoint="0,1"
                         StartPoint="0,0">
        <GradientStop Color="Aqua"
                      Offset="0" />
        <GradientStop Color="White"
                      Offset="1" />
    </LinearGradientBrush>
    <LinearGradientBrush x:Key="ListItemSelected"
                         EndPoint="0,1"
                         StartPoint="0,0">
        <GradientStop Color="Blue"
                      Offset="0" />
        <GradientStop Color="White"
                      Offset="1" />
    </LinearGradientBrush>
    <VisualBrush x:Key="CheckeredBackground"
                 Viewport="20,20,20,20"
                 ViewportUnits="Absolute"
                 TileMode="Tile"
                 Stretch="Fill">
        <VisualBrush.Visual>
            <Canvas Opacity="5">
                <Rectangle Fill="#FF606060"
                           Height="21"
                           Width="21"
                           Canvas.Top="20" />
                <Rectangle Fill="#FF606060"
                           Width="21"
                           Height="21"
                           Canvas.Left="20" />
                <Rectangle Fill="#FF646464"
                           Height="21"
                           Width="21"
                           Canvas.Left="20"
                           Canvas.Top="20" />
                <Rectangle Fill="#FF646464"
                           Width="21"
                           Height="21" />
            </Canvas>
        </VisualBrush.Visual>
    </VisualBrush>
    <Style TargetType="{x:Type ListViewItem}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type ListViewItem}">
                    <Border Background="{TemplateBinding Background}">
                        <Grid>
                            <GridViewRowPresenter />
                        </Grid>
                    </Border>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsMouseOver"
                                 Value="true">
                            <Setter Property="Background"
                                    Value="{DynamicResource ListItemHover}" />
                        </Trigger>
                        <Trigger Property="IsSelected"
                                 Value="true">
                            <Setter Property="Background"
                                    Value="{DynamicResource ListItemSelected}" />
                        </Trigger>
                    </ControlTemplate.Triggers>

                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

Window1.xaml

<Window x:Class="WpfLeakRepro.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="449" Width="497">
    <Grid>
        <ListView Margin="12"
                  Name="listView"
                  ItemsSource="{Binding}">
            <ListView.View>
                <GridView>
                    <GridView.Columns>
                        <GridViewColumn Header="File Name">
                            <GridViewColumn.CellTemplate>
                                <DataTemplate>
                                    <TextBlock Text="{Binding Name}" />
                                </DataTemplate>
                            </GridViewColumn.CellTemplate>
                        </GridViewColumn>
                        <GridViewColumn Header="Thumbnail">
                            <GridViewColumn.CellTemplate>
                                <DataTemplate>
                                    <Border Background="{DynamicResource CheckeredBackground}" Width="72" Height=48/>
                                </DataTemplate>
                            </GridViewColumn.CellTemplate>
                        </GridViewColumn>
                    </GridView.Columns>
                </GridView>
            </ListView.View>
        </ListView>
    </Grid>
</Window>

Window1.xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.ComponentModel;
using System.Collections.ObjectModel;
using System.IO;

namespace WpfLeakRepro
{
    public class Picture
    {
        public string Name { get; set; }
    }

    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();

            List<Picture> pictures = new List<Picture>();

            string[] images = new string[] {"Blue hills.jpg", "Sunset.jpg", "Water lilies.jpg", "Winter.jpg" };

            foreach (string imagePath in images)
            {
                pictures.Add(new Picture() { Name = imagePath });
            }

            DataContext = pictures;
        }
    }
}

回答1:

You might have created a known memory leak in WPF Bindings that might occur when binding to properties of classes not implementing INotifyPropertyChanged. In your case the Name property of the Picture class.

Solutions are setting the binding Mode to OneTime, letting Picture implement INotifyPropertyChanged or making Name into a dependency property.

Read more about it from ms support and this blog post. These and other known WPF memory leaks can be found here.

回答2:

The issue appears to have something to do with the VisualBrush that was being used for the checkered background. Replace this with a SolidColorBrush, and the issue goes away. But it really doesn't matter: the folks at Microsoft suggested that I install the latest upgrades to .NetFx 3.5sp1, and this seems to fix the problem (more details here).