How to Isolate Silverlight Memory Leaks

Question

I have a memory leak in a silverlight app, I used this information to get started,

http://blogs.msdn.com/b/slperf/archive/2010/08/19/analyzing-silverlight-memory-usage-part-1-obtaining-measurements.aspx

Which was excellent. I have extracted some of my code to break down the issue. So the code looks like this, a child window,

<controls:ChildWindow x:Class="MemoryLeakTesting2.ConfirmDialog"
       xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
       xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
       xmlns:controls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls"
       xmlns:telerik="clr-namespace:Telerik.Windows.Controls;assembly=Telerik.Windows.Controls"        
       Width="375"   >
    <Grid Margin="2">
        <telerik:RadButton Content="OK" Click="OnClick" Command="{Binding CancelActionCommand}" Width="75" Height="23" HorizontalAlignment="Right" Margin="0,12,0,0" Grid.Row="1" />
    </Grid>
</controls:ChildWindow>

The code behind is this,

public partial class ConfirmDialog : ChildWindow
{
    public ConfirmDialog()
    {
        InitializeComponent();
    }

    [SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
    private void OnClick(object sender, RoutedEventArgs e)
    {
        DialogResult = true;
    }
}

I am calling this code from the button click event in my main silverlight page like this,

private void Button_Click(object sender, RoutedEventArgs e)
{
    ConfirmDialog dialog = new ConfirmDialog();
    dialog.Show();
}

This leaks memory every time I open the popup and close it. I use WinDbg and it actually shows that the ConfirmDialog instance is not freed after each time it is popped up and closed??

Answer 1

The Button.Command is notorious for leaking. My guess is that the value CancelActionCommand has a reference to a long lived object. The Button won't unhook from the ICommand.CanExecuteChanged event. You should consider using a Weak Event Pattern to limit your leakable surface area.

Here is a better explanation and example code to fix the problem.

Answer 2

Could it be:

On every click event you are creating ConfirmDialog object, which might hang around after it is no longer being used. Can you create that as a class variable and only have one reference and use that instead when you need to show the ChildWindow