Question

My Application’s designed by MVVM.

Main window is MainWindow.xaml as below. Main Window has two usercontrols.

By the way, usercontrol is created dynamically in run-time, when property of viewmodel is changed.
But it seems my application has memory leak.

MainWindow.xaml

<Window x:Class="InstanceTest.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:InstanceTest"
    Title="MainWindow" Height="350" Width="525">
<Window.Resources>
    <local:MainWindowViewModel x:Key="MainWindowViewModel" />

    <DataTemplate x:Key="UD1">
        <ContentControl>
            <local:UserControl1></local:UserControl1>
        </ContentControl>
    </DataTemplate>

    <DataTemplate x:Key="UD2">
        <ContentControl>
            <local:UserControl2></local:UserControl2>
        </ContentControl>
    </DataTemplate>

    <DataTemplate x:Key="contentsTemplate">
        <ContentControl>
            <ContentControl.Style>
                <Style TargetType="ContentControl">
                    <Style.Triggers>
                        <DataTrigger Binding="{Binding ViewType}" Value="1">
                            <Setter Property="ContentTemplate" Value="{DynamicResource UD1}" />
                        </DataTrigger>

                        <DataTrigger Binding="{Binding ViewType}" Value="2">
                            <Setter Property="ContentTemplate" Value="{DynamicResource UD2}" />
                        </DataTrigger>

                    </Style.Triggers>
                </Style>
            </ContentControl.Style>
        </ContentControl>
    </DataTemplate>
</Window.Resources>
<Grid DataContext="{StaticResource MainWindowViewModel}">
    <StackPanel>
        <Button Height="30" Command="{Binding ChangeViewCommand}">ChangeView</Button>
        <ContentControl Content="{Binding}" ContentTemplate="{StaticResource contentsTemplate}" />
    </StackPanel>
</Grid>

MainWindow.xaml is related to MainWindowViewModel.cs.
According to ViewType property, each usercontrol is created dynamically in run time.

public class MainWindowViewModel : ViewModelBase
{

    private string viewType;
    public string ViewType
    {
        get { return viewType; }
        set 
        {
            viewType = value;
            base.RaisePropertyChanged(() => this.ViewType);
        }
    }

    public MainWindowViewModel()
    {
        ChangeViewCommand = new RelayCommand(ChangeView);
    }

    public ICommand ChangeViewCommand { get; private set; }
    private void ChangeView(object o)
    {
        int aa = 1000;
        while (aa > 0)
        {
            System.Threading.Thread.Sleep(1000);

            System.Windows.Forms.Application.DoEvents();

            if (ViewType == "1")
                ViewType = "2";
            else
                ViewType = "1";
            aa--;

            //GC.Collect();
        }
    }
}

UserControl1.xaml

 <UserControl.Resources>
    <local:uc1ViewModel x:Key="uc1ViewModel" />
</UserControl.Resources>
<Grid DataContext="{StaticResource uc1ViewModel}">
    <StackPanel>
        <TextBlock FontSize="30" Text="{Binding TextExample}"></TextBlock>
        <Image Source="/InstanceTest;component/Images/sample.jpg" />
    </StackPanel>
</Grid>

UserControl1.xaml has uc1ViewModel.cs. UserControl2.xaml has uc2ViewModel.cs as below.

public class uc1ViewModel : ViewModelBase
{
    private string textExample;
    public string TextExample
    {
        get { return textExample; }
        set
        {
            textExample = value;
            base.RaisePropertyChanged(() => this.TextExample);
        }
    }

    public uc1ViewModel()
    {
        TextExample = "UD1...";
    }

    ~uc1ViewModel()
    {
        Debug.WriteLine("Call Destructor");
    }

}

ChangeView Function of MainViewModel.cs changes ViewType property every second.
When changing property of ViewType, ui1ViewModel is created as new instance. If ui1ViewModel’s instance is created for the next time, I expect old instance of ui1ViewModel is removed by garbage collector.

But, it looks like application has memory leak when testing for bunch of times.
I checked destructor of ui1ViewModel
and type Debug.WriteLine(“Call Destructor”) at destructor. but it dosen’t call every times.
When I call GC.Collect() by force, destructor of ui1ViewModel is called and reduce memory size of application.

So, my question is

Can I call GC.collect() by force in this case? or do you have other way to solve this problem?

Answer 1

I don’t think it is a memory leak either:

A correctly-written program cannot assume that finalizers will ever
run.

Raymond Chen has a nice explanation on what people wrongly understand by Garbage Collection:
http://blogs.msdn.com/b/oldnewthing/archive/2010/08/09/10047586.aspx

I’ll always remember this:

Garbage collection is simulating a computer with an infinite amount of
memory. The rest is mechanism.