WPF not releasing memory

Question

I have a issue in our application where the memory is not released when the user controls are unloaded. This will increase the memory starting from 40MB and ends up with 200MB and more.

To simulate this,

1. I created a wpf project which has the main window and a user control
2. loaded 1000 objects into a wpf datagrid which is placed in a user control
3. A scroll viewer is put in the main window
4. The user control is loaded inside this scroll viewer Once the show button is clicked
5. The user control is removed from the Content of the Scroll viwer once the Close button is clicked

Once i checked with the task manager, before the 1000 objects are loaded to the grid, the memory consumption is 14MB. Once its loaded by clicking on the show button it increases to 70MB. But when i click on Close button to remove the user control from the window, the memory reduces to 67MB only. Shouldn't it reduce to 14BMB or something close to that??

When i checked this with the ANTS memory profiler, it shows that the 1000 objects remain in memory even after the User control is removed from the Window. Shouldn't the garbage collector release these objects when the user control is removed from the window (once the Scroll viewer Content Property is set to null)?

Following is the Code i used for this. I didn't use any styles, data templates or any third party controls, only used the WPF DataGrid control to load the data.

The User Control Code Behind

public partial class UserControl1 : UserControl,IDisposable
{
    List<TestClass> list = null;

    public UserControl1()
    {
        InitializeComponent();
    }

    public void Dispose()
    {
        BindingOperations.ClearBinding(dgList, DataGrid.ItemsSourceProperty);
        list.Clear();
        GC.Collect();
    }

    private void UserControl_Loaded(object sender, RoutedEventArgs e)
    {
        list = new List<TestClass>();

        for (int i = 0; i < 1000; i++)
        {
            TestClass obj = new TestClass();
            obj.Name = "test name";
            obj.Age = 34;

            list.Add(obj);
        }
        dgList.ItemsSource = list;
    }

}

public class TestClass
{
    public string Name { get; set; }
    public int Age { get; set; }     
}

Main Window Code behind

public partial class MainWindow : Window
{
    UserControl1 control = null;

    public MainWindow()
    {
        InitializeComponent();
    }

    private void btnClose_Click(object sender, RoutedEventArgs e)
    {
        control.Dispose();
        scwContent.Content = null;
        control = null;

    }

    private void btnShow_Click(object sender, RoutedEventArgs e)
    {
        control = new UserControl1();
        scwContent.Content = control;
    }
}

Thanks.

Answer 1

Why are you trying to call GC? That is not required

Change

for (int i = 0; i < 1000; i++)        
{            
    TestClass obj = new TestClass();
    ...

To

TestClass obj;
for (int i = 0; i < 1000; i++)       
{         
     obj = new TestClass();
     ...

You can set the list object to null .. Read this for understanding setting objects to null Setting an object to null vs Dispose()

Answer 2

The Garbage collector only collects when memory is needed, not when references are set to null.

(Only exception: calling GC.Collect())