Commits on Jul 13, 2023

1. [controls] fix memory leak with Grid Row/ColumnDefinitions …

   Context: dotnet#15860
   
   In a customer's app, they have the setup:
   
       <!-- Resources/Styles/Styles.xaml -->
       <Style TargetType="Grid" x:Key="GridStyleWithColumnDefinitions">
           <Setter Property="ColumnDefinitions" Value="18,*"/>
       </Style>
   
   Then a page with:
   
       <Grid Style="{StaticResource GridStyleWithColumnDefinitions}" />
   
   Navigating forward & back from this page would show that the entire
   `Page` would live forever! What is interesting, is simply removing the
   Grid's `Style` solved the problem?!?
   
   I narrowed this down to a unit test:
   
       [Fact]
       public async Task ColumnDefinitionDoesNotLeak()
       {
           // Long-lived column, like from a Style in App.Resources
           var column = new ColumnDefinition();
           WeakReference reference;
   
           {
               var grid = new Grid();
               grid.ColumnDefinitions.Add(column);
               reference = new(grid);
           }
   
           await Task.Yield();
           GC.Collect();
           GC.WaitForPendingFinalizers();
   
           Assert.False(reference.IsAlive, "Grid should not be alive!");
       }
   
   https://github.com/dotnet/maui/blob/cda3eb3381cfb686567ed05e3eb8e8f26c02d785/src/Controls/src/Core/Layout/Grid.cs#L20
   
   `Grid` subscribes to `DefinitionCollection<T>.ItemSizeChanged`, and in
   this case the `DefinitionCollection<T>` lived indefinitely in an
   application-wide `ResourceDictionary`.
   
   The simplest solution is to make the `ItemSizeChanged` event use
   `WeakEventManager` as was done for other events like
   `Application.RequestedThemeChanged`:
   
   https://github.com/dotnet/maui/blob/cda3eb3381cfb686567ed05e3eb8e8f26c02d785/src/Controls/src/Core/Application/Application.cs#L221-L225
   
   Since MAUI owns the property, we can use the simple solution here.
   
   This is one issue solved in the customer app, but I will need to retest
   the app in dotnet#15860 to see if there are further issues.

   

   jonathanpeppers committed Jul 13, 2023
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