Troubleshooting Memory Issues

Uno Platform provides a set of classes aimed at diagnosing memory issues related to leaking controls, whether it be from an Uno.UI issue or from an invalid pattern in user code.

WebAssembly memory profiling

Starting from Uno.Wasm.Bootstrap 3.2, the Xamarin Profiler can be used to profile memory usage. See this documentation for additional details.

Enable Memory instances counter

1. Install the Uno.Core NuGet package;

2. In your application, as early as possible in the initialization (generally in the App.cs or App.xaml.cs constructor), add and call the following method:

   using Uno.UI.DataBinding;
   using Uno.UI.DataBinding;
   using System.Threading.Tasks;
   using Uno.Extensions;
   using Uno.Logging;
   
   // ....
   private void EnableViewsMemoryStatistics()
   {
   //
   // Call this method to enable Views memory tracking.
   // Make sure that you've added the following :
   //
           //  builder.AddFilter("Uno.UI.DataBinding", LogLevel.Information );
   //
   // in the logger settings, so that the statistics are showing up.
   //
   
   var unused = Windows.UI.Xaml.Window.Current.Dispatcher.RunAsync(
     CoreDispatcherPriority.Normal,
     async () =>
     {
     BinderReferenceHolder.IsEnabled = true;
   
     while (true)
     {
       await Task.Delay(1500);
   
       try
       {
       BinderReferenceHolder.LogReport();
   
       var inactiveInstances = BinderReferenceHolder.GetInactiveViewBinders();
   
       // Force the variable to be kept by the linker so we can see it with the debugger.
       // Put a breakpoint on this line to dig into the inactive views.
       inactiveInstances.ToString();
       }
       catch (Exception ex)
       {
       this.Log().Error("Report generation failed", ex);
       }
     }
     }
   );
   }
   

   You'll also need to add the following logger filter:

   builder.AddFilter("Uno.UI.DataBinding.BinderReferenceHolder", LogLevel.Information );
   

   As well as this package NuGet (you will need to update to the latest Uno.UI nuget version):

   <PackageReference Include="Uno.UI.Adapter.Microsoft.Extensions.Logging" Version="4.0.13" />
   

It is also possible to create diffs between memory snapshots by using the BinderReferenceHolder.LogInactiveViewReferencesStatsDiff method.

Interpreting the statistics output

The output provides two sets of DependencyObject in memory:

• Active, for which the instances have a parent dependency object (e.g. an item in a Grid)
• Inactive, for which the instances do not have a parent dependency object

When doing back and forth navigation between pages, instances of the controls in the dismissed pages should generally be collected after a few seconds, once those have been cleared from the Frame control's forward stack (done after every new page navigation).

Searching for inactive objects first is generally best, as those instances are most likely kept alive by cross references.

This can happen when a Grid item has a strong field reference to its parent:

var myItem = new Grid(){ Tag = grid };
grid.Children.Add(myItem);

For Xamarin.iOS specifically, see this article about performance tuning.