Uno.UI - Performance

This article lists a number of performance tips to optimize your Uno Platform application.

Here's what to look for:

  • Make sure to always have the simplest visual tree. There's nothing faster than something you don't draw.

  • Reduce panels in panels depth. Use Grids and relative panels where possible.

  • Force the size of images anywhere possible

  • When binding the Visibility property, make sure to always set TargetNullValue and FallbackValue to collapsed : Visibility="{Binding [IsAvailable], Converter={StaticResource boolToVisibility}, FallbackValue=Collapsed, TargetNullValue=Collapsed}"

  • Collapsed elements are not considered when measuring and arranging the visual tree, which makes them almost costless.

  • When binding or animating (via visual state setters) the visibility property, make sure to enable lazy loading: x:Load="False".

  • Use x:Load={x:Bind MyVisibility} where appropriate as toggling to from true false effectively removes a part of the visual tree from memory. Note that setting back to true re-creates the visual tree.

  • ListView and GridView

    • Don't use template selectors inside the ItemTemplate, prefer using the ItemTemplateSelector on ListView/GridView.

    • The default ListViewItem and GridViewItem styles are very feature rich, yet that makes them quite slow. For instance, if you know that you're not likely to use selection features for a specific ListView, create a simpler ListViewItem style that some visual states, or the elements that are only used for selection.

    • If items content frequently change (e.g. live data in TextBlock) on iOS and Android, ListView items rendering can require the use of the xamarin:AreDimensionsConstrained="True" uno-specific property. This attribute prevents items in a list from requesting their parent to be re-measured when their properties change. It's safe to use the AreDimensionsConstrained property when items always have the same size regardless of bound data, and the items and list are stretched in the non-scrolling direction. If item sizes can change when the bound data changes (eg, if they contain bound text that can wrap over multiple lines, images of undetermined size, etc), or if the list is wrapped to the items, then you shouldn't set AreDimensionsConstrained because the list does need to remeasure itself when item data changes in that case.

      You'll need to set the property on the top-level element of your item templates, as follows:

        <ResourceDictionary xmlns:xamarin="http://uno.ui/xamarin" mc:Ignorable="d xamarin" ...>
        	<DataTemplate x:Key="MyTemplate">
        		<Grid Height="44" xamarin:AreDimensionsConstrained="True">

      Note that WinUI does not need this, and the issue is tracked in Uno here.

  • Updating items in ItemsControl can be quite expensive, using ItemsRepeater is generally faster at rendering similar content.

  • Animations

    • Prefer Opacity animations to Visibility animations (this avoids some measuring performance issues).
      • Unless the visual tree of the element is very big, where in this case Visibility is better suited.
    • Prefer Storyboard setters to ObjectAnimationUsingKeyFrames if there is only one key frame.
    • Prefer changing the properties of a visual element instead of switching opacity or visibility of an element.
      • Manually created Storyboard instances do not stop automatically. Make sure that if you invoke Storyboard.Begin(), invoke Storyboard.Stop() when the animated content is unloaded, otherwise resources may be spent animating invisible content.
      • ProgressRing and ProgressBar controls indeterminate mode generally consume rendering time. Make sure to set those to determinate modes when not visible.
      • Troubleshooting of animations can be done by enabling the following logger:
          builder.AddFilter("Windows.UI.Xaml.Media.Animation", LogLevel.Debug);
        The logger will provide all the changes done to animated properties, with element names.
  • Image Assets

    • Try using an image that is appropriate for the DPI and screen size.
    • Whenever possible, specify and explicit Width and Height on Image.
    • The pixel size of an image will impact the loading time of the image. If the image is intentionally blurry, prefer reducing the physical size of the image over the compressed disk size of the image.
  • Paths

    • Prefer reusing paths, duplication costs Main and GPU memory.
    • Prefer using custom fonts over paths where possible. Fonts are rendered extremely fast and have a very low initialization time.
  • Bindings

    • Prefer bindings with short paths.
    • To shorten paths, use the DataContext property on containers, such as StackPanel or Grid.
    • As of Uno 3.9, adding a control to loaded Panel or ContentControl does propagate the parent's DataContext immediately. If the new control has its DataContext immediately overridden to something else, ensure to set the DataContext before adding the control to its parent.T his will avoid having bindings be refreshed twice needlessly.
    • Add the Windows.UI.Xaml.BindableAttribute or System.ComponentModel.BindableAttribute on non-DependencyObject classes.
      • When data binding to classes not inheriting from DependencyObject, in Debug configuration only, the following message may appear:
          The Bindable attribute is missing and the type [XXXX] is not known by the MetadataProvider.
          Reflection was used instead of the binding engine and generated static metadata. Add the Bindable 	attribute to prevent this message and performance issues.
        This message indicates that the binding engine will fall back on reflection based code, which is generally slow. To compensate for this, Uno use the BindableTypeProvidersSourceGenerator, which generates static non-generic code to avoid reflection operations during binding operations. This attribute is inherited and is generally used on ViewModel based classes.
  • x:Phase

    • For ListView instances with large templates, consider the use of x:Phase to reduce the number of bindings processed during item materialization.
    • It is only supported for items inside ListViewItem templates, it will be ignored for others.
    • It is also supported as xamarin:Phase on controls that do not have bindings. This feature is not supported by UWP.
    • It is only supported for elements under the DataTemplate of a ListViewItem. The attribute is ignored for templates of ContentControl instances, or any other control.
    • When binding to Brushes with a solid color, prefer binding to the Color property like this if the brush type does not change:
      <TextBlock Text="My Text">
              <SolidColorBrush Color="{x:Bind Color, Mode=OneWay, FallbackValue=Red}" />
  • Resources

    • Avoid using x:Name in ResourceDictionary as those force early instantiation of the resource
    • Use Uno.XamlMerge.Task to merge all top-level AppResources.xaml or App.xaml resource dictionaries

WebAssembly specifics

  • Building your application in Release configuration is critical to get the best performance.
  • Make sure to use the latest stable release of Uno.Wasm.Bootstrap packages
  • Enable AOT or PG-AOT to get the best performance.
  • When recording a PG-AOT profile, make sure to run through most of your application because saving the profile.
  • Adjusting the GC configuration may be useful to limit the collection runs on large allocations. Add the following to your csproj file:
      	<WasmShellMonoEnvironment Include="MONO_GC_PARAMS" Value="soft-heap-limit=512m,nursery-size=64m,evacuation-threshold=66,major=marksweep" />
    You can adjust the nursery-size and soft-heap-limit based on your application's memory consumption characteristics.
  • The size of the application can be reduced by:

Advanced performance Tracing

Profiling applications

A profiling guide for Uno Platform apps is available here.


The framework template pool manages the pooling of ControlTemplates and DataTemplates, and in most cases, the recycling of controls should be high.

  • CreateTemplate is raised when a new instance of a template is created. This is an expensive operation that should be performed as rarely as possible.
  • RecycleTemplate is raised when an active instance of a template is placed into the pool. This should happen often.
  • ReuseTemplate is raised when a pooled template is provided to a control asking for a specific data template.
  • ReleaseTemplate is raised when a pooled template instance has not been used for a while.

If the ReuseTemplate occurrences is low, this usually means that there is a memory leak to investigate.