LazyView

[kphillpotts]

LazyView

• Proposed
• Prototype: Not Started
• Implementation: Not Started
  • iOS Support
  • Android Support
  • macOS Support
  • Windows Support
• Unit Tests: Not Started
• Sample: Not Started
• Documentation: Not Started

Summary

The LazyView control allows you to delay the initialization of a View. You need to provide the type of the View that you want to be rendered, using the x:TypeArguments XAML namespace attribute, and handle its initialization using the LoadViewAsync method. The IsLoaded property can be examined to determine when the LazyView is loaded.

Note: This proposal is a to port the existing LazyView functionality from the Xamarin Community Toolkit

• Existing Docs
• Xamarin Community Toolkit Implementation

Motivation

LazyView is one of the views that exist in the Xamarin Community Toolkit that has been requested as a missing piece in the migration of some big apps from Xamarin to MAUI.

Detailed Design

To provide a migration path forward from Xamarin Community Tookit, I see no reason to update the API surface area, as such it would be:

Properties:

Property	Type	Description
IsLoaded	bool	Gets the loaded status of the LazyView.

Methods:

Method	Return Type	Description
LoadViewAsync	ValueTask	Initialize the View.
Dispose	void	Cleans up the View, if required.

XAML Usage

     <StackLayout>
        <toolkit:LazyView x:TypeArguments="local:LazyTestView" IsLoaded = "{Binding IsLoaded}" />
    </StackLayout>

C# Implementation of a LazyView derived

/// <summary>
/// This a basic implementation of the LazyView based on <see cref="BaseLazyView"/> use this an exemple to create yours
/// </summary>
/// <typeparam name="TView">Any <see cref="View"/></typeparam>
public class LazyView<TView> : BaseLazyView where TView : View, new()
{
  /// <summary>
  /// This method initializes your <see cref="LazyView{TView}"/>.
  /// </summary>
  /// <returns><see cref="ValueTask"/></returns>
  public override ValueTask LoadViewAsync()
  {
    View view = new TView { BindingContext = BindingContext };
    
    Content = view;
    
    SetIsLoaded(true);
    return new ValueTask(Task.FromResult(true));
  }
}

Drawbacks

No drawbacks I'm aware of, other than potentially competing priorities

Unresolved Questions

• Are there any complications with a straight port across due to MAUI changes?
• Are there any feature requests, bugs that should be resolved at the time of porting

[bijington]

The usage of new TView requires a parameterless constructor which matches what we had in Xamarin however could/should we allow for more power through the magic of DI?

[bijington]

Is this a duplicate of #112? Or vice-versa?

[bijington]

@kphillpotts is this something you are looking at implementing or would you be willing for some help? I need to find something to get involved with now.

[VladislavAntonyuk]

Closing as duplicate of #112