readme.md

MPowerKit.VirtualizeListView

MAUI Virtualize ListView with smooth scrolling and without platform-specific code

It's not a secret to anybody, that ListView and CollectionView in MAUI have bad scrolling performance. This project started as an experimantal project POC to find a way to make a virtualize listview using ScrollView and AbsoluteLayout only. Suprisingly, the scrolling performance is way better, than was expected. So you can check it right now.

It works on all platforms MAUI supports and it has the same behavior on all platforms, because it does not have platform-specific code.

So, under the hood it is a ScrollView with custom typeof(Layout) as items layout. The main idea of virtualization for this listview is to change Translation (virtual position, but on Android it is still physical chage because of #5) of items while keeping them attached to the layout. VirtualizeItemsLayoutManger is responsible for virtualization process and for creating / removing views and it will not create more views as necessary.

Your PRs are welcome!

Android	Windows
android.mp4	windows.mp4

Implemented features:

• Linear items layout
• Grid items layout
• Items spacing
• Virtualization
• Grouping
• Collection padding
• Scroll orientation (collection orientation)
• Disable scrolling
• Header / Footer
• Load more
• Scroll speed
• Cache pool
• Item tap handling
• Item resize handling
• Add, Remove, Replace, Move, Reset operations on collection
• Drag and drop (reordering)
• Sticky headers
• Animated add/remove/move operations

Tips for better scrolling user experience

• Bindings - your enemy. Try to avoid bindings in your item templates or do OneTime where you can. But if you need them, use only compiled bindings or better levitali/CompiledBindings library.
• Try to avoid using triggers, they are slow.
• Use as less templates as possible. The more templates you have, the more time it takes to create a view.
• Use InitialCachePoolSize to set up the number of initial views to keep in cache. Default size is 4. The bigger value - the more cached views it creates during initialization. And if you have a lot of templates it can take some time to initialize pool for each template. So in this case just manipulate with the InitialCachePoolSize. If you have only 1 template, you can set it to 2, it will be enough.
• Create separate view for DataTemplate and replace bindings where you can by manual setting the values from the code behind of that view.
• Use as less layouts as possible. Use only ContentView, Grid, VerticalStackLayout or HorizontalStackLayout. Try to avoid using Border or Frame, better create RoundBorderEffect.
• Try to avoid using Shadow property in your templates. It can slow down the rendering process.
• Set the direct dimensions for your controls where you can in the template, especially for Image.
• If you have very complex layout and the VirtualizeListView still not smooth and laggy, you can try to decrease ScrollSpeed, it may help in some cases. (MAUI does a lot of redundant work remeasuring and relayouting views few times).

Usage

Add UseMPowerKitListView() to your MauiProgram.cs file as next

builder
    .UseMauiApp<App>()
    .UseMPowerKitListView();

and in your xaml just use as a regular CollectionView.

Note: The root of the ItemTemplate has to be typeof(VirtualizeListViewCell), but group/header/footer templates are not allowed to have root of this type.

ItemsLayout

By default VirtualizeListView using LinearLayout as items layout and it has zero items spacing.

To change items spacing you need to reset the ItemsLayout property. If you want to use LinearLayout:

<mpowerkit:VirtualizeListView>
	<mpowerkit:VirtualizeListView.ItemsLayout>
		<mpowerkit:LinearLayout ItemSpacing="15" 
		                        InitialCachePoolSize="4" /> <!-- InitialCachePoolSize is optional, default value is 4 -->
	</mpowerkit:VirtualizeListView.ItemsLayout>
</mpowerkit:VirtualizeListView>

or if you want to use GridLayout:

<mpowerkit:VirtualizeListView>
	<mpowerkit:VirtualizeListView.ItemsLayout>
		<mpowerkit:GridLayout HorizontalItemSpacing="15"
                              Span="3"
                              VerticalItemSpacing="15" />
	</mpowerkit:VirtualizeListView.ItemsLayout>
</mpowerkit:VirtualizeListView>

Grouping / Header / Footer

if you need to add groups, your ItemsSource has to be typeof(IEnumerable<IEnumerable<>>), then you need to set IsGrouped="True" on VirtualizeListView and you need to add Group Header/Footer templates as next:

<mpowerkit:VirtualizeListView.GroupHeaderTemplate>
    <DataTemplate x:DataType="YourGroupType">
        <Grid Padding="15" >
            <Label Text="{Binding SomeProperty}" />
        </Grid>
    </DataTemplate>
</mpowerkit:VirtualizeListView.GroupHeaderTemplate>

If you need Header / Footer you need to set data to Header or Footer properties of the VirtualizeListView, usually this is just your page's viewmodel, but it can be any data as you want, then you need to declare header/footer template as next:

<mpowerkit:VirtualizeListView.HeaderTemplate>
    <DataTemplate x:DataType="YourHeaderType">
        <Grid Padding="15">
            <Label Text="{Binding SomeProperty}" />
        </Grid>
    </DataTemplate>
</mpowerkit:VirtualizeListView.HeaderTemplate>

Load more

To enable load more feature you need to set ThresholdCommand="{Binding LoadMoreCommand}". Also you may set RemainingItemsThreshold (how many items before the end trigger the ThresholdCommand), by default it is 5.

Other properties

You may want to know when user taps on cell, for this you have ItemTapCommand, the command parameter is the BindingContext of the cell.

To change collection orientation just change the Orientation property of the VirtualizeListView as you would do this in ScrollView.

To disable scroll set CanScroll property to false, and do not change Orientation property to Neither.

Other useful features of this package

FixedRefreshView

This package brings to you fixed MAUI's RefreshView as FixedRefreshView. Here, you can disable refreshing without disabling entire collection. For this you may use IsPullToRefreshEnabled.

ObservableRangeCollection

Also, this package contains ObservableRangeCollection which is an ObservableCollection, but it has a bunch of useful methods to manipulate the collection with batch updates. Recommended to use with VirtualizeListView. It provides few methods: AddRange, InsertRange, RemoveRange, ReplaceRange.

Known issues

• In debug mode it can have bad scrolling performance, especially on Windows, but in release mode it works surprisingly very well.