Ytukyg

On Xamarin Forms 3.3, I can't scroll ListView to top on iOS.

I try: Scrolling to start of Xamarin Forms ListView with header
But Can't set scroll ListView to top.
This is my code:

At control iOS:

public class ExtListViewRenderer : ListViewRenderer

{

    protected override void OnElementChanged(ElementChangedEventArgs<ListView> e) => iOS.Control.Logger.InvokeAction(() =>

    {

        base.OnElementChanged(e);



        if (!(e.NewElement is ExtListView extListView) || Control == null)

            return;



        extListView.EventScrollToTop += OnScrollToTop;

    });



    public void OnScrollToTop(object sender, EventArgs eventArgs)

    {

        Control.ScrollRectToVisible(new CoreGraphics.CGRect(0, 0, 1, 1), true);

    }



}

At class control:

public class ExtListView : ListView

{

    public event EventHandler EventScrollToTop;



    /// <summary>

    /// Scroll LisView To Top

    /// </summary>

    /// <param name="animate"></param>

    public void ScrollToTop(bool animate = true)

    {

        //bool animate is not used at this stage, it's always animated.

        EventScrollToTop?.Invoke(this, EventArgs.Empty);

    }

}

At view .xaml:

    <control:ExtListView.Behaviors>

        <common:MethodToDelegateBehavior Delegate="{Binding ScrollToTop}"

                                         DelegateType="{x:Type propertyViewModels:PropertyPageViewModel+ScrollToTopDelegate}"

                                         MethodName="ScrollToTop" />

    </control:ExtListView.Behaviors>

At page:

    public delegate void ScrollToTopDelegate(bool animate);

    private ScrollToTopDelegate _scrollToTop;

    public ScrollToTopDelegate ScrollToTop

    {

        get => _scrollToTop;

        set => this.RaiseAndSetIfChanged(ref _scrollToTop, value);

    }

At method use:

ScrollToTop?.Invoke(true);

• I use it on Android is work, but iOS is not work.

This is my idea:

• Use method ScrollTo of Class ListView (ScrollTo).


• Set item focus on ListView is first item and ScrollToPosition is ScrollToPosition.Start
  

(use animated = true if you want to see the scroll happen)

Create a flag: ScrollToTop = true use at layout .xaml that handler change Scroll of ListView.

You try it:

 var firstItem = ((IEnumerable<object>)extListView.ItemsSource)?.FirstOrDefault();

 if (firstItem != null)

     extListView.ScrollTo(firstItem, ScrollToPosition.Start, false);

Hope it can help you!

I use the following code to scroll my ListView classes to a specific position.

Control.SetContentOffset(new CGPoint(Control.ContentOffset.X, y), animated);

When scrolling, X normally will not change, but Y is the value you would like changed. Using that code scrolling to the top would be like this:

// You can send true for the animate property whether or not you want to see the scroll happen

Control.SetContentOffset(new CGPoint(Control.ContentOffset.X, 0), true);