Xamarin Forms - detect when user starts to scroll down in a scrollview

Question

I have a scrollview which, as soon as the user starts to scroll up, I run some code (OnSwipeUp()). I detect this using

textScroll.Scrolled += (sender, e) => { onScrolled(); };

private void onScrolled()
{
      if(textScroll.ScrollY > 0)
      {
          OnSwipeUp(null, null);
      }
}

I also need to detect when the user start scrolling down, so I was thinking of getting the max Y position of the scrollview then say something like

if(textScroll.ScrollY < maxY)

Am I able to do this?

Answer 1

Try this:

private double previousScrollPosition = 0;
void Handle_Scrolled(object sender, Xamarin.Forms.ScrolledEventArgs e) 
{

  if (previousScrollPosition < e.ScrollY) 
  {
    //scrolled down
    previousScrollPosition = e.ScrollY;
  } 
  else 
  {
      //scrolled up

    if (Convert.ToInt16(e.ScrollY) == 0)
    previousScrollPosition = 0;

  }
}

Answer 2

You do not need to get the max Y position because before scrolling down, the Y position is always 0. So you just have to get the direction of scrolling. I wrote a demo to prove this:

MainPage.xaml.cs

private double previousScrollPosition = 0;

        public MainPage()
        {
            InitializeComponent();
        }

        void Handle_Scrolled(object sender, Xamarin.Forms.ScrolledEventArgs e)
        {
            if (previousScrollPosition < e.ScrollY)
            {
                //scrolled down
                Console.WriteLine("!!!!!!!!!scrolled down   ScrollY=>" + textScroll.ScrollY);
            }
            else
            {
                //scrolled up
                Console.WriteLine("!!!!!!!!!scrolled up   ScrollY=>" + textScroll.ScrollY);
            }
            previousScrollPosition = e.ScrollY;
        }

MainPage.xaml

<ContentPage.Content>
        <StackLayout>
            <BoxView BackgroundColor="Red" HeightRequest="200" WidthRequest="150" />
            <ScrollView x:Name="textScroll" Scrolled="Handle_Scrolled">
                <StackLayout>
                    <Entry Text="aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"/>
                    <Entry Text="bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"/>
                    <Entry Text="ccccccccccccccccccccccccccccccccccccccccccccccccccc"/>
                    <Entry Text="ddddddddddddddddddddddddddddddddddddddddddddddddddddddddd"/>
                    <Entry Text="eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee"/>
                    <Entry Text="fffffffffffffffffffffffffffffffffffffffffff"/>
                    <Entry Text="ggggggggggggggggggggggggggggggggggggggggggggg"/>
                    <Entry Text="aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"/>
                    <Entry Text="bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"/>
                    <Entry Text="ccccccccccccccccccccccccccccccccccccccccccccc"/>
                    <Entry Text="dddddddddddddddddddddddd"/>
                    <Entry Text="eeeeeeeeeeeeeeeeeeeeeeeeee"/>
                    <Entry Text="fffffffffffffffffffffffffffffffffffffffffff"/>
                    <Entry Text="ggggggggggggggggggggggggggggggggggggggggggggg"/>
                    <Entry Text="aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"/>
                    <Entry Text="bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"/>
                    <Entry Text="ccccccccccccccccccccccccccccccccccccccccccccccccccc"/>
                    <Entry Text="ddddddddddddddddddddddddddddddddddddddddddddddddddddddddd"/>
                    <Entry Text="eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee"/>
                    <Entry Text="fffffffffffffffffffffffffffffffffffffffffff"/>
                    <Entry Text="ggggggggggggggggggggggggggggggggggggggggggggg"/>
                    <Entry Text="aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"/>
                    <Entry Text="bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"/>
                    <Entry Text="ccccccccccccccccccccccccccccccccccccccccccccc"/>
                    <Entry Text="dddddddddddddddddddddddd"/>
                    <Entry Text="eeeeeeeeeeeeeeeeeeeeeeeeee"/>
                    <Entry Text="fffffffffffffffffffffffffffffffffffffffffff"/>
                    <Entry Text="ggggggggggggggggggggggggggggggggggggggggggggg"/>
                </StackLayout>
            </ScrollView>

        </StackLayout>

    </ContentPage.Content>