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Xamarin表单-检测用户何时开始在滚动视图中向下滚动

scrollview xamarin.forms c#

0

DarkW1nter · 技术社区 · 7 年前

我有一个scrollview,当用户开始向上滚动时,我会运行一些代码(onswipup())。我使用

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

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

我还需要检测用户何时开始向下滚动,所以我想得到scrollview的最大Y位置,然后说

if(textScroll.ScrollY < maxY)

我能做到吗?

0 回复 | 直到 7 年前

1

4

Himanshu Dwivedi 7 年前

试试这个:

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;

  }
}

2

1

AbbyWang - MSFT 7 年前

您不需要获取最大Y位置,因为在向下滚动之前,Y位置始终为0。所以你只需要知道滚动的方向。我写了一个演示来证明这一点:

主页。xaml。反恐精英

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;
        }

主页。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>