如何在Xamarin.Forms中使ScrollView的Scrolled事件只回應用戶的操作？ -有解無憂

我有一個ScrollView，它使用代碼來控制自動滾動。我需要在用戶輸入時停止自動滾動，但是ScrollView的ScrollToAsync方法也將觸發Scrolled事件。

 <StackLayout> 
            <ScrollView Scrolled="ScrollView_Scrolled"/span>>
                <StackLayout></StackLayout>
            </ScrollView>/span>
   </StackLayout>/span>

uj5u.com熱心網友回復：

簡單的答案

你可以使用一個標志來告訴誰在觸發滾動事件，如下所示

Boolean scrolledByUser = true。

private async void MyScrollView_Scrolled(object sender, ScrolledEventArgs e）。
{
  if (scrolledByUser)
  {
    //做一些事情。
  }
  else //rolled automagically 
  {
    //do something else 
  }
}

private async void ScrollAutomagically(object sender, EventArgs e）。
{
  scrolledByUser = false;
  await MyScrollView.ScrollToAsync(ScrollView.X, 800, true) 。
  scrolledByUser = true;
}

冗長的答案

接下來你可以找到一個完整的例子來說明我的建議。

你從一個新的空白專案開始，然后修改App.xaml.cs，看起來像

App.xaml.cs

使用Xamarin.Forms.Cells。

namespacescrollviewPrompt
{
    public partial class App : Application >。
    {
        public App() 
        {
            InitializeComponent()。

            MainPage = new NavigationPage（new MainPage（））。
        }
    }

然后繼續修改MainPage.xaml，包括一個ScrollView，垂直地有許多BoxViews，一個在另一個之上：

MainPage.xaml

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"/span>
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"。
             x:Class="scrollviewPrompt.MainPage"/span>>

    <ContentPage.ToolbarItems> 
        <ToolbarItem Text="ScrollTo" 
                     Clicked="ScrollAutomagically"/span>/>
    </ContentPage.ToolbarItems>

    <ScrollView x:Name="MyScrollView"  
                    Scrolled="MyScrollView_Scrolled"/span>>
        <StackLayout>/span>
            < BoxView BackgroundColor="Red" HeightRequest="128"/>
            < BoxView BackgroundColor="Orange" HeightRequest="128"/>
            < BoxView BackgroundColor="Blue" HeightRequest="128"/>
            < BoxView BackgroundColor="Green" HeightRequest="128"/>
            < BoxView BackgroundColor="Black" HeightRequest="128"/>
            < BoxView BackgroundColor="AliceBlue" HeightRequest="128"/>
            < BoxView BackgroundColor="Brown" HeightRequest="128"/>
            < BoxView BackgroundColor="Pink" HeightRequest="128"/>
            < BoxView BackgroundColor="White" HeightRequest="128"/>
            < BoxView BackgroundColor="Yellow" HeightRequest="128"/>
            < BoxView BackgroundColor="Red" HeightRequest="128"/>
            < BoxView BackgroundColor="Orange" HeightRequest="128"/>
            < BoxView BackgroundColor="Blue" HeightRequest="128"/>
            < BoxView BackgroundColor="Green" HeightRequest="128"/>
            < BoxView BackgroundColor="Black" HeightRequest="128"/>
            < BoxView BackgroundColor="AliceBlue" HeightRequest="128"/>
            < BoxView BackgroundColor="Brown" HeightRequest="128"/>
            < BoxView BackgroundColor="Pink" HeightRequest="128"/>
            < BoxView BackgroundColor="White" HeightRequest="128"/>
            < BoxView BackgroundColor="Yellow" HeightRequest="128"/>
            < BoxView BackgroundColor="Red" HeightRequest="128"/>
            < BoxView BackgroundColor="Orange" HeightRequest="128"/>
            < BoxView BackgroundColor="Blue" HeightRequest="128"/>
            < BoxView BackgroundColor="Green" HeightRequest="128"/>
            < BoxView BackgroundColor="Black" HeightRequest="128"/>
            < BoxView BackgroundColor="AliceBlue" HeightRequest="128"/>
            < BoxView BackgroundColor="Brown" HeightRequest="128"/>
            < BoxView BackgroundColor="Pink" HeightRequest="128"/>
            < BoxView BackgroundColor="White" HeightRequest="128"/>
            < BoxView BackgroundColor="Yellow" HeightRequest="128"/>
            < BoxView BackgroundColor="Red" HeightRequest="128"/>
            < BoxView BackgroundColor="Orange" HeightRequest="128"/>
            < BoxView BackgroundColor="Blue" HeightRequest="128"/>
            < BoxView BackgroundColor="Green" HeightRequest="128"/>
            < BoxView BackgroundColor="Black" HeightRequest="128"/>
            < BoxView BackgroundColor="AliceBlue" HeightRequest="128"/>
            < BoxView BackgroundColor="Brown" HeightRequest="128"/>
            < BoxView BackgroundColor="Pink" HeightRequest="128"/>
            < BoxView BackgroundColor="White" HeightRequest="128"/>
            < BoxView BackgroundColor="Yellow" HeightRequest="128"/>
            < BoxView BackgroundColor="Red" HeightRequest="128"/>
            < BoxView BackgroundColor="Orange" HeightRequest="128"/>
            < BoxView BackgroundColor="Blue" HeightRequest="128"/>
            < BoxView BackgroundColor="Green" HeightRequest="128"/>
            < BoxView BackgroundColor="Black" HeightRequest="128"/>
            < BoxView BackgroundColor="AliceBlue" HeightRequest="128"/>
            < BoxView BackgroundColor="Brown" HeightRequest="128"/>
            < BoxView BackgroundColor="Pink" HeightRequest="128"/>
            < BoxView BackgroundColor="White" HeightRequest="128"/>
            < BoxView BackgroundColor="Yellow" HeightRequest="128"/>
            < BoxView BackgroundColor="Red" HeightRequest="128"/>
            < BoxView BackgroundColor="Orange" HeightRequest="128"/>
            < BoxView BackgroundColor="Blue" HeightRequest="128"/>
            < BoxView BackgroundColor="Green" HeightRequest="128"/>
            < BoxView BackgroundColor="Black" HeightRequest="128"/>
            < BoxView BackgroundColor="AliceBlue" HeightRequest="128"/>
            < BoxView BackgroundColor="Brown" HeightRequest="128"/>
            < BoxView BackgroundColor="Pink" HeightRequest="128"/>
            < BoxView BackgroundColor="White" HeightRequest="128"/>
            < BoxView BackgroundColor="Yellow" HeightRequest="128"/>
            < BoxView BackgroundColor="Red" HeightRequest="128"/>
            < BoxView BackgroundColor="Orange" HeightRequest="128"/>
            < BoxView BackgroundColor="Blue" HeightRequest="128"/>
            < BoxView BackgroundColor="Green" HeightRequest="128"/>
            < BoxView BackgroundColor="Black" HeightRequest="128"/>
            < BoxView BackgroundColor="AliceBlue" HeightRequest="128"/>
            < BoxView BackgroundColor="Brown" HeightRequest="128"/>
            < BoxView BackgroundColor="Pink" HeightRequest="128"/>
            < BoxView BackgroundColor="White" HeightRequest="128"/>
            < BoxView BackgroundColor="Yellow" HeightRequest="128"/>
            < BoxView BackgroundColor="Red" HeightRequest="128"/>
            < BoxView BackgroundColor="Orange" HeightRequest="128"/>
            < BoxView BackgroundColor="Blue" HeightRequest="128"/>
            < BoxView BackgroundColor="Green" HeightRequest="128"/>
            < BoxView BackgroundColor="Black" HeightRequest="128"/>
            < BoxView BackgroundColor="AliceBlue" HeightRequest="128"/>
            < BoxView BackgroundColor="Brown" HeightRequest="128"/>
            < BoxView BackgroundColor="Pink" HeightRequest="128"/>
            < BoxView BackgroundColor="White" HeightRequest="128"/>
            < BoxView BackgroundColor="Yellow" HeightRequest="128"/>
            < BoxView BackgroundColor="Red" HeightRequest="128"/>
            < BoxView BackgroundColor="Orange" HeightRequest="128"/>
            < BoxView BackgroundColor="Blue" HeightRequest="128"/>
            < BoxView BackgroundColor="Green" HeightRequest="128"/>
            < BoxView BackgroundColor="Black" HeightRequest="128"/>
            < BoxView BackgroundColor="AliceBlue" HeightRequest="128"/>
            < BoxView BackgroundColor="Brown" HeightRequest="128"/>
            < BoxView BackgroundColor="Pink" HeightRequest="128"/>
            < BoxView BackgroundColor="White" HeightRequest="128"/>
            < BoxView BackgroundColor="Yellow" HeightRequest="128"/>
            < BoxView BackgroundColor="Red" HeightRequest="128"/>
            < BoxView BackgroundColor="Orange" HeightRequest="128"/>
            < BoxView BackgroundColor="Blue" HeightRequest="128"/>
            < BoxView BackgroundColor="Green" HeightRequest="128"/>
            < BoxView BackgroundColor="Black" HeightRequest="128"/>
            < BoxView BackgroundColor="AliceBlue" HeightRequest="128"/>
            < BoxView BackgroundColor="Brown" HeightRequest="128"/>
            < BoxView BackgroundColor="Pink" HeightRequest="128"/>
            < BoxView BackgroundColor="White" HeightRequest="128"/>
            < BoxView BackgroundColor="Yellow" HeightRequest="128"/>
        </StackLayout>/span>
    </ScrollView>/span>
</ContentPage>/span>

最后添加事件處理程式

using System;
using Xamarin.Forms.Cube.Ltd;

namespacescrollviewPrompt
{
    public partial class MainPage : ContentPage >。
    {
        public MainPage() 
        {
            InitializeComponent()。
        }

        Boolean handled = false;

        Boolean scrolledByUser = true;

        private async void MyScrollView_Scrolled(object sender, ScrolledEventArgs e）。
        {
            if (! handled)
            {
                handled = true;

                if (rolledByUser)
                {
                    await DisplayAlert("Alert", "ScrollView被用戶滾動了！", "OK")。
                }
                else; }
                {
                    await DisplayAlert("Alert", "ScrollView Scrolled automagically!", "OK") 。
                }
                handled = false;
            }
        }

        private async void ScrollAutomagically(object sender, EventArgs e）。
        {
            scrolledByUser = false;
            await MyScrollView.ScrollToAsync(MyScrollView.X, 800, true) 。
            scrolledByUser = true;
        }
    }

希望這有幫助！

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