求助：Xamarin.Forms启用ScrollView后SignaturePad无法使用

I totally get the frustration here—when you drop the SignaturePadView inside a ScrollView, the scroll container intercepts the touch events the signature pad needs to capture strokes properly. Let’s walk through two reliable fixes to get your signature functionality working again:

Approach 1: Custom ScrollView to Ignore SignaturePad Touches (Most Reliable) #

Create a custom ScrollView that detects when touches are targeting the SignaturePadView and lets the pad handle those events instead of triggering a scroll.

Step 1: Shared Project Custom ScrollView #

using Xamarin.Forms;

namespace App4
{
    public class SignatureFriendlyScrollView : ScrollView
    {
        public static readonly BindableProperty IgnoreViewProperty = BindableProperty.Create(
            nameof(IgnoreView), typeof(View), typeof(SignatureFriendlyScrollView), null);

        public View IgnoreView
        {
            get => (View)GetValue(IgnoreViewProperty);
            set => SetValue(IgnoreViewProperty, value);
        }
    }
}

Step 2: Platform-Specific Renderers #

Android Renderer (Add to your Android project)

using Android.Content;
using App4;
using App4.Droid;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;

[assembly: ExportRenderer(typeof(SignatureFriendlyScrollView), typeof(SignatureFriendlyScrollViewRenderer))]
namespace App4.Droid
{
    public class SignatureFriendlyScrollViewRenderer : ScrollViewRenderer
    {
        public SignatureFriendlyScrollViewRenderer(Context context) : base(context) { }

        public override bool OnInterceptTouchEvent(Android.Views.MotionEvent ev)
        {
            var scrollView = (SignatureFriendlyScrollView)Element;
            if (scrollView.IgnoreView != null)
            {
                var ignoreViewRenderer = Platform.GetRenderer(scrollView.IgnoreView);
                var ignoreViewNative = ignoreViewRenderer.View;

                var touchX = ev.GetX();
                var touchY = ev.GetY();

                var viewLocation = new int[2];
                ignoreViewNative.GetLocationOnScreen(viewLocation);
                var viewRect = new Android.Graphics.Rect(
                    viewLocation[0], viewLocation[1],
                    viewLocation[0] + ignoreViewNative.Width,
                    viewLocation[1] + ignoreViewNative.Height);

                if (viewRect.Contains((int)touchX, (int)touchY))
                {
                    // Let the signature pad handle the touch event instead of scrolling
                    return false;
                }
            }
            return base.OnInterceptTouchEvent(ev);
        }
    }
}

iOS Renderer (Add to your iOS project)

using App4;
using App4.iOS;
using CoreGraphics;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;

[assembly: ExportRenderer(typeof(SignatureFriendlyScrollView), typeof(SignatureFriendlyScrollViewRenderer))]
namespace App4.iOS
{
    public class SignatureFriendlyScrollViewRenderer : ScrollViewRenderer
    {
        public override bool ShouldBeginPanGesture(UIGestureRecognizer gestureRecognizer)
        {
            var scrollView = (SignatureFriendlyScrollView)Element;
            if (scrollView.IgnoreView != null)
            {
                var ignoreViewRenderer = Platform.GetRenderer(scrollView.IgnoreView);
                var ignoreViewNative = ignoreViewRenderer.NativeView;

                var touchLocation = gestureRecognizer.LocationInView(ignoreViewNative.Superview);
                var viewFrame = ignoreViewNative.Frame;

                if (viewFrame.Contains(touchLocation))
                {
                    // Skip scrolling if touch is on the signature pad
                    return false;
                }
            }
            return base.ShouldBeginPanGesture(gestureRecognizer);
        }
    }
}

Step 3: Update Your XAML #

Swap the default ScrollView with your custom one, and link it to your SignaturePadView:

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:acr="clr-namespace:Acr.XamForms.SignaturePad;assembly=Acr.XamForms.SignaturePad"
             xmlns:local="clr-namespace:App4"
             x:Class="App4.newpage">
    <ContentPage.Content>
        <local:SignatureFriendlyScrollView Orientation="Vertical" IgnoreView="{x:Reference padView}">
            <StackLayout>
                <Button Text="button1"/>
                <Button Text="button2"/>
                <Button Text="button3"/>
                <Button Text="button4"/>
                <Button Text="button5"/>
                <Button Text="button6"/>
                <Button Text="button7"/>
                <Button Text="button8"/>
                <acr:SignaturePadView x:Name="padView" 
                                      HeightRequest="320" 
                                      WidthRequest="240" 
                                      BackgroundColor="White" 
                                      CaptionText="Caption This" 
                                      CaptionTextColor="Black" 
                                      ClearText="Clear Me!" 
                                      ClearTextColor="Red" 
                                      PromptText="Prompt Here" 
                                      PromptTextColor="Red" 
                                      SignatureLineColor="Aqua" 
                                      StrokeColor="Black" 
                                      StrokeWidth="2" />
            </StackLayout>
        </local:SignatureFriendlyScrollView>
    </ContentPage.Content>
</ContentPage>

Approach 2: Quick Fix (Simple, Edge Cases Exist) #

If you want to avoid custom renderers, temporarily disable scroll when the user interacts with the signature pad:

Add This to Your Code-Behind #

using Xamarin.Forms;

namespace App4
{
    public partial class newpage : ContentPage
    {
        public newpage()
        {
            InitializeComponent();

            // Disable scroll when pad is tapped
            var padTap = new TapGestureRecognizer();
            padTap.Tapped += (s, e) =>
            {
                if (padView.Parent is ScrollView scrollView)
                {
                    scrollView.IsEnabled = false;
                }
            };
            padView.GestureRecognizers.Add(padTap);

            // Re-enable scroll when tapping outside the pad
            var pageTap = new TapGestureRecognizer();
            pageTap.Tapped += (s, e) =>
            {
                if (padView.Parent is ScrollView scrollView)
                {
                    scrollView.IsEnabled = true;
                }
            };
            Content.GestureRecognizers.Add(pageTap);
        }
    }
}

Note: This works for basic use but has edge cases (e.g., scrolling immediately after signing), so the custom renderer approach is better for production apps.

内容的提问来源于stack exchange，提问作者Manthiram