xamarin.forms webview.focused 事件在 Android 上引发，但不在 iOS 上引发

Question

I'm using a Xamarin.Forms grid application to show a couple of html elements as WebViews in the cells of the grid CardGrid:

    private async void CreateCardView()
    {
        CardGrid.Children.Clear();

        // idx over all count elements of html snippets
        for (idx = 0; idx < count; idx++)
        {
            string html = AuthoringCard(idx);
            RenderingCard(html, idx);
        }
    }

AuthoringCard() creates the html code snippet.

RenderingCard() creates the WebView inside the grid cell.

    private void RenderingCard(string htmlCard, int index)
    {
        int CardWidth = 300;
        int CardHeight = 150;
        int CardNoHorizontally = 3;

        WebView uiCard = new WebView();
        uiCard.HeightRequest = CardHeight - 5;
        uiCard.WidthRequest= CardWidth - 5;
        uiCard.VerticalOptions = LayoutOptions.Start;
        uiCard.HorizontalOptions = LayoutOptions.Center;
        uiCard.Margin = new Thickness(0);
        uiCard.AutomationId = index.ToString();
        uiCard.Focused += Card_Tapped;
        uiCard.InputTransparent = false;

        var htmlSource1 = new HtmlWebViewSource
        {
            Html = htmlCard,
        };
        uiCard.Source = htmlSource1;

        CardGrid.Children.Add(uiCard);

        int row = (int)Math.Floor((double)(index / CardNoHorizontally));
        int column = index - (row * CardNoHorizontally);

        Grid.SetRow(uiCard, row);
        Grid.SetColumn(uiCard, column);
    }

I want to catch the Focused event, when the user it tapping on the card (WebView) and using the AutomationId to get the index of the card (html code snippet):

    private void Card_Tapped(object sender, EventArgs e)
    {
        WebView card = (WebView)sender;

        int index = Convert.ToInt16(card.AutomationId));
    }

This works fine with Android. Under iOS the event is never raised. Any idea for a solution?

Answer 1

Cause:

the property Focus in Forms correspond method that we called becomeFirstResponder in native iOS platform.Unfortunately,UIWebView and WKwebview do not support the method becomeFirstResponder .This method is only available in some 'input-controls' Such as UITextField and UITextView(Entry in Forms).So even if you set the event on a webview .It will not work in iOS.

Workaround:

You can add a TapGestureRecognizer on the webview.And you have to implement it by using CustomRenderer.Because it will create conflict if you add TapGestureRecognizer in forms. Refer to the following code.

in Forms

public MainPage()
{
 if (Device.RuntimePlatform == "iOS")
   {

      MessagingCenter.Subscribe<Object,string>(this,"webview_click", (sender,arg)=> {

     // int index = Convert.ToInt16(arg));

     });
   }
}

in iOS

using System;
using Foundation;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
using xxx;
using xxx.iOS;
using ObjCRuntime;
[assembly:ExportRenderer(typeof(WebView),typeof(MyWebViewRenderer))]
namespace xxx.iOS
{
  public class MyWebViewRenderer : WebViewRenderer, IUIGestureRecognizerDelegate
  {

    public bool isFirstLoad = true;

    public MyWebViewRenderer()
    {

    }

    protected override void OnElementChanged(VisualElementChangedEventArgs e)
    {
        base.OnElementChanged(e);

        if (e != null)
        {
            UITapGestureRecognizer tap = new UITapGestureRecognizer(this, new Selector("Tap_Handle:"));
            tap.WeakDelegate = this;
            this.AddGestureRecognizer(tap);
        }

    }

    [Export("gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer:")]
    public bool ShouldRecognizeSimultaneously(UIGestureRecognizer gestureRecognizer, UIGestureRecognizer otherGestureRecognizer)
    {
        return true;
    }

    [Export("Tap_Handle:")]
    void Tap_Handle(UITapGestureRecognizer tap)
    {
        if(isFirstLoad)
        {
            isFirstLoad = false;
            MessagingCenter.Send<Object,string>(this, "webview_click",Element.AutomationId);
        }
    }

  }
}