xamarin.forms webview.focus事件在Android上引发，但在iOS上没有

Question

我正在使用Xamarin.Forms网格应用程序在网格CardGrid的单元格中将几个html元素显示为WebView：

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() 创建 html 代码片段。

RenderingCard() 在网格单元内创建 WebView。

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);
}

我想捕获焦点事件，当用户点击卡片(WebView)并使用AutomationId获取卡片的索引(html代码片段)时：

private void Card_Tapped(object sender, EventArgs e)
{
WebView card = (WebView)sender;
int index = Convert.ToInt16(card.AutomationId));
}

这适用于安卓。在 iOS 下，永远不会引发该事件。有什么解决方案的想法吗？

Answer 1

原因：

表单中Focus的属性对应于我们在本机iOS平台中称为成为FirstResponder的方法。不幸的是，UIWebView和WKwebview不支持该方法becomeFirstResponder。此方法仅在某些"输入控件"中可用，例如UITextField和UITextView(Entry in Forms)。因此，即使您将事件设置为webview.它将无法在iOS中工作。

解决方法：

您可以在 Web 视图上添加TapGestureRecognizer。您必须使用 CustomRenderer 来实现它。因为如果在窗体中添加 TapGestureRecognizer，它会产生冲突。 请参考以下代码。

在表单中

public MainPage()
{
if (Device.RuntimePlatform == "iOS")
{
MessagingCenter.Subscribe<Object,string>(this,"webview_click", (sender,arg)=> {
// int index = Convert.ToInt16(arg));
});
}
}

在 iOS 中

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);
}
}
}
}