WebView 에서 JavaScript 실행은 간단히 아래와 같히 펑션을 호출하면 된다.

this.webView.Eval("TestFunction()");

 

하지만 리턴이 있는 JavaSecript funtion 실행결과는 저 형태로는 안된다.

따로 Renderer 를 이용해 구현하는 방법을 소개한다.

 

먼저 .Net Standard 프로젝트에 아래와 같이 WebViewer 를 만든다.

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;

namespace Test
{
    public class WebViewer : WebView
    {
        public static BindableProperty EvaluateJavascriptProperty =
        BindableProperty.Create(nameof(EvaluateJavascript), typeof(Func<string, Task<string>>), typeof(WebViewer), null, BindingMode.OneWayToSource);

        public Func<string, Task<string>> EvaluateJavascript
        {
            get { return (Func<string, Task<string>>)GetValue(EvaluateJavascriptProperty); }
            set { SetValue(EvaluateJavascriptProperty, value); }
        }
    }
}

이제 위 항목을 상속받아서 각 기기별로 Renderer 를 생성하자.

 

Android

using System;
using System.Threading;
using System.Threading.Tasks;
using Android.Content;
using Android.Webkit;
using Test;
using Test.Droid;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;

[assembly: ExportRenderer(typeof(WebViewer), typeof(WebViewRender))]
namespace Test.Droid
{
    public class WebViewRender : WebViewRenderer
    {
        public WebViewRender(Context context) : base(context)
        { }

        protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.WebView> e)
        {
            base.OnElementChanged(e);

            if (e.NewElement is WebViewer webView)
            {
                webView.EvaluateJavascript = async (js) =>
                {
                    var reset = new ManualResetEvent(false);
                    var response = string.Empty;
                    Device.BeginInvokeOnMainThread(() =>
                    {
                        Control?.EvaluateJavascript(js, new JavascriptCallback((r) => { response = r; reset.Set(); }));
                    });
                    await Task.Run(() => { reset.WaitOne(); });
                    return response;
                };
            }
        }
    }

    internal class JavascriptCallback : Java.Lang.Object, IValueCallback
    {
        public JavascriptCallback(Action<string> callback)
        {
            _callback = callback;
        }

        private Action<string> _callback;
        public void OnReceiveValue(Java.Lang.Object value)
        {
            _callback?.Invoke(Convert.ToString(value));
        }
    }
}

 

iOS

using System.Threading.Tasks;
using Test;
using Test.iOS;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;

[assembly: ExportRenderer(typeof(WebViewer), typeof(WebViewRender))]
namespace Test.iOS
{
    public class WebViewRender : WebViewRenderer
    {
        protected override void OnElementChanged(VisualElementChangedEventArgs e)
        {
            base.OnElementChanged(e);

            if (e.NewElement is WebViewer webView)
            {
                webView.EvaluateJavascript = (js) =>
                {
                    return Task.FromResult(this.EvaluateJavascript(js));
                };
            }
        }
    }
}

 

UWP

using System;
using Test;
using Test.UWP;
using Xamarin.Forms;
using Xamarin.Forms.Platform.UWP;

[assembly: ExportRenderer(typeof(WebViewer), typeof(WebViewRender))]
namespace Test.UWP
{
    public class WebViewRender : WebViewRenderer
    {
        protected override void OnElementChanged(ElementChangedEventArgs<WebView> e)
        {
            base.OnElementChanged(e);
            if (e.NewElement is WebViewer webView)
            {
                webView.EvaluateJavascript = async (js) =>
                {
                    return await Control.InvokeScriptAsync("eval", new[] { js });
                };
            }
        }
    }
}

 

이제 화면에서 아래와 같이 컨트롤을 넣고

<test:WebViewer x:Name="webView" HorizontalOptions="FillAndExpand"  VerticalOptions="FillAndExpand"/>

아래와 같이 코딩하면 function 의 결과 값을 받아올수 있다.

var result = await this.webView.EvaluateJavascript("GetTest();");

 

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