Android（五十七）：WebView - 获取网页logo和标题、监听页面滚动、刷新页面、两端交互

    
    
    
    
    
    
    
    



    
    交互
    

using Android.App;
using Android.Content;
using Android.Graphics;
using Android.OS;
using Android.Views;
using Android.Webkit;
using Android.Widget;
using Java.Interop;
using Java.Lang;

namespace PrimaryBlankApp
{
    [Activity(Label = "@string/app_name", Theme = "@style/AppTheme", MainLauncher = true)]
    public class MainActivity : Activity
    {
        public static ImageView IconView;
        public static TextView TitleView;
        private WebView _webView;
        private long _exitTime;

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.activity_main);

            IconView = FindViewById(Resource.Id.icon);
            TitleView = FindViewById(Resource.Id.title);
            var refresh = FindViewById(Resource.Id.refresh);
            var jsBtn = FindViewById(Resource.Id.js_btn);
            var contentLayout = FindViewById(Resource.Id.content_layout);

            _webView = new WebView(this);
            _webView.LayoutParameters =
                new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MatchParent, ViewGroup.LayoutParams.MatchParent);
            _webView.SetWebChromeClient(new MyWebChromeClient());
            _webView.Settings!.JavascriptEnabled = true; // 运行执行js脚本
            // 必须，参数一为供前端使用的对象Value（仅暴露的），参数二为供前端使用的对象Key
            _webView.AddJavascriptInterface(new JavascriptMethod(this), "Android"); 
            _webView.LoadUrl("http://10.10.1.184:5500/");

            contentLayout?.AddView(_webView);

            // 监听WebView滚动
            _webView.ScrollChange += (sender, args) => { JavascriptMethod.ShowToast($"监听网页滚动 ---> {args.ScrollY}"); };

            // 刷新
            if (refresh != null)
                refresh.Click += delegate { _webView.Reload(); };

            // 调js
            if (jsBtn != null)
                jsBtn.Click += delegate { _webView.LoadUrl("javascript:handleAndroidFun()"); };
        }

        // 返回键
        public override void OnBackPressed()
        {
            // 判断网页是否能后退，可以则后退
            if (_webView.CanGoBack())
                _webView.GoBack();
            // 网页不能后退,则连续点击两次间隔不超过2000退出App
            else
            {
                if (JavaSystem.CurrentTimeMillis() - _exitTime > 2000)
                {
                    Toast.MakeText(this, "再按一次退出程序", ToastLength.Short)?.Show();
                    _exitTime = JavaSystem.CurrentTimeMillis();
                }
                else
                    base.OnBackPressed();
            }
        }

        // 前端的方法类
        private class JavascriptMethod : Object
        {
            private static Context _context;

            public JavascriptMethod(Context context)
            {
                _context = context;
            }

            // 需要引入 Mono.Android.Export.dll
            [Export("ShowToast")] // 暴露给前端的方法名称
            [JavascriptInterface] // 将方法暴露给前端
            public static string ShowToast(string str)
            {
                Toast.MakeText(_context, str, ToastLength.Short)?.Show();
                return str;
            }
        }
    }

    internal class MyWebChromeClient : WebChromeClient
    {
        public override void OnReceivedIcon(WebView view, Bitmap icon)
        {
            MainActivity.IconView.SetImageBitmap(icon);
            base.OnReceivedIcon(view, icon);
        }

        public override void OnReceivedTitle(WebView view, string title)
        {
            MainActivity.TitleView.Text = title;
            base.OnReceivedTitle(view, title);
        }
    }
}