Xamarin WebView - Call C# Method

问题

Is there a way in Xamarin's WebView that allows me to attach javascript events to my html elements and call C# method.

I could easily do this in Android by using JavaScriptInterface

<video width="320" height="240" controls="controls" poster='poster.gif'
       onclick="window.JSInterface.startVideo('file:///sdcard/test.3gp');"

How would I manage to this in Xamarin

回答1:

Create a JavaScript Interface Class

Create a C# class that contains methods to be called from JavaScript. If you are targeting Android API level 17 or later, this JavaScript-to-C# interface class must annotate each JavaScript-callable method with [JavascriptInterface] and [Export] as shown in the following example. If you are targeting Android API Level 16 or earlier, this interface class must implement Java.Lang.IRunnable as explained in Android API Level 16 and Earlier (later in this recipe):

• Create a C# class that is derived from Java.Lang.Object. In the following example, we name our class MyJSInterface and implement a method to display a toast when it is called from JavaScript:

    public  class MyJSInterface : Java.Lang.Object
    {
        Context context;
        public MyJSInterface (Context context)
        {
            this.context = context;
        }
            public void ShowToast ()
            {
                Toast.MakeText (context, "Hello from C#", ToastLength.Short).Show ();
            }
    }
  

• Annotate each method that is to be exposed to JavaScript with [Export] and [JavascriptInterface] (see IJavascriptInterface for more information about the JavascriptInterface annotation). In the following example, the ShowToast method is annotated so that it can be called from JavaScript. Note that you must include the Java.Interop and Android.Webkit using statements as shown in this example:

  using Java.Interop;
  using Android.Webkit;
  ...
  [Export]
  [JavascriptInterface]
  public void ShowToast ()
  {
      Toast.MakeText(context, "Hello from C#", ToastLength.Short).Show();
  }
  

• Add a project reference to Mono.Android.Export (so you can use the [Export] annotation):

  1.In Visual Studio, right-click References in the Solution Explorer and select Add Reference.... In Xamarin Studio, right-click References in the Solution Pad and select Edit References....

  2.In the search field, enter Mono.Android.Export. When you have located it, enable the check mark next to it and click OK.

---

Refer :

• http://dotnetthoughts.net/how-to-invoke-c-from-javascript-in-android/
• https://developer.xamarin.com/recipes/android/controls/webview/call_csharp_from_javascript/
• https://developer.xamarin.com/samples/monodroid/WebViewJavaScriptInterface/
• https://developer.xamarin.com/api/type/Android.Webkit.JavascriptInterface/

来源：https://stackoverflow.com/questions/37930626/xamarin-webview-call-c-sharp-method