Xamarin Android Javascript 和 C# 之间的两种通信方式 [英] Xamarin Android two way communication between Javascript and C#

问题描述

我正在使用 Xamarin Android 开发一个应用程序，它有一个显示网页的 WebView.我想实现从 WebView 到 C# 的 Javascript 之间的双向通信.我可以使用这个 link 从 Javascript 调用 C#.但是我找不到将数据从 C# 发送回 Javascript 的方法.有没有办法以这种方法来回发送数据.我认为用 Javascript 编写回调会起作用，但如何从 C# 代码中触发它.

I am developing an app using Xamarin Android which has a WebView displaying a web page. I want to implement a two way communication between Javascript from WebView to c#. I could call C# from Javascript using this link. However i couldn't find a way to send data back from C# to Javascript. Is there a way to send data back and forth in this approach. I thought writing a callback in Javascript would work but how to fire it from C# code.

现在，我的问题是如何从 javascript 接口类调用 WebView.我有一个 Javascript 接口类 https://developer.xamarin.com/食谱/android/controls/webview/call_csharp_from_javascript/命名空间扫描器Android{公共类 JSInterface:Java.Lang.Object{上下文上下文；WebView webView;

Now, My problem is how to call WebView from a javascript interface class. I have a Javascript interface class as mentioned https://developer.xamarin.com/recipes/android/controls/webview/call_csharp_from_javascript/ namespace ScannerAndroid { public class JSInterface: Java.Lang.Object { Context context; WebView webView;

    public JSInterface (Context context, WebView webView1)
    {
      this.context = context;
      this.webView = webView1;
    }

    [Export]
    [JavascriptInterface]
    public void ShowToast()
    {
      Toast.MakeText (context, "Hello from C#", ToastLength.Short).Show ();
      this.webView.LoadUrl ("javascript:callback('Hello from Android Native');");

    }   
  }
}

代码在 LoadUrl 行抛出异常.java.lang.Throwable:在线程Thread-891"上调用了 WebView 方法.所有 WebView 方法都必须在同一线程上调用.(预期的 Looper Looper (main, tid 1) {42ce58a0} 在 null 上调用，仅供参考，主要 Looper 是 Looper (main, tid 1) {42ce58a0})

The code throws an exception at LoadUrl line. java.lang.Throwable: A WebView method was called on thread 'Thread-891'. All WebView methods must be called on the same thread. (Expected Looper Looper (main, tid 1) {42ce58a0} called on null, FYI main Looper is Looper (main, tid 1) {42ce58a0})

现在我正在努力如何从这个 Java 脚本接口类中引用 WebView

Now i am struggling how to refer the WebView from this Java script interface class

推荐答案

是的.那是可能的.如果您的目标是 KitKat 或更高版本，则可以使用:

Yes. That is possible. If you are targeting KitKat or higher you can use:

webView.EvaluateJavascript("enable();", null);

在这种情况下 enable(); 是一个 JS 函数.

Where in this case enable(); is a JS function.

如果您的目标是较低的 API 级别，您可以使用 LoadUrl();:

If you are targeting lower API levels you can use LoadUrl();:

webView.LoadUrl("javascript:enable();");

您在 LoadUrl 上抱怨的错误是因为它出于某种原因发生在非 UI 线程上.

The error you get where it complains on LoadUrl is because it for some reason happens on a non-UI thread.

既然您已经将 Context 传递到您的 JavascriptInterface 类中，那么您可以简单地将 ShowToast 的内容包装在:

Since you have already passed on the Context into your JavascriptInterface class, then you can simply wrap the contents of ShowToast in:

context.RunOnUiThread(() => {
   // stuff here
});

只需将签名从 Context 更改为 Activity，它应该可以帮助您将您编组回 UI 线程.

Just change signature from Context to Activity and it should help you marshal you back on UI thread.

这篇关于Xamarin Android Javascript 和 C# 之间的两种通信方式的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！