解决WebView实现获得js中Function返回值

整理自：http://blog.sina.com.cn/s/blog_67ac56e70101ajlp.html

本文实现的是使用WebView调用js代码，并获得function的return值

1. 创建自定义的 MyWebView 并继承 WebView 

public class MyWebView extends WebView {


    public MyWebView(Context context) {
        super(context);

    }

    public MyWebView(Context context, AttributeSet attrs) {
        super(context, attrs);
        // TODO Auto-generated constructor stub
    }
    public MyWebView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        // TODO Auto-generated constructor stub
    }

    public String stringByEvaluatingJavaScriptFromString(String script) {
        if(Build.VERSION.SDK_INT>= Build.VERSION_CODES.JELLY_BEAN) {

            try{

                Field mp = WebView.class.getDeclaredField("mProvider");

                mp.setAccessible(true);

                Object webViewObject = mp.get(this);

                Field wc = webViewObject.getClass().getDeclaredField("mWebViewCore");

                wc.setAccessible(true);

                Object webViewCore = wc.get(webViewObject);

                Field bf = webViewCore.getClass().getDeclaredField("mBrowserFrame");

                bf.setAccessible(true);

                Object browserFrame = bf.get(webViewCore);

                Method stringByEvaluatingJavaScriptFromString = browserFrame.getClass()

                        .getDeclaredMethod("stringByEvaluatingJavaScriptFromString",

                                String.class);

                stringByEvaluatingJavaScriptFromString.setAccessible(true);

                Object obj_value = stringByEvaluatingJavaScriptFromString.invoke(

                        browserFrame, script);

                return String.valueOf(obj_value);

            }catch(Exception e) {
                e.printStackTrace();
                Log.e("!!!","stringByEvaluatingJavaScriptFromString", e);

            }

            return null;

        }else{

            try{

                Field[]fields= WebView.class.getDeclaredFields();

                //由webview取到webviewcore

                Field field_webviewcore = WebView.class.getDeclaredField("mWebViewCore");

                field_webviewcore.setAccessible(true);

                Object obj_webviewcore = field_webviewcore.get(this);

                //由webviewcore取到BrowserFrame

                Field field_BrowserFrame = obj_webviewcore.getClass().getDeclaredField(

                        "mBrowserFrame");

                field_BrowserFrame.setAccessible(true);

                Object obj_frame = field_BrowserFrame.get(obj_webviewcore);

                //获取BrowserFrame对象的stringByEvaluatingJavaScriptFromString方法

                Method method_stringByEvaluatingJavaScriptFromString = obj_frame.getClass()

                        .getMethod("stringByEvaluatingJavaScriptFromString", String.class);

                //执行stringByEvaluatingJavaScriptFromString方法

                Object obj_value = method_stringByEvaluatingJavaScriptFromString.invoke(

                        obj_frame,

                        script);

                //返回执行结果

                return String.valueOf(obj_value);

            }catch(Exception e) {
                e.printStackTrace();
                Log.e("!!!","stringByEvaluatingJavaScriptFromString", e);

            }

            return null;

        }

    }


}

2. 使用

（a）加载页面 ：webView.loadUrl("file:///android_asset/www/test.html"); 

（b）运行js：

(1)旧的方法，不能获得return值：webView.loadUrl("javascript:fun()"); 

        (2)新的方法，不能获得return值：

Toast.makeText(TestActivity.this,webView.stringByEvaluatingJavaScriptFromString("javascript:fun()"),Toast.LENGTH_LONG).show();

  (c)获得var值

Toast.makeText(TestActivity.this,webView.stringByEvaluatingJavaScriptFromString("varName"),Toast.LENGTH_LONG).show();

例子代码：http://download.youkuaiyun.com/detail/qqgrid/8210305