Android中JavaScript与Java交互

在4.2以前，JavaScript与Java交互如下：

webview.getSetting().setJavaScriptEnable(true);webview.addJavascriptInterface(new Object(){            public void clickOnAndroid(){                 handler.post(new Runnable() {                    @Override                    public void run() {                        System.err.println("javascript 调用 java");                    }                });             }         }, "javascript对象");

在4.2以后，为了使JavaScript能够调用Java的方法，需要为向JavaScript暴露的Java方法添加@JavascriptInteface 注解。否则在targetSdkVersion 17以上的版本，将会报错：
E/Web Console:Uncaught Type Error:Object [object Object] has no method ‘clickOnAndroid’

 webview.addJavascriptInterface(new Object(){             @JavascriptInterface            public void clickOnAndroid(){                 handler.post(new Runnable() {                    @Override                    public void run() {                        System.err.println("javascript 调用 java");                    }                });             }         }, "javascript对象");

简单案例：

package com.example.webviewdemo;@SuppressLint("SetJavaScriptEnabled")public class MainActivity extends Activity {    private WebView webview;    private Handler handler;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        initView();    }    private void initView() {        webview = (WebView) findViewById(R.id.webview);        WebSettings settings = webview.getSettings();        settings.setJavaScriptEnabled(true);         handler = new Handler();         webview.addJavascriptInterface(new Object(){             @JavascriptInterface            public void clickOnAndroid(){                 handler.post(new Runnable() {                    @Override                    public void run() {                        webview.loadUrl("javascript:testJS()");                    }                });             }         }, "demo");        webview.loadUrl("file:///android_asset/demo.html");    }}

js代码(放在assets目录下)：

<html><script language="javascript"> function testJS() { document.getElementById("myPic").src="test.png"; } </script><body>  <a onClick="window.demo.clickOnAndroid()">  <img id="myPic" src="ic_launcher.png" mce_src="ic_launcher.png"/><br>切换</a></body></html>

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