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Android与javaScript的交互

WebView与js的交互包含两方面,一是在html中通过js调用java代码；二是在安卓java代码中调用js。

一、html中通过js调用java代码

js中调用java代码其实就记住一点，WebView设置一个和js交互的接口（这里的接口是一般的意思，不是java中接口的含义），这个接口其实就是一个一般的类，同时为这个接口取一个别名。这个过程如下：
mWebView.addJavaScriptInterface(new DemoJavaScriptInterface(),"demo");
new DemoJavaScriptInterface()就是这个接口，demo就是这个接口的别名。
上面的代码执行后在html中js就能通过别名（这里是“demo”）来调用DemoJavaScriptInterface类中的任何方法了。
如果我们想让html中的一个button点击之后调用java中的函数可以这样：
<input type="button" value="click me" onclick="window.demo.clickOnAndroid()"/>
但是因为安全问题，在Android4.2中（如果应用的android:targetSdkVersion为17+）JS只能访问带有@javaScriptInterface注解的java函数，所以开发版本较高的时候，在需要被调用的函数前加上这个注解。4.2以下为了安全尽量不要调用addJavascriptInterface，需要另谋他法。

下面是google官方给的实例：
WebViewDemo.java

[代码]java代码：

package com.google.android.webviewdemo;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.webkit.JsResult;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebView;
/**
 * Demonstrates how to embed a WebView in your activity. Also demonstrates how
 * to have javascript in the WebView call into the activity, and how the activity
 * can invoke javascript.
 * <p>
 * In this example, clicking on the android in the WebView will result in a call into
 * the activities code in {@link DemoJavaScriptInterface#clickOnAndroid()}. This code
 * will turn around and invoke javascript using the {@link WebView#loadUrl(String)}
 * method.
 * </p><p>
 * Obviously all of this could have been accomplished without calling into the activity
 * and then back into javascript, but this code is intended to show how to set up the
 * code paths for this sort of communication.
 *
 */
public class WebViewDemo extends Activity {
    private static final String LOG_TAG = "WebViewDemo";
    private WebView mWebView;
    private Handler mHandler = new Handler();
    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        setContentView(R.layout.main);
        mWebView = (WebView) findViewById(R.id.webview);
        WebSettings webSettings = mWebView.getSettings();
        webSettings.setSavePassword(false);
        webSettings.setSaveFormData(false);
        webSettings.setJavaScriptEnabled(true);
        webSettings.setSupportZoom(false);
        mWebView.setWebChromeClient(new MyWebChromeClient());
        mWebView.addJavascriptInterface(new DemoJavaScriptInterface(), "demo");
        mWebView.loadUrl("file:///android_asset/demo.html");
    }
    final class DemoJavaScriptInterface {
        DemoJavaScriptInterface() {
        }
        /**
         * This is not called on the UI thread. Post a runnable to invoke
         * loadUrl on the UI thread.
         */
        public void clickOnAndroid() {
            mHandler.post(new Runnable() {
                public void run() {
                    mWebView.loadUrl("javascript:wave()");
                }
            });
        }
    }
    /**
     * Provides a hook for calling "alert" from javascript. Useful for
     * debugging your javascript.
     */
    final class MyWebChromeClient extends WebChromeClient {
        @Override
        public boolean onJsAlert(WebView view, String url, String message, JsResult result) {
            Log.d(LOG_TAG, message);
            result.confirm();
            return true;
        }
    }
}</p>

demo.html

[代码]xml代码：

<html>
    <script language="javascript">
        /* This function is invoked by the activity */
        function wave() {
            alert("1");
            document.getElementById("droid").src="android_waving.png";
            alert("2");
        }
    </script>
    <body>
        <!-- Calls into the javascript interface for the activity -->
        <a onClick="window.demo.clickOnAndroid()">
            <div style="80px;
                margin:0px auto;
                padding:10px;
                text-align:center;
                border:2px solid #202020;" >
                <img id="droid" src="android_normal.png"/><br>
                Click me!
            </div>
        </a>
    </body>
</html>

main.xml

[代码]xml代码：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/intro"
        android:padding="4dip"
        android:textSize="16sp"
        />
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
    <WebView
        android:id="@+id/webview"
        android:layout_width="fill_parent"
        android:layout_height="0dip"
        android:layout_weight="1"
        />
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
</LinearLayout>

Android调用js

调用webview页面内的js方法,调用形式：
mWebView.loadUrl("javascript:wave()");
其中wave()是js中的一个方法，当然你可以把这个方法改成其他的方法，也就是android调用其他的方法。但java不能直接获取Js方法的返回结果。

小结

具体交互流程如下：

点击图片，则在js端直接调用android上的方法clickOnAndroid()；
clickOnAndroid()方法（利用线程）调用js的方法。
被调用的js直接控制html。

利用webView的这种方式在有些时候UI布局就可以转成相应的html代码编写了，而html布局样式之类有DW这样强大的工具，而且网上很多源码，很多代码片。在UI和视觉效果上就会节省很多时间，重复发明轮子没有任何意义。

交互结果

Android Webview中Java调用Js方法很容易，loadUrl("javascript:isOk()")就可以调用isOk这个Js方法，但不能直接获取Js方法的返回结果。
1.传统的方法中，Js获取Java信息可以采用如下方式：

[代码]java代码：

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class JsObject {
      @JavascriptInterface
      public String toString() { return "injectedObject"; }
   }
webView.addJavascriptInterface(new JsObject(), "injectedObject");
webView.loadData("", "text/html", null);
webView.loadUrl("javascript:alert(injectedObject.toString())");

2.Java获取Js信息（如通过Js获取网页源代码）可以这样：

[代码]java代码：

import android.app.Activity;
import android.graphics.Bitmap;
import android.os.Bundle;
import android.util.Log;
import android.webkit.WebView;
import android.webkit.WebViewClient;
 
public class HtmlSource extends Activity {
    private WebView webView;
 
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        webView = (WebView)findViewById(R.id.webview);
        webView.getSettings().setJavaScriptEnabled(true);
        webView.addJavascriptInterface(new InJavaScriptLocalObj(), "local_obj");
        webView.setWebViewClient(new MyWebViewClient());
        webView.loadUrl("http://www.cnblogs.com/hibraincol/");
    }
 
 
   final class MyWebViewClient extends WebViewClient{  
        public boolean shouldOverrideUrlLoading(WebView view, String url) {   
            view.loadUrl(url);   
            return true;   
        }  
        public void onPageStarted(WebView view, String url, Bitmap favicon) {
            Log.d("WebView","onPageStarted");
            super.onPageStarted(view, url, favicon);
        }    
        public void onPageFinished(WebView view, String url) {
            Log.d("WebView","onPageFinished ");
            view.loadUrl("javascript:window.local_obj.showSource(''+" +
                "document.getElementsByTagName('html')[0].innerHTML+'');");
            super.onPageFinished(view, url);
        }
    }
 
    final class InJavaScriptLocalObj {
 
        public void showSource(String html) {
            Log.d("HTML", html);
        }
    }
}

当网页中有超链接跳转时，将会调用WebClient的shouldOverrideUrlLoading方法，若设置 WebViewClient 且该方法返回 true，则说明由应用的代码处理该 url，WebView 不处理，就可以达到拦截跳转的效果。

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原文地址：https://www.cnblogs.com/android-blogs/p/5759929.html