今天调查一个线上Bug，发现是
webView中的一小段
javascript，会直接调用到后台APK的一个
java事件，最后导致
java中nullpointexception。
感兴趣的是，WebView中的
javascript如何调用APK中的
java方法。
一个例子：
通过JS取得
Android的GPS数据
第一步，WebKit的准备
首先，给与WebKit的
javascript的执行许可
[
java]
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
WebView wv = new WebView(this);
wv.getSettings().set
javaScriptEnabled(true);//JS利用OK
setContentView(wv);
}
然后，塞入自己的
javascript拦截器
[
java]
JsObj jo = new JsObj(this);
wv.add
javascript
interface(jo, "roid");
第二步，定义自己的
javascript拦截器
[
java]
class JsObj {
private Context con;
public JsObj(Context con) {
this.con = con;
}
public String gps(String top, String end) {
LocationManager locman = (LocationManager)
con.getSystemService(Context.LOCATION_SERVICE);
Location loc = locman.getCurrentLocation("gps");
int lat = (int) (loc.getLatitude() * 1000000);
int lon = (int) (loc.getLongitude() * 1000000);
return top + "緯度:" + lat + ", 経度: " + lon + end;
}
}
第三步，定义一个可运行的html
[html]
<html>
<head><title>JS calls
Android Method</title></head>
<body>
<h1>JS on
Android</h1>
<script type="text/
javascript">
document.write(roid.gps("<i>", "</i>"));
</script>
</body>
</html>
在这个代码里面，可以用roid.gps的方法调用第二步定义的
java函数
最后，全部的代码
[
java]
package com.adamrocker.
Android.web;
import
Android.app.Activity;
import
Android.content.Context;
import
Android.location.Location;
import
Android.location.LocationManager;
import
Android.os.Bundle;
import
Android.webkit.WebView;
public class WebkitTest extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
WebView wv = new WebView(this);
wv.getSettings().set
javaScriptEnabled(true);
JsObj jo = new JsObj(this);
wv.add
javascriptInterface(jo, "roid");
setContentView(wv);
wv.loadUrl("www.at
cpu.com");
}
class JsObj {
private Context con;
public JsObj(Context con) {
this.con = con;
}
public String gps(String top, String end) {
LocationManager locman = (LocationManager) con
.getSystemService(Context.LOCATION_SERVICE);
Location loc = locman.getCurrentLocation("gps");
int lat = (int) (loc.getLatitude() * 1000000);
int lon = (int) (loc.getLongitude() * 1000000);
return top + "緯度:" + lat + ", 経度: " + lon + end;
}
}
}
未完
我还想知道为什么，在webview里面定义一个JSObject，就可以连接
javascript和后台函数
他们之间是如何通信的？
我稍微调查了一下WebView的底层代码，webview初期化的时候
[
java]
/* Initialize private data within the WebCore thread.
*/
private void [More ...] initialize() {
/* Initialize our private BrowserFrame class to handle all
* frame-related functions. We need to create a new view which
* in turn creates a C level FrameView and attaches it to the frame.
*/
mBrowserFrame = new BrowserFrame(mContext, this, mCallbackProxy,
mSettings, m
javascriptInterfaces);
m
javascriptInterfaces = null;
// Sync the native settings and also create the WebCore thread handler.
mSettings.syncSettingsAndCreateHandler(mBrowserFrame);
// Create the handler and transfer messages for the IconDatabase
WebIconDatabase.getInstance().createHandler();
// Create the handler for WebStorage
WebStorage.getInstance().createHandler();
// Create the handler for GeolocationPermissions.
GeolocationPermissions.getInstance().createHandler();
// The transferMessages call will transfer all pending messages to the
// WebCore thread handler.
mEventHub.transferMessages();
// Send a message back to WebView to tell it that we have set up the
// WebCore thread.
if (mWebView != null) {
Message.obtain(mWebView.mPrivateHandler,
WebView.WEBCORE_INITIALIZED_MSG_ID,
mNativeClass, 0).sendToTarget();
}
}
生成了显示用对象
mBrowserFrame
而此对象的所有操作事件，都会被
mEventHub截获
而mEventHub会将请求发送给真正需要处理的MessageStub。 通过messageName
[
java]
Transfer all messages to the newly created webcore thread handler.
private void [More ...] transferMessages() {
mTid = Process.myTid();
mSavedPriority = Process.getThreadPriority(mTid);
mHandler = new Handler() {
@Override
public void [More ...] handleMessage(Message msg) {
if (DebugFlags.WEB_VIEW_CORE) {
Log.v(LOGTAG, (msg.what < REQUEST_LABEL
|| msg.what
> VALID_NODE_BOUNDS ? Integer.toString(msg.what)
: HandlerDebugString[msg.what
- REQUEST_LABEL])
+ " arg1=" + msg.arg1 + " arg2=" + msg.arg2
+ " obj=" + msg.obj);
}
switch (msg.what) {
case WEBKIT_DRAW:
webkitDraw();
作者：nanjingjiangbiao
