Crosswalk入门

Crosswalk入门

• CSDN资讯：Crosswalk的介绍
• Crosswalk官方地址

上面的链接可以看到Crosswalk的介绍，Crosswalk种种吹牛逼的描述我就不写了。写一下我的使用感受：

1. 不用费力搞什么自己封装了，直接像用WebView一样使用。      在使用android-chromium这个库时，不仅要自己封装API来方便使用，还要操心Chromium的初始化，甚至还需要在清单文件里写一堆关于Chromium的东西，用来帮助Chromium建立单独的进程（Crosswalk只会创建Chromium的线程，不需要独立进程）。
2. Crosswalk由组织维护，比个人维护强多了。
3. 跟随最新的Chromium不断更新，js等不用担心有函数没法使用。而且不断更新过程中，肯定也会修复以前存在的bug，稳定性也是不用担心的。

最新稳定版Crosswalk基于Chromium38编译。

注：此库也可以配合Cordova(PhoneGap)使用。

OK，感受说完，上教程。

集成到应用中

1. 下载zip包，解压后导入。
2. 关联此Library。

3. 在清单文件中写入下列权限

   <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
   <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
   <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
   <uses-permission android:name="android.permission.CAMERA" />
   <uses-permission android:name="android.permission.INTERNET" />
   <uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS" />
   <uses-permission android:name="android.permission.RECORD_AUDIO" />
   <uses-permission android:name="android.permission.WAKE_LOCK" />
   <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

   注：使用过程中，观察Logcat可以看到报需要蓝牙权限，可以不用管它，不添加蓝牙权限可以正常使用。此外，使用XWalkView必须开启硬件加速。

   XWalkView needs hardware acceleration to render web pages. As a result, the AndroidManifest.xml of the caller's app must be appended with the attribute "android:hardwareAccelerated" and its value must be set as "true".

   android:hardwareAccelerated : The default value is "true" if you've set either minSdkVersion or targetSdkVersion to "14" or higher; otherwise, it's "false".

   在清单文件Application中声明即可。

   <application android:name="android.app.Application" android:label="XWalkUsers"
    android:hardwareAccelerated="true">

基本使用

Crosswalk中用来替代WebView的控件叫XWalkView。

layout文件写法

和其他自定义控件一样。

<org.xwalk.core.XWalkView android:id="@+id/activity_main"
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent">
</org.xwalk.core.XWalkView>

代码中使用

重中之重：防止内存泄漏

和其他Android的控件不同，这个类需要监听系统事件。例如：生命周期、intent、Activity result。

控件内置的Web引擎需要获取并处理这些信息。并且当XWalkView 不再需要使用的时候，在onDestroy方法中XWalkView必须显式的调用destroy方法，否则容易造成Web引擎的内存泄漏。

原文如下：

Unlike other Android views, this class has to listen to system events like application life cycle, intents, and activity result. The web engine inside this view need to get and handle them. And the onDestroy() method of XWalkView MUST be called explicitly when an XWalkView won't be used anymore, otherwise it will cause the memory leak from the native side of the web engine. It's similar to the destroy() method of Android WebView.

这段文字来自XWalkView官方API文档。奇怪的是官方的范例中并没有在意这些事情，直接像WebView一样使用，更没有使用destroy方法。考虑到之前使用android-chromium库也是需要显式调用。这里还是加上，避免内存泄漏。

   import android.app.Activity;
   import android.os.Bundle;

   import org.xwalk.core.XWalkView;

   public class MyActivity extends Activity {
     private XWalkView mXWalkView;
     @Override
     protected void onCreate(Bundle savedInstanceState) {
   		super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mXWalkView = (XWalkView) findViewById(R.id.activity_main);
    mXWalkView.load("http://crosswalk-project.org/", null);
     }

     @Override
     protected void onPause() {
       super.onPause();
       if (mXWalkView != null) {
         mXWalkView.pauseTimers();
         mXWalkView.onHide();
       }
     }

     @Override
     protected void onResume() {
       super.onResume();
       if (mXWalkView != null) {
         mXWalkView.resumeTimers();
         mXWalkView.onShow();
       }
     }

     @Override
     protected void onDestroy() {
       super.onDestroy();
       if (mXWalkView != null) {
         mXWalkView.onDestroy();
       }
     }

     @Override
     protected void onActivityResult(int requestCode, int resultCode, Intent data) {
       if (mXWalkView != null) {
         mXWalkView.onActivityResult(requestCode, resultCode, data);
       }
     }

     @Override
     protected void onNewIntent(Intent intent) {
       if (mXWalkView != null) {
         mXWalkView.onNewIntent(intent);
       }
     }
   }

loadUrl去哪了？

上面的代码中其实已经剧透了，使用load方法即可。

// url
mXWalkView.load("http://crosswalk-project.org/", null);

// this loads a file from the assets/ directory
mXWalkView.load("file:///android_asset/index.html", null);

public void load (String url, String content)

Load a web page/app from a given base URL or a content. If url is null or empty and content is null or empty, then this function will do nothing. If content is not null, load the web page/app from the content. If content is not null and the url is not set, return "about:blank" ifi calling getUrl(). If content is null, try to load the content from the url. It supports URL schemes like 'http:', 'https:' and 'file:'. It can also load files from Android assets, e.g. '        file:///android_asset/ '.

Parameters

url the url for web page/app.

content the content for the web page/app. Could be empty.

WebViewClient？

对应WebView的WebViewClient，XWalkView中有XWalkResourceClient。

mXWalkView.setResourceClient(new XWalkResourceClient(mXWalkView){
  @Override
  public void onLoadFinished(XWalkView view, String url) {
    super.onLoadFinished(view, url);
  }
  @Override
  public void onLoadStarted(XWalkView view, String url) {
    super.onLoadStarted(view, url);
  }
});

调用JavaScript

mXWalkView = (XWalkView) findViewById(R.id.activity_main);
XWalkSettings webSettings = mXWalkView.getSettings();
//Tells the WebView to enable JavaScript execution.
webSettings.setJavaScriptEnabled(true);

执行js

mXWalkView.load("javascript:document.body.contentEditable=true;", null);

当然，按照Kitcat引入的方式，使用evaluateJavascript方法也是可以的。（大神们推荐）

JavaScript回调Java

1. 定义js回调接口

   public class JsInterface {
     public JsInterface() {
     }
     @JavascriptInterface
     public String sayHello() {
       return "Hello World!";
     }
   }

   Caution: If you've set your targetSdkVersion to 17 or higher, you must add the @JavascriptInterface annotation to any method that you want available to your JavaScript (the method must also be public). If you do not provide the annotation, the method is not accessible by your web page when running on Android 4.2 or higher.From developer.android.com

   备注：这里的        @JavaScriptInterface 所在的包是        import org.xwalk.core.JavascriptInterface;

2. XWalkView设置JavaScript可用且绑定对象

   mXWalkView = (XWalkView) findViewById(R.id.activity_main);
   XWalkSettings webSettings = mXWalkView.getSettings();
   //Tells the WebView to enable JavaScript execution.
   webSettings.setJavaScriptEnabled(true);
   //绑定
   mXWalkView.addJavascriptInterface(new JsInterface(), "NativeInterface");

3. 调用html执行JavaScript或直接执行Javascript调用Java

   mXWalkView.load("file:///android_asset/index.html", null);

   index.html源码：

   <a href="#" onclick="clicked()">Say Hello</a>
   <script>
   function clicked() {
     alert(NativeInterface.sayHello());
   }
   </script>

高级使用

调试

Kitcat开始，Android提供了和Chrome联调功能。可以很方便的在Chrome中调试WebView中的代码。

Crosswalk使用Chromium内核当然也具备这个功能。

开启调试的语句如下：

  // turn on debugging
    XWalkPreferences.setValue(XWalkPreferences.REMOTE_DEBUGGING, true);

对于Crosswalk来说，这个设置是全局的。

使用动画或者设置隐藏可见注意

默认XWalkView不能使用动画，甚至setVisibility也不行。

XWalkView represents an Android view for web apps/pages. Thus most of attributes for Android view are valid for this class. Since it internally uses android.view.SurfaceView for rendering web pages by default, it can't be resized, rotated, transformed and animated due to the limitations of SurfaceView. Alternatively, if the preference key ANIMATABLE_XWALK_VIEW is set to True, XWalkView can be transformed and animated because TextureView is intentionally used to render web pages for animation support. Besides, XWalkView won't be rendered if it's invisible.

开启动画模式：

@Override
protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);

  // ANIMATABLE_XWALK_VIEW preference key MUST be set before XWalkView creation.
  XWalkPreferences.setValue(XWalkPreferences.ANIMATABLE_XWALK_VIEW, true);

  setContentView(R.layout.animatable_xwview_layout);
}
@Override
public void onDestroy() {
  super.onDestroy();

  // Reset the preference for animatable XWalkView.
  XWalkPreferences.setValue(XWalkPreferences.ANIMATABLE_XWALK_VIEW, false);
}

由于设置也像调试一样是全局的，在onDestroy时记得关闭。

暂停JS timer

html代码

<!DOCTYPE html>
<html>
<body>

<p>A script on this page starts this clock:</p>
<p id="demo"></p>

<script>
  var myVar = setInterval(function(){ myTimer(); }, 1000);

  function myTimer()
  {
    var d = new Date();
    var t = d.toLocaleTimeString();
    document.getElementById("demo").innerHTML = t;
  }
</script>

</body>
</html>

XWalkView对应方法：

mButton.setOnClickListener(new OnClickListener() {
  @Override
  public void onClick(View v) {
    if (mXWalkView != null) {
      if (!isPaused) {
        // Pause JS timer
        mXWalkView.pauseTimers();
        isPaused = true;
        mButton.setImageResource(android.R.drawable.ic_media_play);
      } else {
        // Resume JS timer
        mXWalkView.resumeTimers();
        isPaused = false;
        mButton.setImageResource(android.R.drawable.ic_media_pause);
      }
    }
  }
});

这也在防止内存泄漏，监听系统事件示例代码中提到过：

@Override
protected void onPause() {
   super.onPause();
   if (mXWalkView != null) {
     mXWalkView.pauseTimers();
     mXWalkView.onHide();
   }
}

@Override
protected void onResume() {
   super.onResume();
   if (mXWalkView != null) {
     mXWalkView.resumeTimers();
     mXWalkView.onShow();
   }
}

历史记录

mPrevButton.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick(View v) {
  // Go backward
  if (mXWalkView != null &&
    mXWalkView.getNavigationHistory().canGoBack()) {
      mXWalkView.getNavigationHistory().navigate(
        XWalkNavigationHistory.Direction.BACKWARD, 1);
  }
  XWalkNavigationItem navigationItem = mXWalkView.getNavigationHistory().getCurrentItem();
  showNavigationItemInfo(navigationItem);
    }
});

mNextButton.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick(View v) {
  // Go forward
  if (mXWalkView != null &&
    mXWalkView.getNavigationHistory().canGoForward()) {
      mXWalkView.getNavigationHistory().navigate(
        XWalkNavigationHistory.Direction.FORWARD, 1);
  }
  XWalkNavigationItem navigationItem = mXWalkView.getNavigationHistory().getCurrentItem();
  showNavigationItemInfo(navigationItem);
    }
});

private void showNavigationItemInfo(XWalkNavigationItem navigationItem){
    url = navigationItem.getUrl();// Get the url of current navigation item.
    originalUrl = navigationItem.getOriginalUrl();// Get the original url of current navigation item
    title = navigationItem.getTitle();

    text1.setText(title);
    text2.setText(url);
    text3.setText(originalUrl);
}

自动视频暂停

// The web page below will display a video.
// When home button is pressed, the activity will be in background, and the video will be paused.
mXWalkView.load("http://www.w3.org/2010/05/video/mediaevents.html", null);

loadAppFromManifest

mXWalkView.loadAppFromManifest("file:///android_asset/manifest.json", null);

manifest.json

{
  "name": "ManifestTest",
  "start_url": "index.html",
  "description": "Manifest test",
  "version": "1.0.0"
}

声明

欢迎转载，但请保留文章原始出处

作者：GavinCT

出处：      http://www.cnblogs.com/ct2011/