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PhoneGap 插件简介
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一、PhoneGap平台

前不久PhoneGap发布了1.0版本,这为移动开发大家族提供了又一个跨平台的解决方案。开发者只要有JavaScript、CSS3、Html5的基础就可以快速开发移动应用,并且一次开发支持iOS、iOS(xcode 4)、Android、WebOS、Blackberry、Symbian 六大平台。不过,JavaScript的速度虽然在近些年提高了100倍,其速度还是无法和原生代码相比。在编写复杂的业务逻辑时JavaScript显得力不从心。那么PhoneGap有没有办法解决这个问题呢?答案是肯定的。PhoneGap平台提供了插件功能,开发者可以将重量级的功能封装在原生代码开发的插件中,并将接口暴露给JavaScript,JavaScript在调用插件功能时都是非阻塞的,所以并不影响JavaScript层的性能。下面我们就看看如何编写和调用一个PhoneGap插件吧。

二、编写插件

由于要写原生代码,所以各个平台插件的编写略有不同。我们以Android为例吧。这个是PhoneGap官方的例子,原文网址: http://wiki.phonegap.com/w/page/36753494/How%20to%20Create%20a%20PhoneGap%20Plugin%20for%20Android 需要翻*墙。

1.插件功能

PhoneGap提供了文件读写的Api,但没有提供列出文件清单的功能。我们编写一个名为 DirectoryListingPlugin 的插件来实现列表SDCARD上文件的功能吧。

2.创建一个Android工程

如下图所示:
step1



3.包含PhoneGap依赖

  • 下载PhoneGap并解压
  • 在工程根目录新建目录/libs
  • 拷贝 phonegap.jar 到 /libs
注:由于是写插件,所以只有phonegap.jar就够了。要建立完整的PhoneGap应用,可参考http://www.phonegap.com/start/#android 

4.实现插件类




代码:
/**
 * Example of Android PhoneGap Plugin
 */
package com.trial.phonegap.plugin.directorylisting;


import java.io.File;


import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;


import android.util.Log;


import com.phonegap.api.Plugin;
import com.phonegap.api.PluginResult;
import com.phonegap.api.PluginResult.Status;


/**
 * PhoneGap plugin which can be involved in following manner from javascript
 * <p>
 * result example -
 * {"filename":"/sdcard","isdir":true,"children":[{"filename":"a.txt"
 * ,"isdir":false},{..}]}
 * </p>
 * 
 * <pre>
 * {@code
 * successCallback = function(result){
 *     //result is a json
 *  
 * }
 * failureCallback = function(error){
 *     //error is error message
 * }
 * 
 * DirectoryListing.list("/sdcard",
 * 		  successCallback
 * 		  failureCallback);
 * 	                               
 * }
 * </pre>
 * 
 * @author Rohit Ghatol
 * 
 */
public class DirectoryListPlugin extends Plugin {
	/** List Action */
	public static final String ACTION = "list";


	/*
	 * (non-Javadoc)
	 * 
	 * @see com.phonegap.api.Plugin#execute(java.lang.String,
	 * org.json.JSONArray, java.lang.String)
	 */
	@Override
	public PluginResult execute(String action, JSONArray data, String callbackId) {
		Log.d("DirectoryListPlugin", "Plugin Called");
		PluginResult result = null;
		if (ACTION.equals(action)) {
			try {
				String fileName = data.getString(0);
				JSONObject fileInfo = getDirectoryListing(new File(fileName));
				Log
						.d("DirectoryListPlugin", "Returning "
								+ fileInfo.toString());
				result = new PluginResult(Status.OK, fileInfo);
			} catch (JSONException jsonEx) {
				Log.d("DirectoryListPlugin", "Got JSON Exception "
						+ jsonEx.getMessage());
				result = new PluginResult(Status.JSON_EXCEPTION);
			}
		} else {
			result = new PluginResult(Status.INVALID_ACTION);
			Log.d("DirectoryListPlugin", "Invalid action : " + action
					+ " passed");
		}
		return result;
	}


	/**
	 * Gets the Directory listing for file, in JSON format
	 * 
	 * @param file
	 *            The file for which we want to do directory listing
	 * @return JSONObject representation of directory list. e.g
	 *         {"filename":"/sdcard"
	 *         ,"isdir":true,"children":[{"filename":"a.txt"
	 *         ,"isdir":false},{..}]}
	 * @throws JSONException
	 */
	private JSONObject getDirectoryListing(File file) throws JSONException {
		JSONObject fileInfo = new JSONObject();
		fileInfo.put("filename", file.getName());
		fileInfo.put("isdir", file.isDirectory());
		if (file.isDirectory()) {
			JSONArray children = new JSONArray();
			fileInfo.put("children", children);
			if (null != file.listFiles()) {
				for (File child : file.listFiles()) {
					children.put(getDirectoryListing(child));
				}
			}
		}
		return fileInfo;
	}
}
5.将插件类导出成jar 包

Eclipse中如下操作:

  • 在要生成jar的项目上右击,选择菜单上的Export(导出)
  • 导出类型选择Jar File
  • 选择或者输入生成路径
  • 选择要导出的类
我们导出成directorylist.jar

6.实现JavaScript插件

  • 创建一个名为DirectoryListing的类
  • 创建一个成员函数list()
  • 在成员函数中调用PhoneGap.exec(<<successCallback>>,<<failureCallback>>,<<Plugin Name>>,<<Action Name>>,<<Arguments Array>>);
  • 将js文件保存为directorylisting.js

代码:

/**
 *  
 * @return Object literal singleton instance of DirectoryListing
 */
var DirectoryListing = { 
/**
 * @param directory The directory for which we want the listing
 * @param successCallback The callback which will be called when directory listing is successful
 * @param failureCallback The callback which will be called when directory listing encouters an error
 */
    list: function(directory,successCallback, failureCallback) {
        return PhoneGap.exec(successCallback,        //Success callback from the plugin
	     failureCallback,        //Error callback from the plugin
	     'DirectoryListPlugin',  //Tell PhoneGap to run "DirectoryListingPlugin" Plugin
	     'list',                 //Tell plugin, which action we want to perform
	     [directory]);           //Passing list of args to the plugin
    }
};

三、测试

1.创建一个PhoneGap应用 http://www.phonegap.com/start/#android

2.将 directorylisting.jar 加入工程依赖

3.将directorylisting.js放入到 /assets/www 目录下。

4.在 /res/xml/plugins.xml 文件中添加 

<plugin name="DirectoryListPlugin" 
	value="com.trial.phonegap.plugin.directorylisting.DirectoryListPlugin" />

5.在index.html中调用DirectoryListing.list

代码:

<!DOCTYPE HTML>
<html>
     <head>
          <title>PhoneGap</title>
     </head>
     <body>
          <!-- Button -->
          <input disabled id="list-sdcard" type="button" value="List SDCard Contents"  />
          <hr>
 
          <!-- Place Holder for placing the SD Card Listing -->
          <div id="result"></div>
 
          <hr>
 
          <script type="text/javascript" src="phonegap-1.0.0.js"></script>
          <script type="text/javascript" src="directorylisting.js"></script>
          <script type="text/javascript" >
   document.addEventListener('deviceready', function() {
   var btn = document.getElementById("list-sdcard");
   btn.onclick = function() {
    DirectoryListing.list(    "/sdcard",
function(r){printResult(r)},
function(e){log(e)}
);
    }
    btn.disabled=false;
  }, true);
 
 
 function printResult(fileInfo){
  var innerHtmlText=getHtml(fileInfo);    
  document.getElementById("result").innerHTML=innerHtmlText;
 }
 
 function getHtml(fileInfo){
 var htmlText="<ul><li>"+fileInfo.filename;
 if(fileInfo.children){
 
 for(var index=0;index<fileInfo.children.length;index++){
 htmlText=htmlText+getHtml(fileInfo.children[index]);
 }
 }
 htmlText=htmlText+"</li></ul>";
 return htmlText;
 
 } 
          </script>
 
     </body>
</html>

至此,一个PhoneGap Android插件就成完了。

文章转自 : http://blog.csdn.net/yyan/article/details/6664863

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