Andriod文件下载含服务器端（客户端 UI界面异步请求部分）三

本文采用AsyncTask来实现异步请求，具体代码如下：

public class downloadActivity extends Activity {

	private TextView myTextView=null;
	private Button button=null;
	private static final String path="http://192.168.0.179:8080/Myweb/download.do";
	private ProgressDialog progressDialog=null;
	private URL url=null;
   @Override
   protected void onCreate(Bundle savedInstanceState) {

	  super.onCreate(savedInstanceState);
	  setContentView(R.layout.download);

	  //获取传过来的用户名
	  Intent intent = getIntent();
	  String value = intent.getStringExtra("username");
	  value="hello"+" "+value;
	   //
	  myTextView = (TextView) findViewById(R.id.textView1);
	  myTextView.setText(value);
	  button=(Button)this.findViewById(R.id.download_btn);
	  progressDialog=new ProgressDialog(this);
	  progressDialog.setCancelable(false);
	  progressDialog.setTitle("提示");
	  progressDialog.setMessage("请耐心等待，文件正在下载中....");
	  try {
		url=new URL(path);
	  } catch (MalformedURLException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	  }
	  button.setOnClickListener(new OnClickListener() {

		public void onClick(View arg0) {
			//progressDialog.show();
			 new DownloadFilesTask().execute(url);

		}
	});

    }

   private class DownloadFilesTask extends AsyncTask<URL, Void, Void> {

	@Override
	protected void onPreExecute() {
		progressDialog.show();
		super.onPreExecute();
	}
	@Override
	protected Void doInBackground(URL... urls) {
		httpUtils.sendDownloadPost(urls[0]);
		return null;
	} 

	@Override
	protected void onPostExecute(Void result) {
		progressDialog.dismiss();
		super.onPostExecute(result);
	}
   }

}

在注册时，使用Intent传递了username数据。

AsyncTask<URL, Void, Void>

主要有三个参数

1. Params, the type of the parameters sent to the task upon execution.  本文传递URL数据
2. Progress, the type of the progress units published during the background computation.//进度条
3. Result, the type of the result of the background computation.  //结果

本文未采用进度条形式，只使用了ProgressDialog，故第二个参数置为空，第三个参数选取时，本文在httpUtils包类已经写入文件到sd卡，故也置为空。

重写的方法：

1. onPreExecute(),
   invoked on the UI thread immediately after the task is executed. This step is normally used to setup the task, for instance by showing a progress bar in the user interface.  UI主线程中，初始化参数
2. doInBackground(Params...),
   invoked on the background thread immediately after onPreExecute() finishes
   executing. This step is used to perform background computation that can take a long time. The parameters of the asynchronous task are passed to this step. The result of the computation must be returned by this step and will be passed back to the last step.
   This step can also use publishProgress(Progress...) to
   publish one or more units of progress. These values are published on the UI thread, in theonProgressUpdate(Progress...) step.
    非主线程，耗时操作
3. onProgressUpdate(Progress...),
   invoked on the UI thread after a call to publishProgress(Progress...).
   The timing of the execution is undefined. This method is used to display any form of progress in the user interface while the background computation is still executing. For instance, it can be used to animate a progress bar or show logs in a text field.
4. onPostExecute(Result),
   invoked on the UI thread after the background computation finishes. The result of the background computation is passed to this step as a parameter.  结果更新