Andriod文件下載含服務器端（客戶端 UI界面異步請求部分）三

本文采用AsyncTask來實現異步請求，具體代碼如下：

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);
	  
	  //獲取傳過來的用戶名
	  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("請耐心等待，文件正在下載中....");
	  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 {

	@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);
	}
   }

}

AsyncTask

1. Params, the type of the parameters sent to the task upon execution. 本文傳遞URL數據
2. Progress, the type of the progress units published during the background computation.//進度條
3. Result, the type of the result of the background computation. //結果 本文未采用進度條形式，只使用了ProgressDialog，故第二個參數置為空，第三個參數選取時，本文在httpUtils包類已經寫入文件到sd卡，故也置為空。

    

   重寫的方法：

    

   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主線程中，初始化參數
   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. 非主線程，耗時操作
   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. 結果更新