android 异步任务AsyncTask

package com.example.asynctestdemo;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;

public class MainActivity extends Activity {
	private Button bt_execute;
	private Button bt_cancel;
	private ProgressBar progressBar;
	private TextView textView;
	MyTask myTask;

	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		bt_execute = (Button) findViewById(R.id.bt_execute);
		bt_cancel = (Button) findViewById(R.id.bt_cancel);
		progressBar = (ProgressBar) findViewById(R.id.progressBar);
		textView = (TextView) findViewById(R.id.text_view);

		bt_execute.setOnClickListener(new OnClickListener() {

			public void onClick(View v) {
				// 实例化异步任务MyTask类
				myTask = new MyTask();
				myTask.execute("http://www.baidu.com");
			}
		});

		bt_cancel.setOnClickListener(new OnClickListener() {

			public void onClick(View v) {
				myTask.cancel(true);
			}
		});

	}

	class MyTask extends AsyncTask<String, Integer, String> {

		// onpreExecute()方法用于，在执行后台任务前，做一些UI操作
		protected void onPreExecute() {
			textView.setText("Loading......");
		}

		// doInBackground()方法，内部执行后台耗时任务操作，但不是不能在此方法内修改UI
		protected String doInBackground(String... params) {
			try {
				HttpClient client = new DefaultHttpClient();
				HttpGet get = new HttpGet(params[0]);
				HttpResponse response = client.execute(get);
				if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
					HttpEntity entity = response.getEntity();
					InputStream is = entity.getContent();
					long total = entity.getContentLength();
					System.out.println(total);
					ByteArrayOutputStream baos = new ByteArrayOutputStream();
					byte[] buf = new byte[1024];
					int count = 0;
					int length = -1;
					while ((length = is.read(buf)) != -1) {
						baos.write(buf, 0, length);
						count+=length;
						// 调用publishProgress()方法公布进度，最后onProgressUpdata方法将被执行
						publishProgress((int) (count/length));
						//为了更明显的展现效果,每次暂停0.5s
						Thread.sleep(500);
					}
					return new String(baos.toByteArray(), "utf-8");
				}
			} catch (ClientProtocolException e) {
				e.printStackTrace();
			} catch (IOException e) {
				e.printStackTrace();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			return null;
		}

		// onProgressUpdata方法，用于更新进度信息，例如执行进度条程序
		protected void onProgressUpdate(Integer... values) {
			progressBar.setProgress(values[0]);
			textView.setText("Loading......" + values[0]);
		}

		// onPostExecute方法，用于在执行完后台任务后，更新ＵＩ，显示结果
		protected void onPostExecute(String result) {
			textView.setText(result);
		}

		// onCacelled方法，用于在取消执行中的任务时，更改ＵＩ
		protected void onCancelled() {
			textView.setText("cancelled");
			progressBar.setProgress(0);
		}

	}
}