package com.example.asynctasktest;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
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;
import android.widget.Toast;
public class MainActivity extends Activity {
private Button satrtButton;
private Button cancelButton;
private ProgressBar progressBar;
private TextView textView;
private DownLoaderAsyncTask downLoaderAsyncTask;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
initView();
}
public void initView() {
satrtButton=(Button) findViewById(R.id.startButton);
cancelButton=(Button) findViewById(R.id.cancelButton);
satrtButton.setOnClickListener(new ButtonOnClickListener());
cancelButton.setOnClickListener(new ButtonOnClickListener());
progressBar=(ProgressBar) findViewById(R.id.progressBar);
textView=(TextView) findViewById(R.id.textView);
}
private class ButtonOnClickListener implements OnClickListener{
public void onClick(View v) {
switch (v.getId()) {
case R.id.startButton:
//注意:
//1 每次需new一個實例,新建的任務(wù)只能執(zhí)行一次,否則會出現(xiàn)異常
//2 異步任務(wù)的實例必須在UI線程中創(chuàng)建
//3 execute()方法必須在UI線程中調(diào)用。
downLoaderAsyncTask=new DownLoaderAsyncTask();
downLoaderAsyncTask.execute("http://www.baidu.com");
break;
case R.id.cancelButton:
//取消一個正在執(zhí)行的任務(wù),onCancelled()方法將會被調(diào)用 
downLoaderAsyncTask.cancel(true);
break;
default:
break;
}
}
}
//構(gòu)造函數(shù)AsyncTask<Params, Progress, Result>參數(shù)說明: 
//Params 啟動任務(wù)執(zhí)行的輸入?yún)?shù)
//Progress 后臺任務(wù)執(zhí)行的進度
//Result 后臺計算結(jié)果的類型
private class DownLoaderAsyncTask extends AsyncTask<String, Integer, String>{
//onPreExecute()方法用于在執(zhí)行異步任務(wù)前,主線程做一些準(zhǔn)備工作 
@Override
protected void onPreExecute() {
super.onPreExecute();
textView.setText("調(diào)用onPreExecute()方法--->準(zhǔn)備開始執(zhí)行異步任務(wù)");
System.out.println("調(diào)用onPreExecute()方法--->準(zhǔn)備開始執(zhí)行異步任務(wù)");
}
//doInBackground()方法用于在執(zhí)行異步任務(wù),不可以更改主線程中UI 
@Override
protected String doInBackground(String... params) {
System.out.println("調(diào)用doInBackground()方法--->開始執(zhí)行異步任務(wù)");
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();
ByteArrayOutputStream bos = new ByteArrayOutputStream();
byte[] buffer = new byte[1024];
int count = 0;
int length = -1;
while ((length = is.read(buffer)) != -1) {
bos.write(buffer, 0, length);
count += length;
//publishProgress()為AsyncTask類中的方法
//常在doInBackground()中調(diào)用此方法
//用于通知主線程,后臺任務(wù)的執(zhí)行情況.
//此時會觸發(fā)AsyncTask中的onProgressUpdate()方法
publishProgress((int) ((count / (float) total) * 100));
//為了演示進度,休眠1000毫秒
Thread.sleep(1000);
}
return new String(bos.toByteArray(), "UTF-8");
}
} catch (Exception e) {
return null;
}
return null;
}
//onPostExecute()方法用于異步任務(wù)執(zhí)行完成后,在主線程中執(zhí)行的操作
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result); 
Toast.makeText(getApplicationContext(), "調(diào)用onPostExecute()方法--->異步任務(wù)執(zhí)行完畢", 0).show();
//textView顯示網(wǎng)絡(luò)請求結(jié)果
textView.setText(result);
System.out.println("調(diào)用onPostExecute()方法--->異步任務(wù)執(zhí)行完畢");
}
//onProgressUpdate()方法用于更新異步執(zhí)行中,在主線程中處理異步任務(wù)的執(zhí)行信息 
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
//更改進度條
progressBar.setProgress(values[0]);
//更改TextView
textView.setText("已經(jīng)加載"+values[0]+"%");
}
//onCancelled()方法用于異步任務(wù)被取消時,在主線程中執(zhí)行相關(guān)的操作 
@Override
protected void onCancelled() {
super.onCancelled();
//更改進度條進度為0
progressBar.setProgress(0);
//更改TextView
textView.setText("調(diào)用onCancelled()方法--->異步任務(wù)被取消");
System.out.println("調(diào)用onCancelled()方法--->異步任務(wù)被取消");
}
}
}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<Button
android:id="@+id/startButton"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="開始異步任務(wù)" />
<Button
android:id="@+id/cancelButton"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="取消異步任務(wù)" />
<ProgressBar
android:id="@+id/progressBar"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:max="100"
android:progress="0" />
<ScrollView
android:id="@+id/scrollView"
android:layout_width="fill_parent"
android:layout_height="wrap_content" >
<TextView
android:id="@+id/textView"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="test test" />
</ScrollView>
</LinearLayout>