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Android中AsyncTask使用实例

MainActivity如下:

[java]
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一个实例,新建的任务只能执行一次,否则会出现异常 
                //2 异步任务的实例必须在UI线程中创建 
                //3 execute()方法必须在UI线程中调用。 
                downLoaderAsyncTask=new DownLoaderAsyncTask(); 
                downLoaderAsyncTask.execute("http://www.baidu.com"); 
                break; 
            case R.id.cancelButton: 
                //取消一个正在执行的任务,onCancelled()方法将会被调用    
                downLoaderAsyncTask.cancel(true); 
                break; 
            default: 
                break; 
            } 
        } 
        
   } 
   //构造函数AsyncTask<Params, Progress, Result>参数说明:  
   //Params   启动任务执行的输入参数 
   //Progress 后台任务执行的进度 
   //Result   后台计算结果的类型 
   private class DownLoaderAsyncTask extends AsyncTask<String, Integer, String>{ 
    //onPreExecute()方法用于在执行异步任务前,主线程做一些准备工作    
    @Override 
    protected void onPreExecute() { 
        super.onPreExecute(); 
        textView.setText("调用onPreExecute()方法--->准备开始执行异步任务"); 
        System.out.println("调用onPreExecute()方法--->准备开始执行异步任务"); 
    } 
     
    //doInBackground()方法用于在执行异步任务,不可以更改主线程中UI  
    @Override 
    protected String doInBackground(String... params) { 
       System.out.println("调用doInBackground()方法--->开始执行异步任务"); 
        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); 
          &

补充:移动开发 , Android ,
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