android笔记--AsyncTask例子

代码：

package com.test.handler;
 
import com.test.demo.R;
 
import android.app.Activity;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
 
public class AsyncTaskTestActivity extends Activity {
 
    private TextView textView;
    private ProgressDialog dialog;
    
    //Counter 用于保存中间结果
    private class Counter {
        public int progress;
        public int sum;
 
        public Counter(int progress, int sum) {
            this.progress = progress;
            this.sum = sum;
        }
 
    }
    
//定义AsyncTask子类，传给任务的参数Void,处理中间结果类型为Counter类型，处理最终结果为Integer类型
    private class MyTask extends AsyncTask<Void, Counter, Integer> {
        @Override
        protected void onPreExecute() {
            // TODO Auto-generated method stub
            super.onPreExecute();
            textView.setText("result:0");
            dialog.show();
        }
 
        @Override
        protected Integer doInBackground(Void... params) {
            int sum = 0;
            try {
                for (int i = 0; i < 100; i++) {
                    sum += i * 2;
                    //发布中间结果，onProgressUpdate函数对中间结果进行处理，可以在UI组件上显示进度
                    publishProgress(new Counter(i, sum));
                    Thread.sleep(40);
                }
            } catch (Exception e) {
                // TODO: handle exception
                e.printStackTrace();
            }
            //返回最终处理结果
            return Integer.valueOf(sum);
        }
 
        @Override
        protected void onProgressUpdate(Counter... values) {
            // 中间结果处理：设置进度条，textView上显示目前累加的结果
            dialog.setProgress(values[0].progress);
            textView.setText("result:" + values[0].sum);
 
        }
        
        // doInBackground处理完成后执行
        @Override
        protected void onPostExecute(Integer result) {
            super.onPostExecute(result);
            dialog.dismiss();
            textView.setText("result:" + result);
        }
    }
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_handler_test2);
        dialog = new ProgressDialog(this);
        dialog.setTitle("start");
        dialog.setIcon(R.drawable.ic_dialog_load);
        dialog.setMessage("please wait");
        dialog.setMax(100);
        dialog.setProgress(0);
        dialog.setIndeterminate(false);
        dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
        dialog.setCancelable(false);
 
        textView = (TextView) findViewById(R.id.result2);
 
    }
 
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.handler_test2, menu);
        return true;
    }
 
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        } else if (id == R.id.action_reflash2) {
        	//启动任务，每次都是创建新的任务对象
            new MyTask().execute();
            return true;
        }
 
        return super.onOptionsItemSelected(item);
    }
 
}

 layout文件：

<RelativeLayout 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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.test.handler.AsyncTaskTestActivity" >

    <TextView
        android:id="@+id/result2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

</RelativeLayout>

Android doc上给出的规定：

Threading rules

---

There are a few threading rules that must be followed for this class to work properly:

• The AsyncTask class must be loaded on the UI thread. This is done automatically as of JELLY_BEAN.
• The task instance must be created on the UI thread.
• execute(Params...) must be invoked on the UI thread.
• Do not call onPreExecute(), onPostExecute(Result), doInBackground(Params...), onProgressUpdate(Progress...) manually.
• The task can be executed only once (an exception will be thrown if a second execution is attempted.)