Activity生命周期函数、onSaveInstanceState()和onRestoreInstanceState()的介绍

package com.rotation.demo; 

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.SystemClock;
import android.util.Log;
import android.view.View;
import android.widget.ProgressBar;

/**
 * Android实现屏幕旋转异步下载效果
 * @Description: Android实现屏幕旋转异步下载效果

 * @File: RotationAsyncActivity.java

 * @Package com.rotation.demo

 * @Author Hanyonglu

 * @Date 2012-03-28 下午08:14:57

 * @Version V1.0
 */
public class RotationAsyncActivity extends Activity {
    // 进度条
    private ProgressBar progressBar=null;
    // 异步任务类
    private RotationAsyncTask asyncTask=null;
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        progressBar=(ProgressBar)findViewById(R.id.progress);
        // 获取对象
        asyncTask=(RotationAsyncTask)getLastNonConfigurationInstance();
        
        if (asyncTask==null) {
            asyncTask=new RotationAsyncTask(this);
            asyncTask.execute();
        }else {
            asyncTask.attach(this);
            updateProgress(asyncTask.getProgress());
        
            if (asyncTask.getProgress()>=100) {
                markAsDone();
            }
        }
    }
    
    /**
     * 保存对象
     */
    @Override
    public Object onRetainNonConfigurationInstance() {
        asyncTask.detach();
        
        return asyncTask;
    }
      
    private void updateProgress(int progress) {
        progressBar.setProgress(progress);
    }
      
    private void markAsDone() {
        findViewById(R.id.completed).setVisibility(View.VISIBLE);
    }
     
    // 异步任务类
    private static class RotationAsyncTask extends AsyncTask<Void, Void, Void> {
        private RotationAsyncActivity activity=null;
        private int progress=0;
        
        /**
         * 默认的构造器
         */
        public RotationAsyncTask() {
            // TODO Auto-generated constructor stub
        }
        
        /**
         * 带参构造器
         * @param activity
         */
        public RotationAsyncTask(RotationAsyncActivity activity) {
            attach(activity);
        }
        
        @Override
        protected Void doInBackground(Void... unused) {
            for (int i=0;i<20;i++) {
                SystemClock.sleep(500);
                publishProgress();
            }
          
            return null;
        }
        
        @Override
        protected void onProgressUpdate(Void... unused) {
            if (activity==null) {
                Log.w("RotationAsyncActivity", "onProgressUpdate()");
            }else {
                progress += 5;
                activity.updateProgress(progress);
            }
        }
        
        @Override
        protected void onPostExecute(Void unused) {
            if (activity==null) {
                Log.w("RotationAsyncActivity", "onPostExecute()");
            }else {
                activity.markAsDone();
            }
        }
        
        protected void detach() {
            activity = null;
        }
        
        protected void attach(RotationAsyncActivity activity) {
            this.activity = activity;
        }
        
        protected int getProgress() {
            return progress;
        }
    }
}