自己动手写AsyncTask

悠悠 2022-09-24 01:20 238阅读 0赞

本文依赖上一篇文章：[自己动手写消息机制][Link 1]

在javaSE中模拟Android的AsyncTask异步任务

package com.zhanjixun;
    
    public abstract class AsyncTask<Params, Progress, Result> {
    	private static final int onProgress = 1;
    	private static final int onPost = 2;
    
    	private boolean exeuted = false;// 实现一个任务只能执行一次
    
    	private Handler mHandler = new Handler() {
    
    		@SuppressWarnings("unchecked")
    		public void handlerMessage(Message message) {
    			if (message.what == onProgress) {
    				onProgressUpdate((Progress[]) message.obj);
    			}
    			if (message.what == onPost) {
    				onPostExecute((Result) message.obj);
    			}
    		}
    	};
    
    	/**
    	 * 在执行后台任务之前，在主线程调用
    	 */
    	protected void onPreExecute() {
    	}
    
    	/**
    	 * 执行后台任务的代码都放在这里
    	 * 
    	 * @param params
    	 */
    	protected abstract Result doInBackground(Params... params);
    
    	protected void onProgressUpdate(Progress... progress) {
    
    	}
    
    	/**
    	 * 在执行后台任务之后，在主线程调用
    	 */
    	protected void onPostExecute(Result params) {
    	}
    
    	/**
    	 * 发送一个消息到主线程中，这是过程是异步的，就是说后台任务发送了消息给主线程之后马上继续往下运行
    	 * 
    	 * @param progress
    	 */
    	protected final void publishProgress(Progress... progress) {
    		Message msg = new Message();
    		msg.what = onProgress;
    		msg.obj = progress;
    		mHandler.sendMessage(msg);
    	}
    
    	public final void execute(Params... params) {
    		if (exeuted) {
    			throw new RuntimeException("不能运行两次");
    		}
    		onPreExecute();
    		// 简单来就好了，直接启动新的线程，而Android中的AsyncTask的各个子类的任务是同步的，这里是异步的
    		new Thread(new Runnable() {
    
    			@Override
    			public void run() {
    				Result result = doInBackground(params);
    				exeuted = true;// 执行完了
    
    				Message msg = new Message();
    				msg.what = onPost;
    				msg.obj = result;
    				mHandler.sendMessage(msg);
    			}
    		}).start();
    	}
    }

测试类：

package com.zhanjixun.test;
    
    import java.util.Random;
    
    import com.zhanjixun.AsyncTask;
    import com.zhanjixun.Looper;
    
    public class AsyncTaskDemo {
    
    	public static void main(String[] args) {
    		Looper.prepare();// 将主线程变成轮询线程
    		new MyAsyncTask().execute();
    		Looper.loop();
    	}
    
    	/**
    	 * 模拟下载文件
    	 * 
    	 * @author doudian
    	 *
    	 */
    	public static class MyAsyncTask extends AsyncTask<String, Integer, Boolean> {
    
    		@Override
    		protected Boolean doInBackground(String... params) {
    			int count = 0;
    			Random random = new Random();
    			while (count <= 100) {
    				String format = String.format("后台中下载文件(%d/100)...（%s线程打印）",
    						count, Thread.currentThread().getName());
    				System.err.println(format);
    				publishProgress(count);
    				// 耗时下载
    				try {
    					Thread.sleep(200);
    				} catch (InterruptedException e) {
    					e.printStackTrace();
    				}
    
    				int nextInt = random.nextInt(20);
    				count += nextInt;
    			}
    			return true;
    		}
    
    		@Override
    		protected void onProgressUpdate(Integer... progress) {
    			String format = String.format("【提示用户】正在下载文件(%d/100)...（%s线程打印）",
    					progress[0], Thread.currentThread().getName());
    			System.out.println(format);
    		}
    
    		@Override
    		protected void onPostExecute(Boolean params) {
    			String object = params ? "成功" : "失败";
    			String format = String.format("任务结束，下载文件%s（%s线程打印）", object, Thread
    					.currentThread().getName());
    			System.out.println(format);
    		}
    	}
    }

测试结果具有随机性：

![Center][]

源代码：[http://download.csdn.net/detail/zhanjixun/9583224][http_download.csdn.net_detail_zhanjixun_9583224]

[Link 1]: http://blog.csdn.net/zhanjixun/article/details/51981055
[Center]: /images/20220720/b80f978976784e9987540cbbce8caceb.png
[http_download.csdn.net_detail_zhanjixun_9583224]: http://download.csdn.net/detail/zhanjixun/9583224