android的AsyncTask用法实践

写了个demo实践异步任务AsyncTask的用法，异步下载网络图片并显示以及模拟进度条、取消异步任务等，大致分以下几部分：

package com.alipay.asynctasktest;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity {

    private Button button;
    private Button progressBtn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = (Button) findViewById(R.id.button);
        progressBtn = (Button) findViewById(R.id.progressBtn);
        button.setOnClickListener(new ButtonClickListener());
        progressBtn.setOnClickListener(new ProgressButtionClickListener());
    }

    class ButtonClickListener implements OnClickListener {

        @Override
        public void onClick(View v) {
            startActivity(new Intent(MainActivity.this, ImageActivity.class));
        }

    }

    class ProgressButtionClickListener implements OnClickListener {

        @Override
        public void onClick(View v) {
            startActivity(new Intent(MainActivity.this, ProgressActivity.class));
        }

    }
}

/**
 * Alipay.com Inc.
 * Copyright (c) 2004-2015 All Rights Reserved.
 */
package com.alipay.asynctasktest;

import java.io.BufferedInputStream;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ImageView;
import android.widget.ProgressBar;

//AsyncTask注意事项
//必须在UI线程中创建AsyncTask的实例
//必须在UI线程中调用AsyncTask的execute()方法
//重写的四个方法是系统自动调用的，不应手动调用
//每个AsyncTask只能被执行一次，多次调用将会引发异常

/**
 * 
 * @author quyang.ybb
 * @version $Id: ImageActivity.java, v 0.1 2015年10月3日 下午4:12:02 quyang.ybb Exp $
 */
public class ImageActivity extends Activity {

    private ImageView     mImageView;
    private ProgressBar   mProgressBar;
    private static String URL = "https://img-my.youkuaiyun.com/uploads/201504/12/1428806103_9476.png";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.image);
        mImageView = (ImageView) findViewById(R.id.image);
        mProgressBar = (ProgressBar) findViewById(R.id.pb);
        MyAsyncTask task = new MyAsyncTask();
        task.execute(URL);
    }

    /**
     * 异步下载图片
     * @author quyang.ybb
     * @version $Id: MyAsyncTask.java, v 0.1 2015年10月3日 下午12:04:43 quyang.ybb Exp $
     */
    public class MyAsyncTask extends AsyncTask<String, Integer, Bitmap> {

        // 线程开始前的工作
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            Log.d("aysnctask", "onPreExecute");
            mProgressBar.setVisibility(View.VISIBLE);
        }

        @Override
        protected Bitmap doInBackground(String... params) {
            Log.d("aysnctask", "doInBackground");
            // 获取传递进来的参数
            String url = params[0];
            Bitmap bitmap = null;
            // 定义网络连接对象
            URLConnection connection;
            // 定义用于获取数据的输入流
            InputStream is;
            // 导入URL包，通过openConnection()获取网络连接对象
            try {
                connection = new URL(url).openConnection();
                // 获取输入流
                is = connection.getInputStream();
                //水管------------------流
                //水流------------------数据流
                //水池-------------------文件
                //水桶-------------------程序
                BufferedInputStream bis = new BufferedInputStream(is);
                //将输入流解析成Bitmap
                Thread.sleep(3000);
                bitmap = BitmapFactory.decodeStream(bis);
                is.close();
                bis.close();
            } catch (Exception e) {
                Log.e("net conn error", "exception");
            }
            return bitmap;
        }

        // 当doInBackground方法调用完之后，就会给onPostExecute方法返回一个Bitmap类型的参数
        // 操作UI，设置图像
        @Override
        protected void onPostExecute(Bitmap bitmap) {
            Log.d("aysnctask", "onPostExecute");
            mProgressBar.setVisibility(View.INVISIBLE);
            mImageView.setImageBitmap(bitmap);
        }

        @Override
        protected void onProgressUpdate(Integer... values) {
            super.onProgressUpdate(values);
        }

    }

}

/**
 * Alipay.com Inc.
 * Copyright (c) 2004-2015 All Rights Reserved.
 */
package com.alipay.asynctasktest;

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

/**
 * 
 * @author quyang.ybb
 * @version $Id: ProgressActivity.java, v 0.1 2015年10月7日 下午2:05:10 quyang.ybb Exp $
 */
public class ProgressActivity extends Activity {

    private ProgressBar mProgressBar;
    private MyAsyncTask mTask;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.progressbar);
        mProgressBar = (ProgressBar) findViewById(R.id.progressBar);
        mTask = new MyAsyncTask();
        mTask.execute();
    }

    @Override
    protected void onPause() {
        super.onPause();
        if (mTask != null && mTask.getStatus() == AsyncTask.Status.RUNNING) {
            mTask.cancel(true);
        }
    }

    // 为了能取消异步任务，需要将其与Activity或Fragment的生命周期绑定在一起
    public class MyAsyncTask extends AsyncTask<Void, Integer, Void> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            Log.d("ProgressActivity", "onPreExecute");
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            Log.d("ProgressActivity", "onPostExecute");
        }

        //运行在其他线程，其余运行在主流程（可以做更新UI的操作）
        @Override
        protected Void doInBackground(Void... params) {
            // 模拟进度更新
            for (int i = 0; i < 100; i++) {
                if (isCancelled()) {
                    break;
                }
                publishProgress(i);
                try {
                    Thread.sleep(300);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
            return null;
        }

        @Override
        protected void onProgressUpdate(Integer... values) {
            super.onProgressUpdate(values);
            mProgressBar.setProgress(values[0]);
        }
    }
}

<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"
    tools:context="${relativePackage}.${activityClass}" >

    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/loadImage" />

    <Button 
        android:id="@+id/progressBtn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/loadProgress"/>
    
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="30dp" >

    <ImageView
        android:id="@+id/image"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <ProgressBar
        android:id="@+id/pb"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:visibility="gone" />

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <ProgressBar
        android:id="@+id/progressBar"
        style="?android:attr/progressBarStyleHorizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true" />

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="app_name">com.alipay.asynctasktest</string>
    <string name="hello_world">Hello world!</string>
    <string name="loadImage">Load Image</string>
    <string name="loadProgress">Load ProgressBar</string>
</resources>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.alipay.asynctasktest"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-permission android:name="android.permission.INTERNET" />

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="21" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".ImageActivity" >
        </activity>
        <activity android:name=".ProgressActivity" >
        </activity>
    </application>

</manifest>