AsyncTask异步任务使用详细实例(二)

MainActivity如下:

package cn.cc;import java.io.InputStream;import java.net.HttpURLConnection;import java.net.URL;import cn.cc.AsyncTaskSubClass.AsyncTaskCallbackInterface;import cn.cc.AsyncTaskSubClass.AsyncTaskPerformInterface;import android.app.Activity;import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.Bundle;import android.widget.ImageView;/** * Demo描述: * 平常我们写一个AsyncTask的时候把异步操作已经异步完成后的操作 * 是放在doInBackground()和onPostExecute()方法中的. * 这样显得代码比较臃肿,而且不方便复用. * 所以在此采用AsyncTask与回调结合的方式:抽象AsyncTask的代码从而 * 简化代码,并且利于重用. */public class MainActivity extends Activity {private Context mContext;private ImageView mImageView;private AsyncTaskSubClass mAsyncTaskSubClass;private String mFavIconPathString =null;private final String FAVICON_SERVICE="http://www.google.com/s2/favicons?domain=";    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        init();    }        private void init(){    mContext=this;    mImageView=(ImageView) findViewById(R.id.imageView);    mFavIconPathString = FAVICON_SERVICE+"http://www.ifeng.com/";        startAsyncTask();    }    private void startAsyncTask() {mAsyncTaskSubClass = new AsyncTaskSubClass(mContext,new AsyncTaskPerformInterface() {@Overridepublic Bitmap performAsyncTask(String string) {try {Bitmap bitmap=null;InputStream inputStream = null;URL imageUrl = new URL(string);HttpURLConnection httpURLConnection = (HttpURLConnection) imageUrl.openConnection();httpURLConnection.setConnectTimeout(5000);httpURLConnection.setRequestMethod("GET");if (httpURLConnection.getResponseCode() == 200) {inputStream = httpURLConnection.getInputStream();bitmap = BitmapFactory.decodeStream(inputStream);return bitmap;}} catch (Exception e) {}return null;}}, new AsyncTaskCallbackInterface() {@Overridepublic void asyncTaskFinishCallback(Bitmap bitmap) {mImageView.setImageBitmap(bitmap);}});//开始执行一个异步任务mAsyncTaskSubClass.execute(mFavIconPathString);}}

AsyncTaskSubClass如下:

package cn.cc;import android.content.Context;import android.graphics.Bitmap;import android.os.AsyncTask;//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public class AsyncTaskSubClass extends AsyncTask<String, Integer, Bitmap> {private Context mContext;private AsyncTaskPerformInterface mAsyncTaskPerformInterface;private AsyncTaskCallbackInterface mAsyncTaskCallbackInterface;public AsyncTaskSubClass(     Context context,     AsyncTaskPerformInterface asyncTaskPerformInterface,     AsyncTaskCallbackInterface asyncTaskCallbackInterface) {super();this.mContext = context;this.mAsyncTaskPerformInterface = asyncTaskPerformInterface;this.mAsyncTaskCallbackInterface = asyncTaskCallbackInterface;}//执行异步操作的回调接口public interface AsyncTaskPerformInterface {public Bitmap performAsyncTask(String string);}//异步操作完成的回调接口public interface AsyncTaskCallbackInterface {public void asyncTaskFinishCallback(Bitmap bitmap);}@Overrideprotected void onPreExecute() {super.onPreExecute();System.out.println("调用onPreExecute()方法--->准备开始执行异步任务");  }//此处strings[0]对应于AsyncTask<String, Integer, Bitmap>//中的第一个参数,即异步任务的输入参数.//此处Bitmap对应于AsyncTask<String, Integer, Bitmap>//中的第三个参数,即异步任务的输出结果.@Overrideprotected Bitmap doInBackground(String... strings) {System.out.println("调用doInBackground()方法--->开始执行异步任务");Bitmap bitmap=null;if(mAsyncTaskPerformInterface!=null){bitmap=mAsyncTaskPerformInterface.performAsyncTask(strings[0]);}return bitmap;}//此处Bitmap对应于AsyncTask<String, Integer, Bitmap>//中的第三个参数,即异步任务的输出结果.@Overrideprotected void onPostExecute(Bitmap bitmap) {System.out.println("调用onPostExecute()方法--->异步任务执行完毕");if(mAsyncTaskCallbackInterface!=null){mAsyncTaskCallbackInterface.asyncTaskFinishCallback(bitmap);}}//异步执行时在主线程中更新异步任务的执行信息//此处values[0]对应于AsyncTask<String, Integer, Bitmap>//中的第二个参数,即异步任务的执行进度.@Overrideprotected void onProgressUpdate(Integer... values) {return;}//异步任务被取消时,在主线程中执行相关的操作 @Overrideprotected void onCancelled() {super.onCancelled();System.out.println("调用onCancelled()方法--->异步任务被取消");}}

main.xml如下:

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:background="#ffffff">    <ImageView        android:id="@+id/imageView"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_centerInParent="true" /></RelativeLayout>