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() {
@Override
public 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() {
@Override
public 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 {
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);
}
@Override
protected 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
//中的第一个参数,即异步任务的输入参数.
//此处Bitmap对应于AsyncTask
//中的第三个参数,即异步任务的输出结果.
@Override
protected 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
//中的第三个参数,即异步任务的输出结果.
@Override
protected 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
//中的第二个参数,即异步任务的执行进度.
@Override
protected 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
@Override
protected void onCancelled() {
super.onCancelled();
System.out.println("调用onCancelled()方法--->异步任务被取消");
}
}
main.xml如下:
