从网络上获取图片的两种方式讲解：thread+handle和AsyncTask方式

    从网络上获取图片是一个比较耗时的操作，放在主线程会导致阻塞主线程，响应超时，所以我们不能把它放在主线程里操作，必须放在一个子线程里，我打算采用两种方式去实现。1、采用thread去获取图片，获取到后通过handle把消息发送到与主线程绑定的消息队列中（也就是主线程的loop）。2、采用AsyncTask方式，也称异步任务，这个类其实把子线程和handle的处理方式进行了封装，建议开发者多用异步任务来处理，但是对thread和handle的原理一定要搞清楚。

 

效果图如下：

 



下面先采用第一种方式：

public class MainActivity extends Activity {

private Button button;
private ImageView imageView;
private ProgressBar progressBar;
private MyHandle handle;
private final static int CODE =1;
private final static String URL = "http://pic10.nipic.com/20101016/5311590_152428004670_2.jpg";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = (Button)findViewById(R.id.button);
imageView = (ImageView)findViewById(R.id.imageview);
progressBar = (ProgressBar)findViewById(R.id.progress);
handle = new MyHandle();
button.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
progressBar.setVisibility(View.VISIBLE);
new DownThread(URL).start();
}
});
}

public class DownThread extends Thread{
String url2;
public DownThread(String url){
this.url2 = url;
}
@Override
public void run() {
InputStream inputStream = null;
HttpURLConnection connection = null;
try {
URL url = new URL(url2);
//OutputStream outputStream = null;
connection = (HttpURLConnection) url.openConnection();
if(connection.getResponseCode() == 200){
inputStream = connection.getInputStream();
}
Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
Message msg = Message.obtain();
msg.obj = bitmap;
msg.arg1 = CODE;
handle.sendMessage(msg);
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
if(inputStream!=null){
try {
inputStream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(connection!=null){
connection.disconnect();
}
}
}
}

private class MyHandle extends Handler{
public MyHandle(){

}
@Override
public void handleMessage(Message msg) {
// TODO Auto-generated method stub
switch (msg.arg1) {
case CODE:
Bitmap bitmap = (Bitmap)msg.obj;
imageView.setVisibility(View.VISIBLE);
progressBar.setVisibility(View.GONE);
imageView.setImageBitmap(bitmap);
break;
}
}
}

AsyncTask方式：

public class MainActivity extends Activity {

private Button button;
private ProgressBar progressBar;
private ImageView imageView;
private final static String URL = "http://pic10.nipic.com/20101016/5311590_152428004670_2.jpg";

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = (Button) findViewById(R.id.button);
imageView = (ImageView) findViewById(R.id.imageview);
progressBar = (ProgressBar) findViewById(R.id.progress);
button.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
new DownloadTast().execute(URL);
}
});
}

private class DownloadTast extends AsyncTask<String, Void, Bitmap> {

@Override
protected void onPreExecute() {
progressBar.setVisibility(View.VISIBLE);
}

@Override
protected Bitmap doInBackground(String... params) {
// TODO Auto-generated method stub
String urls = params[0];
InputStream inputStream = null;
Bitmap bitmap = null;
HttpURLConnection connection =null;
try {
URL url = new URL(urls);
connection = (HttpURLConnection) url
.openConnection();
if (connection.getResponseCode() == 200) {
inputStream = connection.getInputStream();
bitmap = BitmapFactory.decodeStream(inputStream);
}
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
if(inputStream!=null){
try {
inputStream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(connection !=null){
connection.disconnect();
}
}
return bitmap;

}

@Override
protected void onPostExecute(Bitmap result) {
imageView.setVisibility(View.VISIBLE);
imageView.setImageBitmap(result);
progressBar.setVisibility(View.GONE);
}
}

源码下载