模拟一个 从网络中读取一个图片展示到imageView的操作：
注意事项1:
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
执行此方法用来开辟一个URL请求，该请求在Android4.0版本以后需要放到子线程中实现，主线程已不支持httprequest请求(android2.3仍然支持此项)
InputStream inputStream = conn.getInputStream();
Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
// iv.setImageBitmap(bitmap);
第三句则会报错 :android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
注意事项2: 因为在子线程中不可以对view操作，因为view是在主线程创建的，需要在子线程中以消息的形式通知主线程
new Thread()
{
public void run()
{
try {
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; Shuame)");
int responseCode = conn.getResponseCode();
if(responseCode==200)
{
InputStream inputStream = conn.getInputStream();
Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
// iv.setImageBitmap(bitmap);
//采用传送消息的模式 把view操作消息发给主线程
Message msg = new Message();
msg.what=CHANGE_UI;
msg.obj=bitmap;
handler.sendMessage(msg);
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
Toast.makeText(MainActivity.this, "访问网络失败",0).show();
}
}
}.start();主activity中定义handler:
private Handler handler =new Handler(){
public void handleMessage(android.os.Message msg)
{
if(msg.what==CHANGE_UI)
{
iv.setImageBitmap((Bitmap) msg.obj);
}
};
};