昨天和女朋友換了手機，我的iPhone 4S 換了她得三星I9003。第一感覺就是好卡，果斷刷機。以前是Android 2.3的系統。回來刷成了4.4。

好了，問題來了。在我用手機測試我們的APP的時候，丟擲一個如題的異常：android.os.NetworkOnMainThreadException

第一次看到這異常，字面意思是說：在主執行緒中的網路異常。然後我就去了解了下這個異常，先看看官方的說明： 

NetworkOnMainThreadException

Class Overview

The exception that is thrown when an application attempts to perform a networking operation on its main thread.

This is only thrown for applications targeting the Honeycomb SDK or higher. Applications targeting earlier SDK versions are allowed to do networking on their main event loop threads, but it's heavily discouraged. See the document Designing for Responsiveness.

Also see StrictMode.

所以事情就很清楚了。一個APP如果在主執行緒中請求網路操作，將會丟擲此異常。Android這個設計是為了防止網路請求時間過長而導致介面假死的情況發生。

解決方案有兩個，一個是使用StrictMode，二是使用執行緒來操作網路請求。

if (android.os.Build.VERSION.SDK_INT > 9) {  
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();  
    StrictMode.setThreadPolicy(policy);  
}  

public void onCreate(Bundle savedInstanceState) {  
    super.onCreate(savedInstanceState);  
    this.setContentView(R.layout.main_view);  
    new Thread(runnable).start();  
}  
   
Handler handler = new Handler(){  
    @Override  
    public void handleMessage(Message msg) {  
        super.handleMessage(msg);  
        Bundle data = msg.getData();  
        String val = data.getString("value");  
        Log.i(TAG,"請求結果:" + val);  
    }  
}  
   
Runnable runnable = new Runnable(){  
    @Override  
    public void run() {  
        // TODO: http request.  
        Message msg = new Message();  
        Bundle data = new Bundle();  
        data.putString("value","請求結果");  
        msg.setData(data);  
        handler.sendMessage(msg);  
    }  
}  

上面是比較通用的方法，我的程式碼：

// Android 4.0 之後不能在主執行緒中請求HTTP請求  
            new Thread(new Runnable(){  
                @Override  
                public void run() {  
                    cachedImage = asyncImageLoader.loadDrawable(imageUrl, position);  
                    imageView.setImageDrawable(cachedImage);  
                }  
            }).start();