[大哉問] Activity/Service/BrocastReceiver/Provider均在UI Thread?

Android Process and thread章節  , 有說明
http://developer.android.com/guide/topics/fundamentals/processes-and-threads.html
All components that run in the same process are instantiated in the UI thread
有兩個原則:

1. Do not block the UI thread
2. Do not access the Android UI toolkit from outside the UI thread

第1點透過thread可解決 , 第2點範例如下:

不安全:

public void onClick(View v) {
    new Thread(new Runnable() {
        public void run() {
            Bitmap b = loadImageFromNetwork("http://example.com/image.png");
            mImageView.setImageBitmap(b);
        }
    }).start();
}

安全

public void onClick(View v) {
    new Thread(new Runnable() {
        public void run() {
            final Bitmap bitmap = loadImageFromNetwork("http://example.com/image.png");
            mImageView.post(new Runnable() {
                public void run() {
                    mImageView.setImageBitmap(bitmap);
                }
            });
        }
    }).start();
}

跨thread要存取UI Thread上的View , 可透過下列Function達成

Activity.runOnUiThread(Runnable)
View.post(Runnable)
View.postDelayed(Runnable, long)

若有多個Client端存取的Component , 如Bound Service或是Content Provider , 會需要Thread Safe的做法 , 避免多個操作均使用GUI Thread , 會透過Thread Pool方式 , 避開Main/GUI Thread