Question

hi mate in all tutorial or example the handler used in a looper is created inside the looper example:

 class LooperThread extends Thread {
      public Handler mHandler;

      public void run() {
          Looper.prepare();

          mHandler = new Handler() {
              public void handleMessage(Message msg) {
                  // process incoming messages here
              }
          };

          Looper.loop();
      }
  }

but if a create the handler before the thread, at example

public Handler mHandler=new Handler() {
              public void handleMessage(Message msg) {
                  // process incoming messages here
              }
          };

is possible associate him at the thread in run() method in a looper or i must create him only in run method inside the looper ?

Answer 1

The constructor in Handler basically looks like this:

public Handler() {
    ....
    mLooper = Looper.myLooper();
    if (mLooper == null) {
       // throws an exception
    }
    ....
}

The field, mLooper is a package-private final field – and, of course, there’s no setter available for you to change it later on.

In short, the Handler() constructor will associate itself with Looper.myLooper(), there are other constructors that allow you to pass the Looper – but these would also require you to create the Looper prior to creating your Handler.