who calls Activity.dispatchTouchEvent( event )?

Question

I am trying to add touch events from a file to the current application (build a new touch event according to the data found in the file ), and I am trying to understand the chain of calls when a "real" touch event is triggered.

From all the searches I conducted, I found that Activity.dispatchTouchEvent(ev) is the first method called when we have a touch event, then its forwarded to ViewGroup.dispatchTouchEvent and then to View.dispatchTouchEvent.

I want to find what is being called before Activity.dispatchTouchEvent(ev) and how the events is transferred from the HW to this method.

Answer 1

In Activty the method dispatchTouchEvent is :

 public boolean dispatchTouchEvent(MotionEvent ev) {
    if (ev.getAction() == MotionEvent.ACTION_DOWN) {
        onUserInteraction();
    }
    if (getWindow().superDispatchTouchEvent(ev)) {
        return true;
    }
    return onTouchEvent(ev);
}

you must call super.dispatchTouchEvent() method in ur own activity.

so that u can reach this line :getWindow().superDispatchTouchEvent(ev)

getWindwow() return the instance of PhoneWindow.

PhoneWindow.superDispatchTouchEvent() will call the DecorView's method ,and in that method ,DecorView.dispatchTouchEvent will be called.

So the event has been passed to the views.

    //in Class PhoneWindow
 public boolean superDispatchTouchEvent(MotionEvent event) {
      return mDecor.superDispatchTouchEvent(event);
 }

and

//in class DecorView
public boolean superDispatchTouchEvent(MotionEvent event) {
      return super.dispatchTouchEvent(event);
}

Answer 2

Maybe what you want is how android input framework works. The following blog about android input framework architecture may helps you.

Android Input Framework Architecture[Part 1] : Introduction to InputReader & InputDispatcher

The input process can simply be put as:

input hardware ------> kernel/driver(input protocol) -----> EventHub(framework/base/libs/ui) getevent------> InputReader ----> inputDispatcher ----> Window manager.

1. First, InputReader convert the meta input event to android event (etc. MotionEvent/KeyEvent).
2. Then, InputDispatcher dispatcher the event to WindowManager
3. WindowManager calls Window.Callback.dispatchTouchEvent(***).