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.

Why do you have to simulate the actual touch event? Can you just call the code that would be called by the touch event instead? — GLee, Dec 16 '13 at 18:30
I want to control one device by another device,I build a connection which transfers the events from the controlling device via WIFI-p2p to the controlled device, saves them in a file in a specific format, and then on the controlled device I need to read the events from the file, build event objects and inject them somehow to the currently running application without changing the application and without assuming I know the code of this app. So that is why I cant call the code of the app, I want to catch the method which calls to Activity.dispatchTouchEvent and try to mess with the code there — Foad Rezek, Dec 16 '13 at 18:35

chaman · Answer 1 · 2020-01-02T03:38:21.553

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.

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

score 2 · Answer 2 · edited Nov 21 '18 at 10:05

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);
}

who calls Activity.dispatchTouchEvent( event )?

2 Answers2