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Editorial Team
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Asked: 2026-05-27T00:35:36+00:00

I’m trying to understand what happens when a button is clicked in android. So

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I’m trying to understand what happens when a button is clicked in android. So I set up a couple of break points for a simple button click. The picture shows what happens when a button is clicked my questions are: (GUI generated events are events that are generated as a result of interaction with the gui for example Button Clicks, editing text etc…)

1- Is Looper.loop() the main loop for the application or the OS looper ?

2- Where does ViewRootImpl(handler).dispatchMessage(Message) reside? Application or OS?

3- Can I intercept GUI generated events in the main looper ? if yes then how?

4- Can we safely assume that all GUI generated events are handled in ViewRootImpl(handler).handleCallback(Message)?

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  1. Editorial Team

    Is Looper.loop() the main loop for the application or the OS looper ?

    I don’t know what you think the “OS looper” is. The Looper runs in your process, if that’s what you mean.

    Where does ViewRootImpl(handler).dispatchMessage(Message) reside? Application or OS?

    I don’t know what you think the “OS” is in this context. ViewRootImpl is a Dalvik-compiled class that is loaded into your Dalvik VM and its code executes within your process. Otherwise, you would not be able to see it in your stack trace.

    Can I intercept GUI generated events in the main looper ?

    Only by modifying the firmware to replace various classes like ViewRootImpl with your own code.

    Can we safely assume that all GUI generated events are handled in ViewRootImpl(handler).handleCallback(Message)?

    I certainly would not make that assumption. For example, not all applications use the widget framework (e.g., games).

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