Invoking callback function

The documentation describes how to create a callback function object wrapper. The documentation I'm following comes from page 18 of the Monkey C Programmers Guide. It reads...

If you want to create a callback, you can create a Method object. Method objects are a combination of the function and the object instance or module they originate from. You can then call the method using the invoke method.

// Handle completion of long function wakeMeUpBeforeYouGoGo() { // Do something here } // Create a call back with the method method (jinx!) doLongRunningTask(method(:wakeMeUpBeforeYouGoGo));

I've tried several times, and I'm unable to figure out what I need to do to be able to invoke the passed callback.

using Toybox.WatchUi as Ui;

using Toybox.System as Sys;



class TestView extends Ui.DataField {



    function onLayout(dc) {

    }



    function onShow() {

    }



    function compute(info) {

    }



    function doLongRunningTask(fn) {

        invoke(fn); // what to do here?

    }



    function wakeMeUpBeforeYouGoGo() {

        Sys.println("!");

    }



    //! Update the view

    function onUpdate(dc) {

       doLongRunningTask(method(:wakeMeUpBeforeYouGoGo));

    }

}

travis.vitek over 10 years ago

Nevermind. I figured it out. The method function creates a Toybox.Lang.Method object, which has an invoke() method on it. So the syntax to invoke the method object fn in the above example is...

function doLongRunningTask(fn) {
    fn.invoke();
}

If you'd like to invoke the method with parameters, you just pass them to the invoke method, like this...

fn.invoke(1);
    fn.invoke("Hello");

Former Member over 9 years ago

Nevermind. I figured it out. The method function creates a Toybox.Lang.Method object, which has an invoke() method on it. So the syntax to invoke the method object fn in the above example is...

function doLongRunningTask(fn) { fn.invoke(); }

If you'd like to invoke the method with parameters, you just pass them to the invoke method, like this...

fn.invoke(1); fn.invoke("Hello");

I've tried it, but it does not work. Error Message: "Could not find symbol method." in line "doLongRunningTask(method(:wakeMeUpBeforeYouGoGo));". What's going wrong??

travis.vitek over 9 years ago

It works just fine. There is something wrong with your code.

Given the error message, the place that you are calling method is probably a context where there is no object (i.e., not a function of a class). In that case, you need to tell the system what object you want to invoke the function on by qualifying the call with an object reference (obj.method(:wakeMeUpBeforeYouGoGo) will create a Lang.Method that, when invoked, will call obj.wakeMeUpBeforeYouGoGo()).

Travis

Former Member over 9 years ago

Thank you very much! Your tip pointed me in the right direction. In my case it was a function of a module. A "new Lang.Method(ModuleName, :functionOfModul)" did the trick.