Bdtjtk

I am beginner in programing, and I know how btn.setOnClickListener{} function works (curly brackets).
But there is other tipe of function btn.setOnClickListener() - brackets are not curly. I do not know how and when I should use this tipe of functions. How does such type of function calls? I would like to learn more about it but I do not know how to google it
Answer: "If a function has only one parameter, and this is a function, the parentheses can be deleted"

According to : https://antonioleiva.com/lambdas-kotlin-android/

If a function has only one parameter, and this is a function, the parentheses can be deleted



Instead of having empty parentheses, we can better delete them:

view.setOnClickListener { v -> toast("Hello") }

If the function’s last parameter is a function, it can go outside the parentheses



Therefore, we can extract the listener as follows:

view.setOnClickListener() { v -> toast("Hello") }

If we had more parameters, the rest of the parameters would go inside the parentheses, even if these were functions. Only the last parameter can be extracted.

Both types are equivalent:

button.setOnClickListener {

    // ......................

}



button.setOnClickListener(View.OnClickListener {

    // ......................

})

but the 1st one is the preferred way to go.

Even if you write the 2nd one, if you hover the mouse over View.OnClickListener,
Android Studio will pop up this message:

Redundant SAM constructor

and if you press Alt-Enter you will be prompted:

Remove redundant SAM constructor

and if you click on it then View.OnClickListener will be removed.

Again by pressing Alt-Enter you will be prompted:

Move lambda argument out of parentheses

and if you click on it then you will get the 1st type.

So don't worry about it, use the 1st type and you will be fine.

Answer: "If a function has only one parameter, and this is a function, the parentheses can be deleted"

setOnClickListener(Interface i)

 This is Method of View Class in Android.

1. setOnClickListener is method of that class which except only interface as a parameter.



2. or else you have to implement that interface in your class like given example.



Go through Anonymous Class implement process.



the thing is that.  either you pass interface object or you have to implement onClick method  interface OnClickListener.









1. When you want to implement in class  use this



    btnView.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {



            }

        });





2. Pass interface object of onClickListener



        appView.setOnClickListener();  ;----> pass interface object