Is it mandatory to create a copy of View before assigning an event handler in Android in Kotlin

Question

I am trying to set OnClickListener on an Android button in Kotlin file. Unlike java file, where I can declare button variable at the class level and initialize it in onCreate method and assign ClickListener at the same time as:

Button inlineButton;
    @Override
    public void onCreate(@Nullable Bundle savedInstanceState, @Nullable PersistableBundle persistentState) {
        super.onCreate(savedInstanceState, persistentState);
        inlineButton = findViewById(R.id.btn_inline);
        inlineButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                new NotificationToast(MainActivity.this, "Inline Button");
            }
        });
    }

when I try to follow similar pattern I get an error with the following message:

I can only set the event handler only when I create a copy of button with following code:

var inlineButton : Button? = null;

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    inlineButton = findViewById(R.id.btn_inline)
    val inlineButtonCopy = inlineButton;

    if (inlineButtonCopy != null) {
        inlineButtonCopy.setOnClickListener({
            NotificationToast(this,inlineButtonCopy.text.toString()).Show();
        })
    }

}

I was wondering if it is not possible to create only a single instance of Button on top level, initialize it in oncreate, and set event handler. If I can create only a single instance, I can use the event to change the property of the same button. Is it the default behavior or am I missing something.

Any clarification is highly appreciated.

Answer 1

In Kotlin you don't need to define the Id's of the XML component.
you can directly access with the help of Id's are already defined in your XML.

let suppose you defined the Button Id in XML is btn_inline

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    btn_inline.setOnClickListener({
        NotificationToast(this,inlineButtonCopy.text.toString()).Show();
    })
}

Also, make sure that something like this should be present there in the import section.

import kotlinx.android.synthetic.main.activity_main.*

Just check at your end.