Here is a short guide to use buttons and textView in kotlin android. If you’re a java dev who is trying to switch to kotlin then this guide is made for you. If you’re a new to android development then refer to Google Developers.

Start by creating a button in layout like you do usually :

<Button
        android:id="@+id/toast_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:text="Toast Button" />

I gave it an ID of toast_buttonso that we can reference it in code. Now navigate to the kotlin file of that activity or fragment.

        val toastButton = findViewById<Button>(R.id.toast_button)

This is how we reference a button object in kotlin. Let me compare it to java for you.

        Button toastButton = (Button) findViewById(R.id.toast_button);

No much difference right ? remember that val in kotlin cannot be reassigned. That means it’s similar to final object in java. So bascially the kotlin code above is :

        final Button toastButton = (Button) findViewById(R.id.toast_button);

Which cannot be reassigned again. What if you want it to change. In that case use var instead of val.

var age = 3
age = 5
age = 7

var can be reassigned but if you try to reassign val you’ll get a warning ⚠ saying that val cannot be reassigned.

button-kotlin-fundamental-01