Layouts and Views

Views and layouts

A View is a single UI element (text, button, image). A layout is a container that arranges views. You describe them in XML files under res/layout/.

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Welcome!" />

    <Button
        android:id="@+id/loginBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Log in" />
</LinearLayout>

Reacting to a click

findViewById<Button>(R.id.loginBtn).setOnClickListener {
    Toast.makeText(this, "Clicked!", Toast.LENGTH_SHORT).show()
}

Common layouts

• LinearLayout — stack views in a row or column.
• ConstraintLayout — position views relative to each other (best for complex screens).
• RecyclerView — show long, scrolling lists efficiently.