TextView, EditText और Button

<TextView
    android:id="@+id/tvWelcome"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="@string/welcome"
    android:textSize="20sp"
    android:textStyle="bold"
    android:textColor="@color/brand"
    android:gravity="center"
    android:maxLines="2"
    android:ellipsize="end"
    android:drawablePadding="8dp"
    android:drawableStart="@drawable/ic_star" />

<!-- res/values/strings.xml -->
<resources>
    <string name="app_name">BMI Calculator</string>
    <string name="welcome">Welcome to BMI Calculator</string>
    <string name="your_bmi">Your BMI is %1$.1f (%2$s)</string>
</resources>

// Kotlin
tvResult.text = getString(R.string.your_bmi, 22.7, "Normal")   // "Your BMI is 22.7 (Normal)"

<EditText
    android:id="@+id/etWeight"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="Weight in kg"
    android:inputType="numberDecimal"
    android:maxLength="5"
    android:imeOptions="actionNext" />

<com.google.android.material.textfield.TextInputLayout
    android:id="@+id/tilHeight"
    style="@style/Widget.Material3.TextInputLayout.OutlinedBox"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="Height in cm"
    app:helperText="Example: 165"
    app:suffixText="cm">

    <com.google.android.material.textfield.TextInputEditText
        android:id="@+id/etHeight"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="number"
        android:imeOptions="actionDone" />
</com.google.android.material.textfield.TextInputLayout>

<!-- password with eye icon -->
<com.google.android.material.textfield.TextInputLayout
    style="@style/Widget.Material3.TextInputLayout.OutlinedBox"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="Password"
    app:endIconMode="password_toggle">

    <com.google.android.material.textfield.TextInputEditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textPassword" />
</com.google.android.material.textfield.TextInputLayout>

// 1) lambda (most common)
btnCalculate.setOnClickListener { calculate() }

// 2) long press
btnCalculate.setOnLongClickListener {
    Toast.makeText(this, "Tap to calculate", Toast.LENGTH_SHORT).show()
    true                                  // true = event handled
}

// 3) enable / disable
btnCalculate.isEnabled = false

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="24dp">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/welcome"
        android:textSize="22sp"
        android:textStyle="bold" />

    <com.google.android.material.textfield.TextInputLayout
        android:id="@+id/tilWeight"
        style="@style/Widget.Material3.TextInputLayout.OutlinedBox"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:hint="Weight"
        app:suffixText="kg">

        <com.google.android.material.textfield.TextInputEditText
            android:id="@+id/etWeight"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:inputType="numberDecimal" />
    </com.google.android.material.textfield.TextInputLayout>

    <com.google.android.material.textfield.TextInputLayout
        android:id="@+id/tilHeight"
        style="@style/Widget.Material3.TextInputLayout.OutlinedBox"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="12dp"
        android:hint="Height"
        app:suffixText="cm">

        <com.google.android.material.textfield.TextInputEditText
            android:id="@+id/etHeight"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:imeOptions="actionDone"
            android:inputType="number" />
    </com.google.android.material.textfield.TextInputLayout>

    <Button
        android:id="@+id/btnCalculate"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp"
        android:text="Calculate BMI" />

    <TextView
        android:id="@+id/tvResult"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="24dp"
        android:gravity="center"
        android:textSize="20sp" />
</LinearLayout>

package com.example.bmi

import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import com.google.android.material.textfield.TextInputEditText
import com.google.android.material.textfield.TextInputLayout

class MainActivity : AppCompatActivity() {

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

        val tilWeight = findViewById<TextInputLayout>(R.id.tilWeight)
        val tilHeight = findViewById<TextInputLayout>(R.id.tilHeight)
        val etWeight = findViewById<TextInputEditText>(R.id.etWeight)
        val etHeight = findViewById<TextInputEditText>(R.id.etHeight)
        val tvResult = findViewById<TextView>(R.id.tvResult)

        findViewById<Button>(R.id.btnCalculate).setOnClickListener {
            val weight = etWeight.text?.toString()?.toDoubleOrNull()
            val heightCm = etHeight.text?.toString()?.toDoubleOrNull()

            tilWeight.error = if (weight == null || weight <= 0) "Enter weight" else null
            tilHeight.error = if (heightCm == null || heightCm < 50) "Enter height in cm" else null
            if (tilWeight.error != null || tilHeight.error != null) return@setOnClickListener

            val h = heightCm!! / 100
            val bmi = weight!! / (h * h)
            val category = when {
                bmi < 18.5 -> "Underweight"
                bmi < 25 -> "Normal"
                bmi < 30 -> "Overweight"
                else -> "Obese"
            }
            tvResult.text = getString(R.string.your_bmi, bmi, category)
        }
    }
}