R.id.main giving me a red error, cannot resolve symbol main in MainActivity.java

Question

I'm using Android Studio for the first time. I'm following a tutorial online to build a calculator, and I'm trying to run my program through the emulator. But when I run it, I get the error message, "Cannot find symbol variable id".

I read through a lot of questions and answers trying to find the exact problem, but the closest I found was that in "R.id.main", the 'main' part should be somehow tied to my activity_main file, but I don't know how. I know some were saying to use "android:id" but in the tutorial, the instructor hadn't done anything with ids yet. So I don't know if it's because I somehow saved a file in a wrong folder.

I tried doing a Clean Build as I saw in one solution to someone else's related issue, but it didn't help. The program just gave the same error. Here is the compiler error:

C:\Users\using\Desktop\Android Projects\BMICalculator\app\src\main\java\com\miramichelle\bmicalculator\MainActivity.java:18: error: cannot find symbol
        ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
                                                                ^
  symbol:   variable id
  location: class R

My code is:

MainActivity.java

package com.miramichelle.bmicalculator;

import android.os.Bundle;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EdgeToEdge.enable(this);
        setContentView(R.layout.activity_main);
        ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
            Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
            v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
            return insets;
        });
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center_horizontal"
    android:orientation="vertical">

    <ImageView
        android:layout_width="100dp"
        android:layout_height="100dp"
        />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="BMI Calculator" />

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Male" />

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Female" />

    </LinearLayout>

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:hint="Age" />

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <EditText
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:hint="Feet" />

        <EditText
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:hint="Inches" />
    </LinearLayout>

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:hint="Weight (kg)" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="calculate" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="23.6" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="You are a healthy weight!" />
</LinearLayout>

Answer 1

In the layout file (activity_main.xml) you should set android:id="@+id/main" to a view you're interested in, most likely for LinearLayout.