Trying to use AlertDialog but the app crashes at launch

Issue

I am trying to use AlertDialog widget in my app, but whatever I do the app crashes at launch. I know something is messed up or not defined but can't seem to find it.I have defined a button for triggering the alert dialog and set 'yes' and 'no' options for the dialog. Selecting 'yes' will result in exiting the app and showing a toast and Selecting 'no' will close the alert dialog and return to app by showing a toast. This is how it should work on paper but as I said the app will crash on launch. My code:

package com.example.togglebutton;

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

import android.content.DialogInterface;
import android.os.Bundle;
import android.view.View;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Button;
import android.widget.Toast;
import android.widget.ToggleButton;

public class MainActivity extends AppCompatActivity {

   private Button bt;
   AlertDialog.Builder builder;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        bt = (Button) findViewById(R.id.btn);
        builder = new AlertDialog.Builder(this);
        bt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                builder.setMessage("Do you want to close this application ?")
                        .setCancelable(false)
                        .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id, ) {
                                finish();
                                Toast.makeText(getApplicationContext(), "you chose yes",
                                        Toast.LENGTH_SHORT).show();
                            }
                        })
                        .setNegativeButton("No", new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id) {
                               
                                dialog.cancel();
                                Toast.makeText(getApplicationContext(), "you chose no ",
                                        Toast.LENGTH_SHORT).show();
                            }
                        });
                
                AlertDialog alert = builder.create();

                alert.setTitle("AlertDialogExample");
                alert.show();
            }


        });
}
}

Solution

SOLUTION OF YOUR PROBLEM

You need to set the layout of the activity and in the above-posted code what we can see that it is missing. So just add the line below super.onCreate(savedInstanceState);

setContentView(R.layout.YOUR_LAYOUT_NAME);

NOTE: Replace YOUR_LAYOUT_NAME with the name of the layout file which you have defined for MainActivity.

Answered By - Kamal Nayan