notification channels app crashes and stops-CodePudding

this is my code:

package com.rockykhan.notificationchannels;

import android.app.Application;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.os.Build;

public class app extends Application {

    // MAKING CHANNEL ID'S AS FINAL STRINGS
    public static final String CHANNEL_1_ID = "channel1";
    public static final String CHANNEL_2_ID = "channel2";

    @Override
    public void onCreate() {
        super.onCreate();

            if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {

                NotificationChannel channel1 = new NotificationChannel(CHANNEL_1_ID, "Channel 1", NotificationManager.IMPORTANCE_HIGH);
                NotificationChannel channel2 = new NotificationChannel(CHANNEL_2_ID, "Channel 2", NotificationManager.IMPORTANCE_LOW);

                channel1.setDescription("this is channel 1");
                channel2.setDescription("this is channel 2");

                NotificationManager manager = getSystemService(NotificationManager.class);
                manager.createNotificationChannel(channel1);
                manager.createNotificationChannel(channel2);
        }

    }
}

mainActivity:

package com.rockykhan.notificationchannels;

import static com.rockykhan.notificationchannels.app.CHANNEL_1_ID;
import static com.rockykhan.notificationchannels.app.CHANNEL_2_ID;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.NotificationCompat;
import androidx.core.app.NotificationManagerCompat;

import android.app.Notification;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

    EditText title, text;
    Button btn_c1, btn_c2;
    private NotificationManagerCompat notificationManager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        title.findViewById(R.id.notificationTitleText);
        text.findViewById(R.id.notificationMessageText);
        btn_c1.findViewById(R.id.sendNotificationThroughChannel1);
        btn_c2.findViewById(R.id.sendNotificationThroughChannel2);

        String notificationTitle = title.getText().toString();
        String notificationText = text.getText().toString();

        notificationManager = NotificationManagerCompat.from(this);

        btn_c1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                Notification notification = new NotificationCompat.Builder(MainActivity.this, CHANNEL_1_ID)
                        .setSmallIcon(R.drawable.imp_noti)
                        .setContentTitle(notificationTitle)
                        .setContentText(notificationText)
                        .setPriority(NotificationCompat.PRIORITY_HIGH)
                        .setCategory(NotificationCompat.CATEGORY_MESSAGE)
                        .build();

                notificationManager.notify(1, notification);

            }
        });
        btn_c2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                Notification notification = new NotificationCompat.Builder(MainActivity.this, CHANNEL_2_ID)
                        .setSmallIcon(R.drawable.noti)
                        .setContentTitle(notificationTitle)
                        .setContentText(notificationText)
                        .setPriority(NotificationCompat.PRIORITY_LOW)
                        .setCategory(NotificationCompat.CATEGORY_MESSAGE)
                        .build();

                notificationManager.notify(2, notification);

            }
        });

    }
}

xml:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@ id/sendNotificationThroughChannel2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Send on channel 2"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@ id/notificationTitleText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Title"
        android:inputType="textPersonName"
        android:minHeight="48dp"
        app:layout_constraintBottom_toTopOf="@ id/sendNotificationThroughChannel2"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@ id/sendNotificationThroughChannel1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Send on channel 1"
        app:layout_constraintBottom_toTopOf="@ id/sendNotificationThroughChannel2"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@ id/notificationMessageText" />

    <EditText
        android:id="@ id/notificationMessageText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Text"
        android:inputType="textPersonName"
        android:minHeight="48dp"
        app:layout_constraintBottom_toTopOf="@ id/sendNotificationThroughChannel1"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@ id/notificationTitleText" />
</androidx.constraintlayout.widget.ConstraintLayout>

logcat:

 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.rockykhan.notificationchannels/com.rockykhan.notificationchannels.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.widget.EditText.findViewById(int)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3408)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3547)

So I was trying to send notifications through buttons but the app doesn't seem to start. It crashes and as far as I thought, it was a problem in xml Id's but I can't find the main problem here ( I think it is something to do with the findViewbyId of the editText). Help will be much appreciated!

CodePudding user response：

Assign the result of calling findViewById() to your View variables, don't call findViewById() on the variables itself.

So basically replace these lines

title.findViewById(R.id.notificationTitleText);
text.findViewById(R.id.notificationMessageText);
btn_c1.findViewById(R.id.sendNotificationThroughChannel1);
btn_c2.findViewById(R.id.sendNotificationThroughChannel2);

with these

title = findViewById(R.id.notificationTitleText);
text = findViewById(R.id.notificationMessageText);
btn_c1 = findViewById(R.id.sendNotificationThroughChannel1);
btn_c2 = findViewById(R.id.sendNotificationThroughChannel2);