I am new to Android programming and I am just beginning to learn, which I am learning little by little by tinkering around, as well as using the knowledge I have had with Java.
I want to create a notification class to hold all notification methods to call from at any time I'd like to make a notification occur. For some reason, I am having an exception while the program is creating a NotificationManager object to make a notification channel. This only seems to happen when making the notification class a separate class.
MainActivity Class:
package com.example.colombian.textingclasses;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
notifications n = new notifications(this);
}
}
notifications class:
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.content.Context;
import android.os.Build;
import android.support.v7.app.AppCompatActivity;
public class notifications {
private Context context;
public final String CHANNEL_ID = "customChannel";
public notifications(Context c) {
createNotificationChannel();
context = c;
}
//creates a notification channel
private void createNotificationChannel() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
CharSequence name = "MyChannel";
String description = "Description";
int importance = NotificationManager.IMPORTANCE_HIGH;
NotificationChannel channel = new NotificationChannel(CHANNEL_ID, name, importance);
channel.setDescription(description);
/*******Error happens below*******/
NotificationManager nm = (NotificationManager) context.getSystemService(NotificationManager.class); //error
nm.createNotificationChannel(channel);
}
}
}
Exception:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.colombian.textingclasses, PID: 16471
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.colombian.textingclasses/com.example.colombian.textingclasses.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.Class)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2957)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3032)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6940)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.Class)' on a null object reference
at com.example.colombian.textingclasses.notifications.createNotificationChannel(notifications.java:32)
at com.example.colombian.textingclasses.notifications.<init>(notifications.java:19)
at com.example.colombian.textingclasses.MainActivity.onCreate(MainActivity.java:14)
at android.app.Activity.performCreate(Activity.java:7174)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1220)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2910)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3032)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6940)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)
Strange thing is, when the createNotificationChannel() method is within the MainActivity class, it works perfectly fine. It even seems to work if I make the notification class an inner class of MainActivity. I just do not understand why there is an exception when I copy it to a separate class to create an object from.
Keep in mind, this based on API 26+ or Android 8.0.0
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P.S. I hope my question is specific enough. This is my first time asking a question on here so please let me know if there is something that needs more clarification. Thanks.
