Android Studio 3.2.1: Silent Mode Toggle app crashes when clicked even though no error in code - android-studio

Question

I'm just starting to learn coding for Android App by following the book Android App Development for Dummies to create the Silent Mode Toggle App.
Everything seems fine in the code (no error except for warning that:
"Casting 'findViewById(R.id.phone_icon)' to 'ImageView' is redundant.
This inspection reports unnecessary cast expressions."
I have read through a similar problem here (Application Crashes - Silent Mode Toggle - Android for Dummies) and it says to try:
1) Change "extends ActionBarActivity" to just "extends Activity" and import - mine is already as such.
2) delete or comment the 'if' in the onCreate method out - mine don't have this section.
3) change the parameter of the setContentView to: R.layout.fragment_main - not very sure what this means but don't seem to be relevant to my code? (his codes and mine are slightly different)
MainActivity.java Code
package com.dummies.silentmodetoggle;
import android.app.Activity;
import android.media.AudioManager;
import android.os.Bundle;
import android.view.View;
import android.widget.FrameLayout;
import android.widget.ImageView;
import com.dummies.silentmodetoggle.util.RingerHelper;
public class MainActivity extends Activity {
AudioManager audioManager;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
audioManager = (AudioManager) getSystemService(AUDIO_SERVICE);
setContentView(R.layout.activity_main);
FrameLayout contentView =
(FrameLayout) findViewById(R.id.content);
contentView.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
RingerHelper.performToggle(audioManager);
updateUi();
}
});
}
private void updateUi() {
ImageView imageView = (ImageView) findViewById(R.id.phone_icon);
int phoneImage = RingerHelper.isPhoneSilent(audioManager)
? R.mipmap.ringer_off
: R.mipmap.ringer_on;
imageView.setImageResource(phoneImage);
}
#Override
protected void onResume(){
super.onResume();
// Update our UI in case anything has changed.
updateUi();
}
}
RingerHelper.java
The book says to create a java file at: "src/main/java/com/dummies/silentmodetoggle/util/RingerHelper.java" but did not state how. Since I do not have a util folder so I'd created a package (New>Package) at "src/main/java/com.dummies.silentmodetoggle" and added the RingerHelper java file in the util folder. Note sure if this is the problem? The code is as below:
package com.dummies.silentmodetoggle.util;
import android.media.AudioManager;
public class RingerHelper {
// private to prevent users from creating a RingerHelper object
private RingerHelper(){}
/* Toggles the phone's silent mode */
public static void performToggle(AudioManager audioManager) {
// If the phone is currently silent, then unsilence it. If
// it's currently normal, then silence it.
audioManager.setRingerMode(
isPhoneSilent(audioManager)
? AudioManager.RINGER_MODE_NORMAL
: AudioManager.RINGER_MODE_SILENT);
}
/* Returns whether the phone is currently in silent mode. */
public static boolean isPhoneSilent(AudioManager audioManager){
return audioManager.getRingerMode()
== AudioManager.RINGER_MODE_SILENT;
}
}
Error from LogCat when I clicked the button on app
2018-12-01 22:11:44.029 30122-30122/com.dummies.silentmodetoggle E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.dummies.silentmodetoggle, PID: 30122
java.lang.SecurityException: Not allowed to change Do Not Disturb state
at android.os.Parcel.readException(Parcel.java:1683)
at android.os.Parcel.readException(Parcel.java:1636)
at android.media.IAudioService$Stub$Proxy.setRingerModeExternal(IAudioService.java:962)
at android.media.AudioManager.setRingerMode(AudioManager.java:1022)
at com.dummies.silentmodetoggle.util.RingerHelper.performToggle(RingerHelper.java:13)
at com.dummies.silentmodetoggle.MainActivity$1.onClick(MainActivity.java:60)
at android.view.View.performClick(View.java:5610)
at android.view.View$PerformClick.run(View.java:22265)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
2018-12-01 22:11:44.672 1315-1315/? E/EGL_emulation: tid 1315: eglCreateSyncKHR(1901): error 0x3004 (EGL_BAD_ATTRIBUTE)
Otherwise the app seems to work fine, ie, when I click on the volume button of the device itself to silent, the app image will change to silent and vice versa. It just crashes when I try to click on the image of the app itself.
I really have no idea what's going on. Please help. Thanks very much!

Answer 1

You need to add permissions for Do Not Disturb State. I was facing the same issue and I added the following lines to my Main_Activity.java code in onCreate method and it works fine Now:
NotificationManager notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
if(notificationManager.isNotificationPolicyAccessGranted())
{
Intent intent = new Intent(android.provider.Settings.ACTION_NOTIFICATION_POLICY_ACCESS_SETTINGS);
startActivity(intent);
}