beaconManager give me error when app back from background - ibeacon

Question

I use altbeacon library in my app. Everything work Ok after start, but if i out from app she's in background i get notification on statusbar about beacons. When i click on this notification i get this error:
Process: pl.hekko.kesser.beacontest, PID: 29929
java.lang.RuntimeException: Unable to start activity ComponentInfo{pl.hekko.kesser.beacontest/pl.hekko.kesser.beacontest.MainActivity}: java.lang.UnsupportedOperationException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2202)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2252)
at android.app.ActivityThread.access$800(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1200)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5103)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:606)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.UnsupportedOperationException
at java.util.Collections$UnmodifiableCollection.add(Collections.java:928)
at pl.hekko.kesser.beacontest.MainActivity.onCreate(MainActivity.java:83)
at android.app.Activity.performCreate(Activity.java:5275)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2166)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2252)
            at android.app.ActivityThread.access$800(ActivityThread.java:139)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1200)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
My MainActivity line 83:
beaconManager.getBeaconParsers().add(new BeaconParser().
setBeaconLayout("m:2-3=0215,i:4-19,i:20-21,i:22-23,p:24-24"));
I'm not sure this setBeaconLayout but seems to work fine generally.
Sometimes app doesn't start shows error, but second click on icon starts app. It seems that the same error cause this.

Answer 1

The problem is that you are only allowed to configure the list of active BeaconParsers once, when the library first starts up, so you get an error when you try to do it a second time. While it's easier to do this just once in the onCreate method of a custom Application, you can do this in the onCreate method of an Activity if you wrap it in an if statement like this:
// Only execute the code below if only the default BeaconParser is active
if (beaconManager.getBeaconParsers().size() == 1) {
// Put your BeaconParser setup code here
...
}