Fix security exception in android 7 phones, bump version

Author: hoffimar

app/build.gradle

@@ -6,8 +6,8 @@ android {
         applicationId "com.tomatodev.timerdroid"
         minSdkVersion 18
         targetSdkVersion 26
-        versionCode 1412300
-        versionName "3.0.0"
+        versionCode 1412310
+        versionName "3.1.0"
         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
         vectorDrawables.useSupportLibrary = true
     }

app/src/main/AndroidManifest.xml

@@ -5,6 +5,7 @@
     <uses-permission android:name="android.permission.VIBRATE" />
     <uses-permission android:name="android.permission.WAKE_LOCK" />
     <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
+    <uses-permission android:name="android.permission.ACCESS_NOTIFICATION_POLICY" />
 
     <application
         android:allowBackup="true"

app/src/main/java/com/tomatodev/timerdroid/service/CustomNotificationManager.java

@@ -200,7 +200,7 @@ public void startNotificationForFinishedTimer(String timerName){
 
         // set alarm volume (API < 26)
         // TODO problem when 2 alarms go off after each other, will overwrite the system volume
-        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O){
+        if (canSetVolume()){
             mVolumeBefore = audio.getStreamVolume(SOUND_STREAM);
             int max = audio.getStreamMaxVolume(SOUND_STREAM);
             int volume = (int) Math.round(prefs.getInt("alarm_volume", 5) * 0.1 * max);
@@ -213,11 +213,26 @@ public void startNotificationForFinishedTimer(String timerName){
     }
 
     public void cancelSoundNotification(){
-        // reset alarm volume
-        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O ){
+        // reset alarm volume if allowed
+        if (canSetVolume()){
             mAudioManager.setStreamVolume(AudioManager.STREAM_ALARM, mVolumeBefore, 0);
             mAudioManager.setRingerMode(mRingerModeBefore);
         }
+
         mNotificationManager.cancel(NOTIFICATION_ID_FINISHED);
     }
+
+    private boolean canSetVolume(){
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O ) {
+            return false;
+        }
+
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
+            if (!mNotificationManager.isNotificationPolicyAccessGranted()) {
+                return false;
+            }
+        }
+
+        return true;
+    }
 }

app/src/main/res/values/strings.xml

@@ -20,7 +20,7 @@
     <string name="about_author_label">Author</string>
     <string name="about_author" translatable="false">Martin Hoffmann</string>
     <string name="about_version_label">Version</string>
-    <string name="about_version" translatable="false">3.0.0</string>
+    <string name="about_version" translatable="false">3.1.0</string>
     <string name="about_link"><a href="https://github.com/hoffimar/timerdroid">Website</a></string>
     <string name="menu_about_button_text">OK</string>