Add configurable behavior of the back button

This PR allows users to change how the back button functions. Closes #2196

Possible choices are following:

 - **Default** - back button functions how it currently functions (closes the app if there is nowhere to go back to)

 - **Open navigation drawer** - back button always opens the navigation drawer instead of closing the app

 - **Double tap to exit** - like default, but requires two taps to close the app

 - **Confirm to exit** - like default, but prompts user if they really want to exit

3 files changed, 38 insertions, 0 deletions

diff --git a/core/src/main/java/de/danoeh/antennapod/core/preferences/UserPreferences.java b/core/src/main/java/de/danoeh/antennapod/core/preferences/UserPreferences.java
index e6b5f9e1b..c80cfacba 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/preferences/UserPreferences.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/preferences/UserPreferences.java
@@ -52,6 +52,7 @@ public class UserPreferences {
     public static final String PREF_COMPACT_NOTIFICATION_BUTTONS = "prefCompactNotificationButtons";
     public static final String PREF_LOCKSCREEN_BACKGROUND = "prefLockscreenBackground";
     private static final String PREF_SHOW_DOWNLOAD_REPORT = "prefShowDownloadReport";
+    private static final String PREF_BACK_BUTTON_BEHAVIOR = "prefBackButtonBehavior";
 
     // Queue
     private static final String PREF_QUEUE_ADD_TO_FRONT = "prefQueueAddToFront";
@@ -809,4 +810,18 @@ public class UserPreferences {
     public enum VideoBackgroundBehavior {
         STOP, PICTURE_IN_PICTURE, CONTINUE_PLAYING
     }
+
+    public enum BackButtonBehavior {
+        DEFAULT, OPEN_DRAWER, DOUBLE_TAP, SHOW_PROMPT
+    }
+
+    public static BackButtonBehavior getBackButtonBehavior() {
+        switch (prefs.getString(PREF_BACK_BUTTON_BEHAVIOR, "default")) {
+            case "default": return BackButtonBehavior.DEFAULT;
+            case "drawer": return BackButtonBehavior.OPEN_DRAWER;
+            case "doubletap": return BackButtonBehavior.DOUBLE_TAP;
+            case "prompt": return BackButtonBehavior.SHOW_PROMPT;
+            default: return BackButtonBehavior.DEFAULT;
+        }
+    }
 }
diff --git a/core/src/main/res/values/arrays.xml b/core/src/main/res/values/arrays.xml
index 7e2fed054..2d84cbd70 100644
--- a/core/src/main/res/values/arrays.xml
+++ b/core/src/main/res/values/arrays.xml
@@ -277,4 +277,18 @@
         <item>@string/select_all_above</item>
         <item>@string/select_all_below</item>
     </string-array>
+
+    <string-array name="back_button_behavior_options">
+        <item>@string/back_button_default</item>
+        <item>@string/back_button_open_drawer</item>
+        <item>@string/back_button_double_tap</item>
+        <item>@string/back_button_show_prompt</item>
+    </string-array>
+
+    <string-array name="back_button_behavior_values">
+        <item>default</item>
+        <item>drawer</item>
+        <item>doubletap</item>
+        <item>prompt</item>
+    </string-array>
 </resources>
diff --git a/core/src/main/res/values/strings.xml b/core/src/main/res/values/strings.xml
index ad91ecc76..fd5535462 100644
--- a/core/src/main/res/values/strings.xml
+++ b/core/src/main/res/values/strings.xml
@@ -470,6 +470,15 @@
     <string name="pref_videoBehavior_sum">Behavior when leaving video playback</string>
     <string name="stop_playback">Stop playback</string>
     <string name="continue_playback">Continue audio playback</string>
+    <string name="behavior">Behavior</string>
+    <string name="pref_back_button_behavior_title">Back button behavior</string>
+    <string name="pref_back_button_behavior_sum">Change behavior of the back button.</string>
+    <string name="back_button_default">Default</string>
+    <string name="back_button_open_drawer">Open navigation drawer</string>
+    <string name="back_button_double_tap">Double tap to exit</string>
+    <string name="back_button_show_prompt">Confirm to exit</string>
+    <string name="close_prompt">Are you sure you want to close AntennaPod?</string>
+    <string name="double_tap_toast">Tap back button again to exit</string>
 
     <!-- Auto-Flattr dialog -->
     <string name="auto_flattr_enable">Enable automatic flattring</string>