Implement alternative approach to veto-able back buttons.

// FREEBIE

Signal.xcodeproj/project.pbxproj

@@ -74,6 +74,7 @@
 		34B3F89C1E8DF3270035BE1A /* BlockListViewController.m in Sources */ = {isa = PBXBuildFile; fileRef = 34B3F89B1E8DF3270035BE1A /* BlockListViewController.m */; };
 		34B3F89F1E8DF5490035BE1A /* OWSTableViewController.m in Sources */ = {isa = PBXBuildFile; fileRef = 34B3F89E1E8DF5490035BE1A /* OWSTableViewController.m */; };
 		34B3F8A21E8EA6040035BE1A /* ViewControllerUtils.m in Sources */ = {isa = PBXBuildFile; fileRef = 34B3F8A11E8EA6040035BE1A /* ViewControllerUtils.m */; };
+		34C42D5B1F45F7A80072EC04 /* OWSNavigationController.m in Sources */ = {isa = PBXBuildFile; fileRef = 34C42D5A1F45F7A80072EC04 /* OWSNavigationController.m */; };
 		34CCAF381F0C0599004084F4 /* AppUpdateNag.m in Sources */ = {isa = PBXBuildFile; fileRef = 34CCAF371F0C0599004084F4 /* AppUpdateNag.m */; };
 		34CCAF3B1F0C2748004084F4 /* OWSAddToContactViewController.m in Sources */ = {isa = PBXBuildFile; fileRef = 34CCAF3A1F0C2748004084F4 /* OWSAddToContactViewController.m */; };
 		34CE88E71F2FB9A10098030F /* ProfileViewController.m in Sources */ = {isa = PBXBuildFile; fileRef = 34CE88E61F2FB9A10098030F /* ProfileViewController.m */; };
@@ -505,6 +506,8 @@
 		34B3F89E1E8DF5490035BE1A /* OWSTableViewController.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = OWSTableViewController.m; sourceTree = "<group>"; };
 		34B3F8A01E8EA6040035BE1A /* ViewControllerUtils.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ViewControllerUtils.h; sourceTree = "<group>"; };
 		34B3F8A11E8EA6040035BE1A /* ViewControllerUtils.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = ViewControllerUtils.m; sourceTree = "<group>"; };
+		34C42D591F45F7A80072EC04 /* OWSNavigationController.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = OWSNavigationController.h; sourceTree = "<group>"; };
+		34C42D5A1F45F7A80072EC04 /* OWSNavigationController.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = OWSNavigationController.m; sourceTree = "<group>"; };
 		34CCAF361F0C0599004084F4 /* AppUpdateNag.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = AppUpdateNag.h; sourceTree = "<group>"; };
 		34CCAF371F0C0599004084F4 /* AppUpdateNag.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = AppUpdateNag.m; sourceTree = "<group>"; };
 		34CCAF391F0C2748004084F4 /* OWSAddToContactViewController.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = OWSAddToContactViewController.h; sourceTree = "<group>"; };
@@ -1026,6 +1029,8 @@
 				34B3F85F1E8DF1700035BE1A /* OWSLinkedDevicesTableViewController.h */,
 				34B3F8601E8DF1700035BE1A /* OWSLinkedDevicesTableViewController.m */,
 				34B3F8611E8DF1700035BE1A /* OWSMessagesToolbarContentView.xib */,
+				34C42D591F45F7A80072EC04 /* OWSNavigationController.h */,
+				34C42D5A1F45F7A80072EC04 /* OWSNavigationController.m */,
 				34B3F8621E8DF1700035BE1A /* OWSQRCodeScanningViewController.h */,
 				34B3F8631E8DF1700035BE1A /* OWSQRCodeScanningViewController.m */,
 				34B3F89D1E8DF5490035BE1A /* OWSTableViewController.h */,
@@ -2307,6 +2312,7 @@
 				341BB7491DB727EE001E2975 /* JSQMediaItem+OWS.m in Sources */,
 				34B3F89C1E8DF3270035BE1A /* BlockListViewController.m in Sources */,
 				45F2B1941D9C9F48000D2C69 /* OWSOutgoingMessageCollectionViewCell.m in Sources */,
+				34C42D5B1F45F7A80072EC04 /* OWSNavigationController.m in Sources */,
 				BFB074C919A5611000F2947C /* ObservableValue.m in Sources */,
 				B68EF9BA1C0B1EBD009C3DCD /* FLAnimatedImage.m in Sources */,
 				B68112EA1A4D9EC400BA82FF /* UIImage+normalizeImage.m in Sources */,

Signal/src/AppDelegate.m

@@ -11,6 +11,7 @@
 #import "NotificationsManager.h"
 #import "OWSContactsManager.h"
 #import "OWSContactsSyncing.h"
+#import "OWSNavigationController.h"
 #import "OWSProfileManager.h"
 #import "OWSStaleNotificationObserver.h"
 #import "Pastelog.h"
@@ -802,8 +803,8 @@ static NSString *const kURLHostVerifyPrefix             = @"verify";
         self.window.rootViewController = navigationController;
     } else {
         RegistrationViewController *viewController = [RegistrationViewController new];
-        UINavigationController *navigationController =
+        OWSNavigationController *navigationController =
-            [[UINavigationController alloc] initWithRootViewController:viewController];
+            [[OWSNavigationController alloc] initWithRootViewController:viewController];
         navigationController.navigationBarHidden = YES;
         self.window.rootViewController = navigationController;
     }

Signal/src/ViewControllers/NewGroupViewController.m

@@ -10,6 +10,7 @@
 #import "ContactsViewHelper.h"
 #import "Environment.h"
 #import "OWSContactsManager.h"
+#import "OWSNavigationController.h"
 #import "OWSTableViewController.h"
 #import "Signal-Swift.h"
 #import "SignalKeyingStorage.h"
@@ -34,7 +35,8 @@ const NSUInteger kNewGroupViewControllerAvatarWidth = 68;
     AvatarViewHelperDelegate,
     AddToGroupViewControllerDelegate,
     OWSTableViewControllerDelegate,
-    UINavigationControllerDelegate>
+    UINavigationControllerDelegate,
+    OWSNavigationView>
 
 @property (nonatomic, readonly) OWSMessageSender *messageSender;
 @property (nonatomic, readonly) ContactsViewHelper *contactsViewHelper;
@@ -97,8 +99,6 @@ const NSUInteger kNewGroupViewControllerAvatarWidth = 68;
     [super loadView];
 
     self.title = NSLocalizedString(@"NEW_GROUP_DEFAULT_TITLE", @"The navbar title for the 'new group' view.");
-    self.navigationItem.leftBarButtonItem =
-        [self createOWSBackButtonWithTarget:self selector:@selector(backButtonPressed:)];
 
     self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc]
         initWithTitle:NSLocalizedString(@"NEW_GROUP_CREATE_BUTTON", @"The title for the 'create group' button.")
@@ -547,7 +547,7 @@ const NSUInteger kNewGroupViewControllerAvatarWidth = 68;
 
 #pragma mark - Event Handling
 
-- (void)backButtonPressed:(id)sender
+- (void)backButtonPressed
 {
     [self.groupNameTextField resignFirstResponder];
 
@@ -649,6 +649,13 @@ const NSUInteger kNewGroupViewControllerAvatarWidth = 68;
     return [self.memberRecipientIds containsObject:recipientId];
 }
 
+#pragma mark - OWSNavigationView
+
+- (void)navBackButtonPressed
+{
+    [self backButtonPressed];
+}
+
 @end
 
 NS_ASSUME_NONNULL_END

Signal/src/ViewControllers/OWSConversationSettingsViewController.m

@@ -827,10 +827,7 @@ NS_ASSUME_NONNULL_BEGIN
     updateGroupViewController.conversationSettingsViewDelegate = self.conversationSettingsViewDelegate;
     updateGroupViewController.thread = (TSGroupThread *)self.thread;
     updateGroupViewController.mode = mode;
-
+    [self.navigationController pushViewController:updateGroupViewController animated:YES];
-    UINavigationController *navigationController =
-        [[UINavigationController alloc] initWithRootViewController:updateGroupViewController];
-    [self presentViewController:navigationController animated:YES completion:nil];
 }
 
 - (void)presentContactViewController

Signal/src/ViewControllers/OWSNavigationController.h

@@ -0,0 +1,20 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
+#import <UIKit/UIKit.h>
+
+@protocol OWSNavigationView <NSObject>
+
+- (void)navBackButtonPressed;
+
+@end
+
+#pragma mark -
+
+// This navigation controller subclass should be used anywhere we might
+// want to cancel back button presses or back gestures due to, for example,
+// unsaved changes.
+@interface OWSNavigationController : UINavigationController
+
+@end

Signal/src/ViewControllers/OWSNavigationController.m

@@ -0,0 +1,37 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
+#import "OWSNavigationController.h"
+
+@interface OWSNavigationController ()
+
+@end
+
+#pragma mark -
+
+@implementation OWSNavigationController
+
+- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item
+{
+
+    UIViewController *topViewController = self.topViewController;
+    BOOL wasBackButtonClicked = topViewController.navigationItem == item;
+
+    if (wasBackButtonClicked) {
+        if ([topViewController respondsToSelector:@selector(navBackButtonPressed)]) {
+            // if user did press back on the view controller where you handle the navBackButtonPressed
+            [topViewController performSelector:@selector(navBackButtonPressed)];
+            return NO;
+        } else {
+            // if user did press back but you are not on the view controller that can handle the navBackButtonPressed
+            [self popViewControllerAnimated:YES];
+            return YES;
+        }
+    } else {
+        // when you call popViewController programmatically you do not want to pop it twice
+        return YES;
+    }
+}
+
+@end

Signal/src/ViewControllers/ProfileViewController.m

@@ -5,6 +5,7 @@
 #import "ProfileViewController.h"
 #import "AppDelegate.h"
 #import "AvatarViewHelper.h"
+#import "OWSNavigationController.h"
 #import "OWSProfileManager.h"
 #import "Signal-Swift.h"
 #import "SignalsNavigationController.h"
@@ -27,7 +28,7 @@ typedef NS_ENUM(NSInteger, ProfileViewMode) {
 NSString *const kProfileView_Collection = @"kProfileView_Collection";
 NSString *const kProfileView_LastPresentedDate = @"kProfileView_LastPresentedDate";
 
-@interface ProfileViewController () <UITextFieldDelegate, AvatarViewHelperDelegate>
+@interface ProfileViewController () <UITextFieldDelegate, AvatarViewHelperDelegate, OWSNavigationView>
 
 @property (nonatomic, readonly) AvatarViewHelper *avatarViewHelper;
 
@@ -259,8 +260,6 @@ NSString *const kProfileView_LastPresentedDate = @"kProfileView_LastPresentedDat
     // context.
     switch (self.profileViewMode) {
         case ProfileViewMode_AppSettings:
-            self.navigationItem.leftBarButtonItem =
-                [self createOWSBackButtonWithTarget:self selector:@selector(backOrSkipButtonPressed)];
             break;
         case ProfileViewMode_UpgradeOrNag:
             self.navigationItem.leftBarButtonItem =
@@ -432,6 +431,7 @@ NSString *const kProfileView_LastPresentedDate = @"kProfileView_LastPresentedDat
 + (void)presentForAppSettings:(UINavigationController *)navigationController
 {
     OWSAssert(navigationController);
+    OWSAssert([navigationController isKindOfClass:[OWSNavigationController class]]);
 
     ProfileViewController *vc = [[ProfileViewController alloc] initWithMode:ProfileViewMode_AppSettings];
     [navigationController pushViewController:vc animated:YES];
@@ -440,6 +440,7 @@ NSString *const kProfileView_LastPresentedDate = @"kProfileView_LastPresentedDat
 + (void)presentForRegistration:(UINavigationController *)navigationController
 {
     OWSAssert(navigationController);
+    OWSAssert([navigationController isKindOfClass:[OWSNavigationController class]]);
 
     ProfileViewController *vc = [[ProfileViewController alloc] initWithMode:ProfileViewMode_Registration];
     [navigationController pushViewController:vc animated:YES];
@@ -450,7 +451,7 @@ NSString *const kProfileView_LastPresentedDate = @"kProfileView_LastPresentedDat
     OWSAssert(presentingController);
 
     ProfileViewController *vc = [[ProfileViewController alloc] initWithMode:ProfileViewMode_UpgradeOrNag];
-    UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:vc];
+    OWSNavigationController *navigationController = [[OWSNavigationController alloc] initWithRootViewController:vc];
     [presentingController presentTopLevelModalViewController:navigationController
                                             animateDismissal:YES
                                          animatePresentation:YES];
@@ -492,6 +493,13 @@ NSString *const kProfileView_LastPresentedDate = @"kProfileView_LastPresentedDat
     self.avatar = nil;
 }
 
+#pragma mark - OWSNavigationView
+
+- (void)navBackButtonPressed
+{
+    [self backOrSkipButtonPressed];
+}
+
 #pragma mark - Logging
 
 + (NSString *)tag

Signal/src/ViewControllers/SignalsNavigationController.h

@@ -2,8 +2,8 @@
 //  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
 //
 
-#import <UIKit/UIKit.h>
+#import "OWSNavigationController.h"
 
-@interface SignalsNavigationController : UINavigationController
+@interface SignalsNavigationController : OWSNavigationController
 
 @end

Signal/src/ViewControllers/SignalsViewController.m

@@ -10,6 +10,7 @@
 #import "MessagesViewController.h"
 #import "NSDate+millisecondTimeStamp.h"
 #import "OWSContactsManager.h"
+#import "OWSNavigationController.h"
 #import "ProfileViewController.h"
 #import "PropertyListPreferences.h"
 #import "PushManager.h"
@@ -309,7 +310,7 @@ typedef NS_ENUM(NSInteger, CellState) { kArchiveState, kInboxState };
 
 - (void)settingsButtonPressed:(id)sender {
     AppSettingsViewController *vc = [AppSettingsViewController new];
-    UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:vc];
+    OWSNavigationController *navigationController = [[OWSNavigationController alloc] initWithRootViewController:vc];
     [self presentViewController:navigationController animated:YES completion:nil];
 }
 
@@ -353,8 +354,8 @@ typedef NS_ENUM(NSInteger, CellState) { kArchiveState, kInboxState };
         //
         // We just want to make sure contact access is *complete* before showing the compose
         // screen to avoid flicker.
-        UINavigationController *navigationController =
+        OWSNavigationController *navigationController =
-            [[UINavigationController alloc] initWithRootViewController:viewController];
+            [[OWSNavigationController alloc] initWithRootViewController:viewController];
         [self presentTopLevelModalViewController:navigationController animateDismissal:YES animatePresentation:YES];
     }];
 }

Signal/src/ViewControllers/UpdateGroupViewController.m

@@ -10,6 +10,7 @@
 #import "ContactsViewHelper.h"
 #import "Environment.h"
 #import "OWSContactsManager.h"
+#import "OWSNavigationController.h"
 #import "OWSTableViewController.h"
 #import "Signal-Swift.h"
 #import "SignalKeyingStorage.h"
@@ -33,7 +34,8 @@ NS_ASSUME_NONNULL_BEGIN
     AvatarViewHelperDelegate,
     AddToGroupViewControllerDelegate,
     OWSTableViewControllerDelegate,
-    UINavigationControllerDelegate>
+    UINavigationControllerDelegate,
+    OWSNavigationView>
 
 @property (nonatomic, readonly) OWSMessageSender *messageSender;
 @property (nonatomic, readonly) ContactsViewHelper *contactsViewHelper;
@@ -103,8 +105,6 @@ NS_ASSUME_NONNULL_BEGIN
     self.previousMemberRecipientIds = [NSSet setWithArray:self.thread.groupModel.groupMemberIds];
 
     self.title = NSLocalizedString(@"EDIT_GROUP_DEFAULT_TITLE", @"The navbar title for the 'update group' view.");
-    self.navigationItem.leftBarButtonItem =
-        [self createOWSBackButtonWithTarget:self selector:@selector(backButtonPressed:)];
 
     // First section.
 
@@ -409,13 +409,13 @@ NS_ASSUME_NONNULL_BEGIN
 
 #pragma mark - Event Handling
 
-- (void)backButtonPressed:(id)sender
+- (void)backButtonPressed
 {
     [self.groupNameTextField resignFirstResponder];
 
     if (!self.hasUnsavedChanges) {
         // If user made no changes, return to conversation settings view.
-        [self dismissViewControllerAnimated:YES completion:nil];
+        [self.navigationController popViewControllerAnimated:YES];
         return;
     }
 
@@ -441,7 +441,7 @@ NS_ASSUME_NONNULL_BEGIN
                                                              @"The label for the 'don't save' button in action sheets.")
                                                    style:UIAlertActionStyleDestructive
                                                  handler:^(UIAlertAction *action) {
-                                                     [self dismissViewControllerAnimated:YES completion:nil];
+                                                     [self.navigationController popViewControllerAnimated:YES];
                                                  }]];
     [self presentViewController:controller animated:YES completion:nil];
 }
@@ -528,6 +528,13 @@ NS_ASSUME_NONNULL_BEGIN
     return [self.memberRecipientIds containsObject:recipientId];
 }
 
+#pragma mark - OWSNavigationView
+
+- (void)navBackButtonPressed
+{
+    [self backButtonPressed];
+}
+
 @end
 
 NS_ASSUME_NONNULL_END

Signal/src/util/UIViewController+OWS.h

@@ -17,8 +17,6 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (UIBarButtonItem *)createOWSBackButton;
 
-- (UIBarButtonItem *)createOWSBackButtonWithTarget:(id)target selector:(SEL)selector;
-
 @end
 
 NS_ASSUME_NONNULL_END