Rework "cancel navigate back" logic.

// FREEBIE

Signal/src/ViewControllers/ConversationView/MessagesViewController.m

@@ -158,7 +158,6 @@ typedef enum : NSUInteger {
     OWSVoiceMemoGestureDelegate,
     UIDocumentMenuDelegate,
     UIDocumentPickerDelegate,
-    UIGestureRecognizerDelegate,
     UIImagePickerControllerDelegate,
     UINavigationControllerDelegate,
     UITextViewDelegate>
@@ -549,10 +548,6 @@ typedef enum : NSUInteger {
     // In case we're dismissing a CNContactViewController which requires default system appearance
     [UIUtil applySignalAppearence];
 
-    // Since we're using a custom back button, we have to do some extra work to manage the
-    // interactivePopGestureRecognizer
-    self.navigationController.interactivePopGestureRecognizer.delegate = self;
-
     // We need to recheck on every appearance, since the user may have left the group in the settings VC,
     // or on another device.
     [self hideInputIfNeeded];
@@ -992,10 +987,6 @@ typedef enum : NSUInteger {
 
     self.isViewVisible = NO;
 
-    // Since we're using a custom back button, we have to do some extra work to manage the
-    // interactivePopGestureRecognizer
-    self.navigationController.interactivePopGestureRecognizer.delegate = nil;
-
     [self.audioAttachmentPlayer stop];
     self.audioAttachmentPlayer = nil;
 

Signal/src/ViewControllers/NewGroupViewController.m

@@ -50,6 +50,7 @@ const NSUInteger kNewGroupViewControllerAvatarWidth = 68;
 @property (nonatomic) NSMutableSet<NSString *> *memberRecipientIds;
 
 @property (nonatomic) BOOL hasUnsavedChanges;
+@property (nonatomic) BOOL shouldIgnoreSavedChanges;
 @property (nonatomic) BOOL hasAppeared;
 
 @end
@@ -551,7 +552,7 @@ const NSUInteger kNewGroupViewControllerAvatarWidth = 68;
 {
     [self.groupNameTextField resignFirstResponder];
 
-    if (!self.hasUnsavedChanges) {
+    if (!self.hasUnsavedChanges || self.shouldIgnoreSavedChanges) {
         // If user made no changes, return to conversation settings view.
         [self.navigationController popViewControllerAnimated:YES];
         return;
@@ -570,6 +571,7 @@ const NSUInteger kNewGroupViewControllerAvatarWidth = 68;
                                                      @"The label for the 'discard' button in alerts and action sheets.")
                                            style:UIAlertActionStyleDestructive
                                          handler:^(UIAlertAction *action) {
+                                             self.shouldIgnoreSavedChanges = YES;
                                              [self.navigationController popViewControllerAnimated:YES];
                                          }]];
     [controller addAction:[UIAlertAction actionWithTitle:NSLocalizedString(@"TXT_CANCEL_TITLE", nil)
@@ -651,9 +653,13 @@ const NSUInteger kNewGroupViewControllerAvatarWidth = 68;
 
 #pragma mark - OWSNavigationView
 
-- (void)navBackButtonPressed
+- (BOOL)shouldCancelNavigationBack
 {
-    [self backButtonPressed];
+    BOOL result = self.hasUnsavedChanges && !self.shouldIgnoreSavedChanges;
+    if (result) {
+        [self backButtonPressed];
+    }
+    return result;
 }
 
 @end

Signal/src/ViewControllers/OWSNavigationController.h

@@ -4,9 +4,11 @@
 
 #import <UIKit/UIKit.h>
 
+// Any view controller which wants to be able cancel back button
+// presses and back gestures should implement this protocol.
 @protocol OWSNavigationView <NSObject>
 
-- (void)navBackButtonPressed;
+- (BOOL)shouldCancelNavigationBack;
 
 @end
 

Signal/src/ViewControllers/OWSNavigationController.m

@@ -4,7 +4,15 @@
 
 #import "OWSNavigationController.h"
 
-@interface OWSNavigationController ()
+// We use a category to expose UINavigationController's private
+// UINavigationBarDelegate methods.
+@interface UINavigationController (OWSNavigationController) <UINavigationBarDelegate>
+
+@end
+
+#pragma mark -
+
+@interface OWSNavigationController () <UIGestureRecognizerDelegate>
 
 @end
 
@@ -12,24 +20,53 @@
 
 @implementation OWSNavigationController
 
-- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item
+- (void)viewDidLoad
 {
+    [super viewDidLoad];
 
+    self.interactivePopGestureRecognizer.delegate = self;
+}
+
+#pragma mark - UINavigationBarDelegate
+
+// All UINavigationController serve as the UINavigationBarDelegate for their navbar.
+// We override shouldPopItem: in order to cancel some back button presses - for example,
+// if a view has unsaved changes.
+- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item
+{
+    OWSAssert(self.interactivePopGestureRecognizer.delegate == self);
     UIViewController *topViewController = self.topViewController;
-    BOOL wasBackButtonClicked = topViewController.navigationItem == item;
 
+    BOOL wasBackButtonClicked = topViewController.navigationItem == item;
+    BOOL result = YES;
     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;
+        if ([topViewController conformsToProtocol:@protocol(OWSNavigationView)]) {
+            id<OWSNavigationView> navigationView = (id<OWSNavigationView>)topViewController;
+            result = ![navigationView shouldCancelNavigationBack];
         }
+    }
+
+    // If we're not going to cancel the pop/back, we need to call the super
+    // implementation since it has important side effects.
+    if (result) {
+        result = [super navigationBar:navigationBar shouldPopItem:item];
+        OWSAssert(result);
+    }
+    return result;
+}
+
+#pragma mark - UIGestureRecognizerDelegate
+
+// We serve as the UIGestureRecognizerDelegate of the interactivePopGestureRecognizer
+// in order to cancel some "back" gestures - for example,
+// if a view has unsaved changes.
+- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer
+{
+    UIViewController *topViewController = self.topViewController;
+    if ([topViewController conformsToProtocol:@protocol(OWSNavigationView)]) {
+        id<OWSNavigationView> navigationView = (id<OWSNavigationView>)topViewController;
+        return ![navigationView shouldCancelNavigationBack];
     } else {
-        // when you call popViewController programmatically you do not want to pop it twice
         return YES;
     }
 }

Signal/src/ViewControllers/ProfileViewController.m

@@ -44,6 +44,8 @@ NSString *const kProfileView_LastPresentedDate = @"kProfileView_LastPresentedDat
 
 @property (nonatomic) BOOL hasUnsavedChanges;
 
+@property (nonatomic) BOOL shouldIgnoreSavedChanges;
+
 @property (nonatomic) ProfileViewMode profileViewMode;
 
 @property (nonatomic) YapDatabaseConnection *databaseConnection;
@@ -207,7 +209,7 @@ NSString *const kProfileView_LastPresentedDate = @"kProfileView_LastPresentedDat
 {
     [self.nameTextField resignFirstResponder];
 
-    if (!self.hasUnsavedChanges) {
+    if (!self.hasUnsavedChanges || self.shouldIgnoreSavedChanges) {
         // If user made no changes, return to conversation settings view.
         [self profileCompletedOrSkipped];
         return;
@@ -226,6 +228,7 @@ NSString *const kProfileView_LastPresentedDate = @"kProfileView_LastPresentedDat
                                                      @"The label for the 'discard' button in alerts and action sheets.")
                                            style:UIAlertActionStyleDestructive
                                          handler:^(UIAlertAction *action) {
+                                             self.shouldIgnoreSavedChanges = YES;
                                              [self profileCompletedOrSkipped];
                                          }]];
     [controller addAction:[UIAlertAction actionWithTitle:NSLocalizedString(@"TXT_CANCEL_TITLE", nil)
@@ -495,9 +498,13 @@ NSString *const kProfileView_LastPresentedDate = @"kProfileView_LastPresentedDat
 
 #pragma mark - OWSNavigationView
 
-- (void)navBackButtonPressed
+- (BOOL)shouldCancelNavigationBack
 {
-    [self backOrSkipButtonPressed];
+    BOOL result = self.hasUnsavedChanges && !self.shouldIgnoreSavedChanges;
+    if (result) {
+        [self backOrSkipButtonPressed];
+    }
+    return result;
 }
 
 #pragma mark - Logging

Signal/src/ViewControllers/UpdateGroupViewController.m

@@ -50,6 +50,7 @@ NS_ASSUME_NONNULL_BEGIN
 @property (nonatomic) NSMutableSet<NSString *> *memberRecipientIds;
 
 @property (nonatomic) BOOL hasUnsavedChanges;
+@property (nonatomic) BOOL shouldIgnoreSavedChanges;
 
 @end
 
@@ -413,7 +414,7 @@ NS_ASSUME_NONNULL_BEGIN
 {
     [self.groupNameTextField resignFirstResponder];
 
-    if (!self.hasUnsavedChanges) {
+    if (!self.hasUnsavedChanges || self.shouldIgnoreSavedChanges) {
         // If user made no changes, return to conversation settings view.
         [self.navigationController popViewControllerAnimated:YES];
         return;
@@ -441,6 +442,7 @@ NS_ASSUME_NONNULL_BEGIN
                                                              @"The label for the 'don't save' button in action sheets.")
                                                    style:UIAlertActionStyleDestructive
                                                  handler:^(UIAlertAction *action) {
+                                                     self.shouldIgnoreSavedChanges = YES;
                                                      [self.navigationController popViewControllerAnimated:YES];
                                                  }]];
     [self presentViewController:controller animated:YES completion:nil];
@@ -530,9 +532,13 @@ NS_ASSUME_NONNULL_BEGIN
 
 #pragma mark - OWSNavigationView
 
-- (void)navBackButtonPressed
+- (BOOL)shouldCancelNavigationBack
 {
-    [self backButtonPressed];
+    BOOL result = self.hasUnsavedChanges && !self.shouldIgnoreSavedChanges;
+    if (result) {
+        [self backButtonPressed];
+    }
+    return result;
 }
 
 @end