From f7c81bae9d44aeb448200bfe403ee47738d7ff6a Mon Sep 17 00:00:00 2001
From: Matthew Chen <charlesmchen@gmail.com>
Date: Thu, 22 Jun 2017 10:55:26 -0400
Subject: [PATCH] =?UTF-8?q?Show=20the=20=E2=80=9Cscroll=20down=E2=80=9D=20?=
 =?UTF-8?q?button=20if=20user=20scrolls=20up,=20even=20if=20there=20are=20?=
 =?UTF-8?q?no=20unread=20messages.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

// FREEBIE
---
 .../ConversationView/MessagesViewController.m  | 18 ++++++++++++++++--
 .../OWSMessagesComposerTextView.h              |  2 +-
 .../OWSMessagesComposerTextView.m              |  6 +++---
 3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/Signal/src/ViewControllers/ConversationView/MessagesViewController.m b/Signal/src/ViewControllers/ConversationView/MessagesViewController.m
index cfcb01673..464747b0e 100644
--- a/Signal/src/ViewControllers/ConversationView/MessagesViewController.m
+++ b/Signal/src/ViewControllers/ConversationView/MessagesViewController.m
@@ -2793,6 +2793,7 @@ typedef enum : NSUInteger {
     [super viewDidLayoutSubviews];
 
     [self updateLastVisibleTimestamp];
+    [self ensureScrollDownButton];
 }
 
 - (void)createScrollDownButton
@@ -2838,6 +2839,14 @@ typedef enum : NSUInteger {
 
     BOOL shouldShowScrollDownButton = NO;
     NSUInteger numberOfMessages = [self.messageMappings numberOfItemsInSection:0];
+    CGFloat scrollSpaceToBottom = (self.collectionView.contentSize.height + self.collectionView.contentInset.bottom
+        - (self.collectionView.contentOffset.y + self.collectionView.frame.size.height));
+    CGFloat pageHeight = (self.collectionView.frame.size.height
+        - (self.collectionView.contentInset.top + self.collectionView.contentInset.bottom));
+    // Show "scroll down" button if user is scrolled up at least
+    // one page.
+    BOOL isScrolledUp = scrollSpaceToBottom > pageHeight * 1.f;
+
     if (numberOfMessages > 0) {
         TSInteraction *lastInteraction =
             [self interactionAtIndexPath:[NSIndexPath indexPathForRow:(NSInteger)numberOfMessages - 1 inSection:0]];
@@ -2845,6 +2854,8 @@ typedef enum : NSUInteger {
 
         if (lastInteraction.timestampForSorting > self.lastVisibleTimestamp) {
             shouldShowScrollDownButton = YES;
+        } else if (isScrolledUp) {
+            shouldShowScrollDownButton = YES;
         }
     }
 
@@ -3992,7 +4003,7 @@ typedef enum : NSUInteger {
     [self presentViewController:controller animated:YES completion:nil];
 }
 
-- (void)textViewDidChangePosition
+- (void)textViewDidChangeLayout
 {
     OWSAssert([NSThread isMainThread]);
 
@@ -4006,6 +4017,8 @@ typedef enum : NSUInteger {
                                                                    userInfo:nil
                                                                     repeats:NO];
     }
+
+    [self ensureScrollDownButton];
 }
 
 - (void)scrollToBottomImmediately
@@ -4096,6 +4109,8 @@ typedef enum : NSUInteger {
     // We want to show the "voice message" button if the text input is empty
     // and the "send" button if it isn't.
     [((OWSMessagesToolbarContentView *)self.inputToolbar.contentView)ensureEnabling];
+
+    [self ensureScrollDownButton];
 }
 
 #pragma mark - UIScrollViewDelegate
@@ -4162,7 +4177,6 @@ typedef enum : NSUInteger {
 
 #pragma mark - OWSMessagesCollectionViewFlowLayoutDelegate
 
-
 - (BOOL)shouldShowCellDecorationsAtIndexPath:(NSIndexPath *)indexPath
 {
     TSInteraction *interaction = [self interactionAtIndexPath:indexPath];
diff --git a/Signal/src/ViewControllers/ConversationView/OWSMessagesComposerTextView.h b/Signal/src/ViewControllers/ConversationView/OWSMessagesComposerTextView.h
index e25b6dbc5..8a2ef7f3a 100644
--- a/Signal/src/ViewControllers/ConversationView/OWSMessagesComposerTextView.h
+++ b/Signal/src/ViewControllers/ConversationView/OWSMessagesComposerTextView.h
@@ -12,7 +12,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (void)didPasteAttachment:(SignalAttachment *_Nullable)attachment;
 
-- (void)textViewDidChangePosition;
+- (void)textViewDidChangeLayout;
 
 @end
 
diff --git a/Signal/src/ViewControllers/ConversationView/OWSMessagesComposerTextView.m b/Signal/src/ViewControllers/ConversationView/OWSMessagesComposerTextView.m
index 077ce03f8..d0d245636 100644
--- a/Signal/src/ViewControllers/ConversationView/OWSMessagesComposerTextView.m
+++ b/Signal/src/ViewControllers/ConversationView/OWSMessagesComposerTextView.m
@@ -19,7 +19,7 @@ NS_ASSUME_NONNULL_BEGIN
     BOOL becameFirstResponder = [super becomeFirstResponder];
     if (becameFirstResponder) {
         // Intercept to scroll to bottom when text view is tapped.
-        [self.textViewPasteDelegate textViewDidChangePosition];
+        [self.textViewPasteDelegate textViewDidChangeLayout];
     }
     return becameFirstResponder;
 }
@@ -61,7 +61,7 @@ NS_ASSUME_NONNULL_BEGIN
     [super setFrame:frame];
 
     if (didChangeSize && isNonEmpty) {
-        [self.textViewPasteDelegate textViewDidChangePosition];
+        [self.textViewPasteDelegate textViewDidChangeLayout];
     }
 }
 
@@ -73,7 +73,7 @@ NS_ASSUME_NONNULL_BEGIN
     [super setBounds:bounds];
 
     if (didChangeSize && isNonEmpty) {
-        [self.textViewPasteDelegate textViewDidChangePosition];
+        [self.textViewPasteDelegate textViewDidChangeLayout];
     }
 }