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fix(iOS): restore native behavior of auto shortening back button title #2105

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merged 3 commits into from
Apr 29, 2024
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fix(iOS): restore native behavior of auto shortening back button title #2105

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fix(iOS): restore native behavior of auto shortening back button title
zetavg Apr 14, 2024
07c7e1e
chore: add comment to explain why comparing backTitleFontFamily again…
zetavg Apr 17, 2024
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zetavg Apr 18, 2024
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21 changes: 19 additions & 2 deletions ios/RNSScreenStackHeaderConfig.mm
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Original file line number Diff line number Diff line change
Expand Up @@ -511,8 +511,17 @@ + (void)updateViewController:(UIViewController *)vc
action:nil];
[backBarButtonItem setMenuHidden:config.disableBackButtonMenu];

auto isBackButtonCustomized = !isBackTitleBlank || config.disableBackButtonMenu || NO;
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if (config.isBackTitleVisible) {
if (config.backTitleFontFamily || config.backTitleFontSize) {
if ((config.backTitleFontFamily &&
// While being used by react-navigation, the `backTitleFontFamily` will
// be set to "System" by default - which is the system default font.
// To avoid always considering the font as customized, we need to have an additional check.
// See: https://github.com/software-mansion/react-native-screens/pull/2105#discussion_r1565222738
![config.backTitleFontFamily isEqual:@"System"]) ||
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Why do we need to check the font family here?

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It's because due to the current implementation of @react-navigation/native-stack, backTitleFontFamily will always be assigned to the font family of fonts.regular, which will be "System" if the default theme is used.

It seems that the "System" font family is already the default on iOS, as setting the font family to "System" does not change the appearance, but in this case, will make config.backTitleFontFamily always resolve to YES.

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I see. Do you know, if we could rely on the native component that represents the title of back button, instead of comparing config.backTitleFontFamily?

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@kkafar kkafar Apr 15, 2024 •
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Thanks for the PR, this is great!

Can we have this comment in the code please? @zetavg

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@zetavg zetavg Apr 15, 2024 •
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Thanks for the comment @tboba, but I'm sorry that due to my limited knowledge, I can't quite understand what you mean. Do you suggest we can handle this in something like the getter/setter of RNSScreenStackHeaderConfig, or the JS code in react-navigation?

@kkafar Sure, I'll add comments to explain this besides related code once we finalize the solution.

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@tboba tboba Apr 16, 2024 •
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@zetavg I'm wondering if it would be possible to get title component of back title and check if it has default font set, but after further reflections I'm afraid this could lead to some flickers (setting the font and other properties -> checking the font of the native component -> setting system back 😄), so I guess we can stay with the current solution.

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Thanks for explaining, I think I got your point! I do think the current solution of comparing the font against "System" isn't perfect, one way is that there may be different ways to use the same system font (maybe ".AppleSystemUIFont"? I'm not sure), and if react-navigation changes to also assign a default value to config.backTitleFontSize this will break again.

Your solution inspired me to think of a possible way to get this native behavior to work while still customizing the back button (such as changing the font or customizing the shortened "Back" text) - measure the width of the headerTitle and headerRight to see if there's enough space on layout, and replace the backButtonTitle with the shortened text or hide it. Well, flickering may be a problem.

config.backTitleFontSize) {
isBackButtonCustomized = YES;
NSMutableDictionary *attrs = [NSMutableDictionary new];
NSNumber *size = config.backTitleFontSize ?: @17;
if (config.backTitleFontFamily) {
Expand All @@ -535,9 +544,17 @@ + (void)updateViewController:(UIViewController *)vc
// When backBarButtonItem's title is null, back menu will use value
// of backButtonTitle
[backBarButtonItem setTitle:nil];
isBackButtonCustomized = YES;
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Hi @zetavg, I know that this PR is already merged, but I wonder why do you set isBackButtonCustomized to true here. My understanding is that this else block is for the case when we hide back button, but want to preserve it in back menu. So, by default when we have navigationItem hidden we don't display anything here - nothing is customized, when we want to custom hide it from back manu then we set config.disableBackButtonMenu which is in initial condition anyway.

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Quick reply - I think it's because this isBackButtonCustomized is used to determine whether we need to assign the backBarButtonItem to prevItem.backBarButtonItem later on line 556.

Since backBarButtonItem has been changed here ([backBarButtonItem setTitle:nil];), my understanding is that the changed backBarButtonItem has to be assigned to prevItem.backBarButtonItem for the changes to take effect. So it should be considered customized - or changed. Maybe it's better to rename isBackButtonCustomized to isBackBarButtonItemChanged so that it will be more clear (or use another way to track if we have changed anything on backBarButtonItem).

My guess is that if we do not set isBackButtonCustomized to true here, the back title won't be hidden as expected. I may need to verify it though.

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Maybe it's better to rename isBackButtonCustomized to isBackBarButtonItemChanged ...

Oh, I see that you had already done this in #2123. 🎉

prevItem.backButtonTitle = resolvedBackTitle;
}
prevItem.backBarButtonItem = backBarButtonItem;

// Prevent unnecessary assignment of backBarButtonItem if it is not customized,
// as assigning one will override the native behavior of automatically shortening
// the title to "Back" or hide the back title if there's not enough space.
// See: https://github.com/software-mansion/react-native-screens/issues/1589
if (isBackButtonCustomized) {
prevItem.backBarButtonItem = backBarButtonItem;
}

if (@available(iOS 11.0, *)) {
if (config.largeTitle) {
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