feat(ios): optional tradeoff to fix ios input delay

[andreasgangso]

Connection with issue(s)

Resolves issue #1268

Possibly connected to #216

Testing and Review Notes

Description
There's a very noticable input delay on iOS which is not usable if you want websites with a lot of gestures (e.g. games or similar). To test, simply have a website with a button and see how long it takes to click it before and after enabling the new preventGestureDelay flag.

Cause
I understand this is somehow caused by flutter's DelayingGestureRecognizer.

I honestly don't understand what makes the "WaitUntilTouchesEnded" policy work better here, but it removes the delay.
Other solutions include disabling the DelayingGestureRecognizer completely, but that's very hacky compared to using an official option.

I see google maps is using this policy, so it can't be too bad?
https://github.com/flutter/packages/blob/d449a17f8706850388a16d8acc72398c2118cf9a/packages/google_maps_flutter/google_maps_flutter_ios/ios/Classes/FLTGoogleMapsPlugin.m#L16

Tradeoffs
I put this behind the optional flag preventGestureDelay because this has 1 known tradeoff.
This makes the gestures to always fall through to the webview, even if there are opaque widgets stacked on top of it (see
flutter/flutter#94325 (comment))

To Do

• double check the original issue to confirm it is fully satisfied
• add testing notes and screenshots in PR description to help guide reviewers

[andreasgangso]

Any opinions on this @pichillilorenzo?
What are the chances of this being merged?

[harryhjsh]

Any chance of this getting merged?

[andreasgangso]

Any update @pichillilorenzo?
I'd be happy to do edits if you got any comments.

[andreasgangso]

@pichillilorenzo let me know if anything needs to be done here

[pichillilorenzo]

@andreasgangso I was trying this fix but currently, I don't see any delay improvements in using FlutterPlatformViewGestureRecognizersBlockingPolicyWaitUntilTouchesEnded.
For example, if you double-tap quickly on a button, it still counts as just one tap.

Instead, adding this code inside hitTest override method of InAppWebView.swift:

public override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
  // other code ...

      if let gestures = superview?.superview?.gestureRecognizers {
          for gesture in gestures {
              if NSStringFromClass(type(of: gesture)) == "DelayingGestureRecognizer" {
                  gesture.isEnabled = false
              }
          }
      }
  // other code ...
}

it seems to work.

I can update this code to work with preventGestureDelay property and call that piece of code only if it is true

[pichillilorenzo]

About the tradeoffs, it seems to work correctly also with flutter widgets that are over the webview, such as ElevatedButton.
The flutter button tap event seems to not fall through the webview.

I'm using Flutter 3.13.8

[pichillilorenzo]

@all-contributors please add @andreasgangso for code

[allcontributors]

@pichillilorenzo

I've put up a pull request to add @andreasgangso! 🎉

[codemobiles]

I still see the delay problem. Have the problem been really fixed in v6.0.0-beta.28? Thanks

[andreasgangso]

I still see the delay problem. Have the problem been really fixed in v6.0.0-beta.28? Thanks

Are you using the preventGestureDelay flag?

[pichillilorenzo]

@codemobiles using the InAppWebView.preventGestureDelay parameter. It should disable the Flutter native delay gesture.

[codemobiles]

Thanks so much. I forgot to set preventGestureDelay first. ex: InAppWebView(...preventGestureDelay: true,); It fixed the problem. @andreasgangso @pichillilorenzo

[tangsj]

On version 6.1.5, the preventGestureDelay parameter seems to have no effect.

[andreasgangso]

On version 6.1.5, the preventGestureDelay parameter seems to have no effect.

Any reason you're not using webview_flutter? I migrated to it a year ago. It's actively maintained and has a lot of features now. Don't think i had this problem with that one.