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I'm using UIImpactFeedbackGenerator as described in Apple's developer docs, but there seems to be a slight delay -- maybe a tenth of a second or similar -- between when I invoke impactOccurred and when you feel the haptic. This is especially evident when I am playing a sound at the same time - the sound clearly precedes the haptic.

Someone else wrote about the same thing in Apple Developer Forums, but no resolution.

I initialize the UIImpactFeedbackGenerator with:

// Set up impact
UIImpactFeedbackStyle sty = UIImpactFeedbackStyleMedium;
impactFeedbackGen = [[UIImpactFeedbackGenerator alloc] initWithStyle:sty];

Immediately call prepare, and call repeatedly during the few seconds that pass before the impact occurs:

[impactFeedbackGen prepare];

Then finally play the haptic, with:

[impactFeedbackGen impactOccurred];

Not sure if it's related, but I am using UISelectionFeedbackGenerator in the same app, but not at the same time.

Thoughts? Thanks!

drewster
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1 Answers1

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I think the trick with avoiding delay with UIImpactFeedbackGenerator is when to call prepare.

Obviously you can't simply call prepare and then immediate trigger the impact, since the engine needs time to actually prepare.

On the other hand, once prepare is called, the taptic engine will only stay in a prepared state for a short duration (a matter of seconds), in order to conserve power.

It is possible to extend the prepared state by calling prepare multiple times, however you have to be careful here as well, since after a certain threshold, the system will put the engine back to an idle state, and ignore further calls to prepare until after an impact is triggered.

Allan Poole
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  • Right, I read the documentation also -- I'm going it in advance by about 2 seconds or so typically.. have also tried shorter and longer timeframes, but there is always a delay. – drewster May 17 '17 at 20:00