Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

iOS

Posted by Olivier Desmoulin
Olivier Desmoulin
5,258 Points

Problem detecting the end of a shake event when testing on my device

Hi Guys,

I tested the cristalball code on my device and sometimes, while shaking the device, the action of setting the predictionLabel to nil works well, but the action of setting it to a new value does not work. It's like if the following method is not called. - (void) motionEnded:(UIEventSubtype)motion withEvent:(UIEvent *)event{ if ( motion == UIEventSubtypeMotionShake ){ [self makePrediction]; }

Does that mean that some motion events that I could interpret as shake motions are not considered as shake motions by the device? How can I detect the ending of these motion events?

1 Answer

Amit Bijlani
STAFF
Amit Bijlani
Treehouse Guest Teacher
Amit Bijlani
Amit Bijlani
Treehouse Guest Teacher

There are two scenarios:

  1. Either it is assuming that you cancelled the shake event. In which case you should add a NSLog to the motionCancelled event.

  2. Or it is not registering as a shake event. In which case I would add NSLogs inside and outside the if statement if ( motion == UIEventSubtypeMotionShake ).

Olivier Desmoulin
Olivier Desmoulin
5,258 Points

Hi Amit,

thank you very much for your answer. Following your advices, I added the NSLogs inside the motionCancelled and inside and outside the if condition of the motionEnded event and actually, I noticed that my problem hapens when the device does not detect the end of the shaking event. After a short period of time, it considers it as a Cancelled motion. For this reason I added a call to the makePrediction method inside the motionCancelled event, so that each time I shake the device, it can make a prediction, even if it does not detect the end of the motion. Do you think this is an acceptable solution? Or do you have a better recommendation?

Amit Bijlani
Amit Bijlani
Treehouse Guest Teacher
Amit Bijlani
Amit Bijlani
Treehouse Guest Teacher

I don't think that is the right approach because you don't want a cancel event to fire a prediction. From what you wrote above it sounds like you might be shaking the device for too long and it finally registers it as cancelled.

Here's what Apple's documentation has to say:

An event is canceled if the shake motion is interrupted or if iOS determines that the motion is not valid after all—for example, if the shaking lasts too long.

Olivier Desmoulin
Olivier Desmoulin
5,258 Points

OK, Thank you Amit for your answer. best, Olivier