Help with timers

[Anonymous Username]

I want a timer to only work when I hold down the button, and stop counting when you let go. Im using two IBActions one touch up inside and one touch down. The touch up invalidates the timer and the touch down starts one, is there a better way?

[Duncan C]

Originally Posted by Anonymous Username

I want a timer to only work when I hold down the button, and stop counting when you let go. Im using two IBActions one touch up inside and one touch down. The touch up invalidates the timer and the touch down starts one, is there a better way?

It depends on your needs. If you need the timer to start exactly at the moment the user presses down, then yes, creating a timer on touch down is the way to go.

If you can tolerate a little slop, you could have a repeating timer running all the time, with the code the timer calls turned on and off by a BOOL instance variable. Let's call it timerActive.

On touch down, you'd set timerActive to true. On touchUp, you'd set timerActive to false.

The code that decrements your counter and displays the result would be inside an if statement: ("If (timerActive) {decrement counter and display}")

That approach would cause the first interval to be short sometimes, since the timer will already be "in flight" when the user presses the button.

I'd say since you've already done the work to create a new timer on touch down, and kill it on touch up, keep that approach. It's more accurate, but a little more work to set up. The work is done, so why do more work to implement a less accurate method? Just make sure your logic will never try to invalidate an already invalidated timer. That will cause a crash. I'd suggest setting your timer's instance variable to nil when you invalidate it.

[Anonymous Username]

Thank You! I feel weird having three IBActions (the third one invalidates the timer if you leave the button) I was just making sure this is the best way to do this.

[Duncan C]

Originally Posted by Anonymous Username

Thank You! I feel weird having three IBActions (the third one invalidates the timer if you leave the button) I was just making sure this is the best way to do this.

You could probably tie the touch up outside event to the same action as the touch up inside (stopping the timer.) So you have 3 events, but only 2 actions.

[Anonymous Username]

I never knew you could do that! Thank you!

[Duncan C]

Originally Posted by Anonymous Username

I never knew you could do that! Thank you!

Absolutely. It's a very useful technique.

Say you're writing a quiz app, and the user has to pick button a, button b, button c, or button d for each question.

You can use a single IBAction for all the buttons, and put a different tag number on each one. The code IBAction can use the tag property of each button to figure out what button was pressed, and index into an array of questions to see if that button was the correct answer for the current question.

You can also set the target and selector on multiple gesture recognizers to the same method in much the same way, and use the tag of the view the gesture recognizer is linked to to figure out what to do.