CODEWITHSUNDEEP
iphoneobjective-cuiscrollview
prostock
prostock

Reputation: 9535

UIScrollView touch handling

I'm reading the following about UIScrollView from Apple UIScrollView Class Reference Documentation:

Because a scroll view has no scroll bars, it must know whether a touch signals an intent to scroll versus an intent to track a subview in the content. To make this determination, it temporarily intercepts a touch-down event by starting a timer and, before the timer fires, seeing if the touching finger makes any movement. If the timer fires without a significant change in position, the scroll view sends tracking events to the touched subview of the content view. If the user then drags their finger far enough before the timer elapses, the scroll view cancels any tracking in the subview and performs the scrolling itself. Subclasses can override the touchesShouldBegin:withEvent:inContentView:, pagingEnabled, and touchesShouldCancelInContentView: methods (which are called by the scroll view) to affect how the scroll view handles scrolling gestures.

I don't understand the sentence starting with "If the user then drags their finger far enough before the timer elapses..." I thought the timer already fired according to the previous sentence. Is it talking about another timer in this one?

Upvotes: 0

Views: 1061

Answers (1)

nielsbot
nielsbot

Reputation: 16022

It's confusing. I believe there are 2 possible behaviors depending on whether your scrollView has the delaysContentTouches property set (and or the canCancelContentTouches property is set)

If delaysContentTouches is set:

When the user taps the scroll view it temporarily intercepts a touch-down event by starting a timer and, before the timer fires, seeing if the touching finger makes any movement. If the timer fires without a significant change in position, the scroll view sends tracking events to the touched subview of the content view. If the user drags their finger far enough before the timer elapses, the scroll view begins scrolling.

If the timer has fired:

If canCancelContentTouches is set the scroll view cancels and touches passed to its subviews and begins scrolling. Otherwise, no scrolling.

If timer has not expired before the user drags his/her finger, scrolling happens.

I think I got that right... (someone might want to double-check)

HTH

Upvotes: 2

Related Questions