[UIScrollViewDelegate]简介

The methods declared by the UIScrollViewDelegate protocol allow the adopting delegate to respond to messages from the UIScrollView class and thus respond to, and in some affect, operations such as scrolling, zooming, deceleration of scrolled content, and scrolling animations.

通过UIScrollViewDelegate协议声明的方法允许采用的代表来响应来自UIScrollView类的信息，因此在某些情况下，响应像滚动，缩放，滚动内容的减速和滚动的动画等操作。

Responding to Scrolling and Dragging

• scrollViewDidScroll:

  Tells the delegate when the user scrolls the content view within the receiver.

  当用户滚动接收器内的内容视图时通知delegate。

  Declaration

  SWIFT

  optional func scrollViewDidScroll(_ scrollView: UIScrollView)

  OBJECTIVE-C

  - (void)scrollViewDidScroll:(UIScrollView *)scrollView


  Parameters

  scrollView

  The scroll-view object in which the scrolling occurred. 滚动发生的滚动视图对象。

  Discussion

  The delegate typically implements this method to obtain the change in content offset from scrollView and draw the affected portion of the content view. 

  delegate典型实现这个方法从scrollView获取内容边际的变化和现实内容视图受影响的部分。

  Import Statement

  import UIKit

  Availability

  Available in iOS 2.0 and later.

  See Also

  – scrollViewWillBeginDragging:
– scrollViewDidEndDragging:willDecelerate:

• scrollViewWillBeginDragging:

  Tells the delegate when the scroll view is about to start scrolling the content.

  Declaration

  SWIFT

  optional func scrollViewWillBeginDragging(_ scrollView: UIScrollView)

  OBJECTIVE-C

  - (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView


  Parameters

  scrollView

  The scroll-view object that is about to scroll the content view.

  Discussion

  The delegate might not receive this message until dragging has occurred over a small distance.

  Import Statement

  import UIKit

  Availability

  Available in iOS 2.0 and later.

  See Also

  – scrollViewDidScroll:
– scrollViewDidEndDragging:willDecelerate:

• scrollViewWillEndDragging:withVelocity:targetContentOffset:

  Tells the delegate when the user finishes scrolling the content.

  Declaration

  SWIFT

  optional func scrollViewWillEndDragging(_ scrollView: UIScrollView,
                           withVelocity velocity: CGPoint,
                    targetContentOffset targetContentOffset: UnsafeMutablePointer<CGPoint>)

  OBJECTIVE-C

  - (void)scrollViewWillEndDragging:(UIScrollView *)scrollView
                     withVelocity:(CGPoint)velocity
              targetContentOffset:(inout CGPoint *)targetContentOffset


  Parameters

  scrollView	The scroll-view object where the user ended the touch..
  velocity	The velocity of the scroll view (in points) at the moment the touch was released.
  targetContentOffset	The expected offset when the scrolling action decelerates to a stop.

  Discussion

  This method is not called when the value of the scroll view’s pagingEnabled property is YES. Your application can change the value of the targetContentOffset parameter to adjust where the scrollview finishes its scrolling animation.

  Import Statement

  import UIKit

  Availability

  Available in iOS 5.0 and later.

• scrollViewDidEndDragging:willDecelerate:

  Tells the delegate when dragging ended in the scroll view.

  Declaration

  SWIFT

  optional func scrollViewDidEndDragging(_ scrollView: UIScrollView,
                        willDecelerate decelerate: Bool)

  OBJECTIVE-C

  - (void)scrollViewDidEndDragging:(UIScrollView *)scrollView
                  willDecelerate:(BOOL)decelerate


  Parameters

  scrollView	The scroll-view object that finished scrolling the content view.
  decelerate	YES if the scrolling movement will continue, but decelerate, after a touch-up gesture during a dragging operation. If the value is NO, scrolling stops immediately upon touch-up.

  Discussion

  The scroll view sends this message when the user’s finger touches up after dragging content. The decelerating property of UIScrollView controls deceleration.

  Import Statement

  import UIKit

  Availability

  Available in iOS 2.0 and later.

  See Also

  – scrollViewDidScroll:
– scrollViewWillBeginDragging:
– scrollViewWillBeginDecelerating:

• scrollViewShouldScrollToTop:

  Asks the delegate if the scroll view should scroll to the top of the content.

  Declaration

  SWIFT

  optional func scrollViewShouldScrollToTop(_ scrollView: UIScrollView) -> Bool

  OBJECTIVE-C

  - (BOOL)scrollViewShouldScrollToTop:(UIScrollView *)scrollView


  Parameters

  scrollView

  The scroll-view object requesting this information.

  Return Value

  YES to permit scrolling to the top of the content, NO to disallow it.

  Discussion

  If the delegate doesn’t implement this method, YES is assumed. For the scroll-to-top gesture (a tap on the status bar) to be effective, the scrollsToTop property of the UIScrollView must be set to YES. 

  Import Statement

  import UIKit

  Availability

  Available in iOS 2.0 and later.

  See Also

  – scrollViewDidScrollToTop:
– scrollViewDidScroll:

• scrollViewDidScrollToTop:

  Tells the delegate that the scroll view scrolled to the top of the content.

  Declaration

  SWIFT

  optional func scrollViewDidScrollToTop(_ scrollView: UIScrollView)

  OBJECTIVE-C

  - (void)scrollViewDidScrollToTop:(UIScrollView *)scrollView


  Parameters

  scrollView

  The scroll-view object that perform the scrolling operation.

  Discussion

  The scroll view sends this message when it finishes scrolling to the top of the content. It might call it immediately if the top of the content is already shown. For the scroll-to-top gesture (a tap on the status bar) to be effective, the scrollsToTop property of the UIScrollView must be set to YES.

  Import Statement

  import UIKit

  Availability

  Available in iOS 2.0 and later.

  See Also

  – scrollViewShouldScrollToTop:
– scrollViewDidScroll:

• scrollViewWillBeginDecelerating:

  Tells the delegate that the scroll view is starting to decelerate the scrolling movement.

  Declaration

  SWIFT

  optional func scrollViewWillBeginDecelerating(_ scrollView: UIScrollView)

  OBJECTIVE-C

  - (void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView


  Parameters

  scrollView

  The scroll-view object that is decelerating the scrolling of the content view.

  Discussion

  The scroll view calls this method as the user’s finger touches up as it is moving during a scrolling operation; the scroll view will continue to move a short distance afterwards. The decelerating property of UIScrollView controls deceleration.

  Import Statement

  import UIKit

  Availability

  Available in iOS 2.0 and later.

  See Also

  – scrollViewDidEndDecelerating:

• scrollViewDidEndDecelerating:

  Tells the delegate that the scroll view has ended decelerating the scrolling movement.

  Declaration

  SWIFT

  optional func scrollViewDidEndDecelerating(_ scrollView: UIScrollView)

  OBJECTIVE-C

  - (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView


  Parameters

  scrollView

  The scroll-view object that is decelerating the scrolling of the content view.

  Discussion

  The scroll view calls this method when the scrolling movement comes to a halt. The decelerating property of UIScrollView controls deceleration.

  Import Statement

  import UIKit

  Availability

  Available in iOS 2.0 and later.

  See Also

  – scrollViewWillBeginDecelerating:

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Managing Zooming

• viewForZoomingInScrollView:

  Asks the delegate for the view to scale when zooming is about to occur in the scroll view.

  Declaration

  SWIFT

  optional func viewForZoomingInScrollView(_ scrollView: UIScrollView) -> UIView?

  OBJECTIVE-C

  - (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView


  Parameters

  scrollView

  The scroll-view object displaying the content view.

  Return Value

  A UIView object that will be scaled as a result of the zooming gesture. Return nil if you don’t want zooming to occur.

  Import Statement

  import UIKit

  Availability

  Available in iOS 2.0 and later.

  See Also

  – scrollViewDidEndZooming:withView:atScale:

• scrollViewWillBeginZooming:withView:

  Tells the delegate that zooming of the content in the scroll view is about to commence.

  Declaration

  SWIFT

  optional func scrollViewWillBeginZooming(_ scrollView: UIScrollView,
                                withView view: UIView!)

  OBJECTIVE-C

  - (void)scrollViewWillBeginZooming:(UIScrollView *)scrollView
                          withView:(UIView *)view


  Parameters

  scrollView	The scroll-view object displaying the content view.
  view	The view object whose content is about to be zoomed.

  Discussion

  This method is called at the beginning of zoom gestures and in cases where a change in zoom level is to be animated. You can use this method to store state information or perform any additional actions prior to zooming the view’s content.

  Import Statement

  import UIKit

  Availability

  Available in iOS 3.2 and later.

• scrollViewDidEndZooming:withView:atScale:

  Tells the delegate when zooming of the content in the scroll view completed.

  Declaration

  SWIFT

  optional func scrollViewDidEndZooming(_ scrollView: UIScrollView,
                             withView view: UIView!,
                              atScale scale: CGFloat)

  OBJECTIVE-C

  - (void)scrollViewDidEndZooming:(UIScrollView *)scrollView
                       withView:(UIView *)view
                        atScale:(CGFloat)scale


  Parameters

  scrollView	The scroll-view object displaying the content view.
  view	The view object representing that part of the content view that needs to be scaled.
  scale	The scale factor to use for scaling; this value must be between the limits established by the UIScrollViewproperties maximumZoomScale and minimumZoomScale.

  Discussion

  The scroll view also calls this method after any “bounce” animations. It also calls this method after animated changes to the zoom level and after a zoom-related gesture ends (regardless of whether the gesture resulted in a change to the zoom level).

  Import Statement

  import UIKit

  Availability

  Available in iOS 2.0 and later.

  See Also

  – viewForZoomingInScrollView:

• scrollViewDidZoom:

  Tells the delegate that the scroll view’s zoom factor changed.

  Declaration

  SWIFT

  optional func scrollViewDidZoom(_ scrollView: UIScrollView)

  OBJECTIVE-C

  - (void)scrollViewDidZoom:(UIScrollView *)scrollView


  Parameters

  scrollView

  The scroll-view object whose zoom factor changed.

  Import Statement

  import UIKit

  Availability

  Available in iOS 3.2 and later.

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Responding to Scrolling Animations

• scrollViewDidEndScrollingAnimation:

  Tells the delegate when a scrolling animation in the scroll view concludes.

  Declaration

  SWIFT

  optional func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView)

  OBJECTIVE-C

  - (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView


  Parameters

  scrollView

  The scroll-view object that is performing the scrolling animation.

  Discussion

  The scroll view calls this method at the end of its implementations of the setContentOffset:animated: and scrollRectToVisible:animated: methods, but only if animations are requested.

  Import Statement

  import UIKit

  Availability

  Available in iOS 2.0 and later.