UIScrollView and setContentOffset

开发者_JS百科My question is about this method:

(void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated

I have read the documentation, but i don't understand what this method is for.

thanks for your answers.

UIScrollView lets you have content that is larger than what you can view on the screen. In the image below you can see a large red rectangle with a green rectangle inside.

The contentArea property of the UIScrollView defines the logical size of your view (the red rectangle). The visible area of the scroll view is represented by the green rectangle. The contentOffset is the upper left corner of the visible area. Changing contentOffset, the visible area will move around.

(void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated

The method above will move the contentOffset (the upper left corner of the green rectangle) to a specified location, thus moving the visible area (the green rectangle).

Hope this helps.

As mentioned in documentation.

Scrolling to a Specific Offset

Scrolling to a specific top-left location (the contentOffset property) can be accomplished in two ways. The setContentOffset:animated: method scrolls the content to the specified content offset. If the animated parameter is YES, the scrolling will animate from the current position to the specified position at a constant rate. If the animated parameter is NO, the scrolling is immediate and no animation takes place. In both cases, the delegates scrollViewDidScroll: messages. If animation is disabled, or if you set the content offset by setting the contentOffset property directly, the delegate receives a single scrollViewDidScroll: message. If animation is enabled, then the delegate receives a series of scrollViewDidScroll: messages as the animation is in progress. When the animation is complete, the delegate receives a scrollViewDidEndScrollingAnimation: message.

i.e. In simple words if you want to scroll UIScrollView programatically by passing scrolling position values i.e. how much amount to scroll, you can use this method.

This method also calls delegate scrollViewDidScroll: i.e. delegate method of UIScrollView class through which you can maintain the amount of scrolling of UIScrollView.