What s the UIScrollView contentInset property for

Question

Can someone explain to me what the contentInset property in a UIScrollView instance is used for  And maybe provide an example

User · Accepted Answer

It sets the distance of the inset between the content view and the enclosing scroll view.

Obj-C

aScrollView.contentInset = UIEdgeInsetsMake(0, 0, 0, 7.0);

Swift 5.0

aScrollView.contentInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 7.0)

Here's a good iOS Reference Library article on scroll views that has an informative screenshot (fig 1-3) - I'll replicate it via text here:

  _|?_cW_?_|_?_
   |       | 
---------------
   |content| ?
 ? |content| contentInset.top
cH |content|
 ? |content| contentInset.bottom
   |content| ?
---------------
  _|_______|___ 
             ?


   (cH = contentSize.height; cW = contentSize.width)

The scroll view encloses the content view plus whatever padding is provided by the specified content insets.

User · Answer

Content insets solve the problem of having content that goes underneath other parts of the User Interface and yet still remains reachable using scroll bars   In other words  the purpose of the Content Inset is to make the interaction area smaller than its actual area   Consider the case where we have three logical areas of the screen   TOP BUTTONS  TEXT  BOTTOM TAB BAR   and we want the TEXT to never appear transparently underneath the TOP BUTTONS  but we want the Text to appear underneath the BOTTOM TAB BAR and yet still allow scrolling so we could update the text sitting transparently under the BOTTOM TAB BAR   Then we would set the top origin to be below the TOP BUTTONS  and the height to include the bottom of BOTTOM TAB BAR   To gain access to the Text sitting underneath the BOTTOM TAB BAR content we would set the bottom inset to be the height of the BOTTOM TAB BAR   Without the inset  the scroller would not let you scroll up the content enough to type into it   With the inset  it is as if the content had extra  BLANK CONTENT  the size of the content inset   Blank text has been  inset  into the real  content  -- that s how I remember the concept

User · Answer

It s used to add padding in UIScrollView  Without contentInset  a table view is like this     Then set contentInset   tableView contentInset   UIEdgeInsets top  20  left  0  bottom  0  right  0    The effect is as below     Seems to be better  right   And I write a blog to study the contentInset  criticism is welcome

User · Answer

While jball s answer is an excellent description of content insets  it doesn t answer the question of when to use it  I ll borrow from his diagrams         cW                      ---------------     content        content  contentInset top cH  content      content  contentInset bottom     content    ---------------     content      ------------- -   That s what you get when you do it  but the usefulness of it only shows when you scroll         cW            content    content is still visible ---------------     content        content  contentInset top cH  content      content  contentInset bottom     content    ---------------                                   That top row of content will still be visible because it s still inside the frame of the scroll view  One way to think of the top offset is  how much to shift the content down the scroll view when we re scrolled all the way to the top   To see a place where this is actually used  look at the build-in Photos app on the iphone  The Navigation bar and status bar are transparent  and the contents of the scroll view are visible underneath  That s because the scroll view s frame extends out that far  But if it wasn t for the content inset  you would never be able to have the top of the content clear that transparent navigation bar when you go all the way to the top

User · Answer

Great question   Consider the following example  scroller is a UIScrollView    float offset   1000   super viewDidLoad   for  int i 0 i lt 500  i          UILabel  label      UILabel alloc  initWithFrame CGRectMake i   100  50  95  100   autorelease        label setText  NSString stringWithFormat   label  d  i         self scroller addSubview label        self scroller setContentSize CGSizeMake self view frame size width   2   offset  0         self scroller setContentInset UIEdgeInsetsMake 0  -offset  0  0        The insets are the ONLY way to force your scroller to have a  window  on the content where you want it  I m still messing with this sample code  but the idea is there  use the insets to get a  window  on your UIScrollView

[uiscrollview] What's the UIScrollView contentInset property for?

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