iOS: Change contentsize of a UIScrollview using auto layout

Question

I'm implementing a form inside a UIScrollView. I'm trying to add some space at the bottom of the content of a scroll view when the keyboard is opened so the user can see all the fields. I put the form view inside the UISCrollView adding all the needed constraints with the following code:

 [_infoView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[_infoView(1730)]" options:0 metrics:nil views:views]];

[_scrollView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[_infoView]|" options:0 metrics:nil views:views]];

[_scrollView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[_infoView]|" options:0 metrics:nil views:views]];

[_scrollView addConstraint:[NSLayoutConstraint constraintWithItem:_infoView
                                                        attribute:NSLayoutAttributeCenterX
                                                        relatedBy:NSLayoutRelationEqual
                                                           toItem:_scrollView
                                                        attribute:NSLayoutAttributeCenterX
                                                       multiplier:1
                                                         constant:0]];

As you can see, I specify in the first line the height of the form and the scrollview adapts its content size automatically. Now I want to increase the height of the form, so I've tried to reset the constraint for the height with a greater one but it won't work. Then I've tried to use the [_scrollView setContentSize:] method but this also won't work. Can anyone help me please?

Answer 1

If I understand the problem, I would recommend adjusting the contentInset property on the UIScrollView rather than call layoutSubviews. Note that the docs say:

Use this property to add to the scrolling area around your content. The unit of size is points. The default value is UIEdgeInsetsZero.

You still have to listen for the keyboard hide/show notifications so as to know when to adjust the height of your scrollview:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];

Then in keyboardWillShow you can do this:

UIEdgeInsets insets = UIEdgeInsetsMake(0, 0, 100, 0);
scrollView.contentInset = insets;

100 is the height by which you want to adjust your scrollView. I do this with a UITableView in which I have form elements as UITableViewCells and it works well.