FRStretchImageView

An easy way to add pull-to-stretch UIImageView/UIView on top of your UIScrollView. This is a similar behavior of Twitter Profile’s Header.

Installation

FRStretchImageView is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod "FRStretchImageView"

And then run:

$ pod install

Manual Installation

To manually install FRStretchImageView, simply add FRStretchImageView files to your project.

Example

To run the example project, clone the repo, and run pod install from the Example directory first.

Getting start

First of all, you will need to create & set up the UIScrollView that will be observed in storyboard. For more information about it, check this Natasha The Robot’s tutorial: https://www.natashatherobot.com/ios-autolayout-scrollview/

When you are all set, place your UIImageView/UIView on top of it and pin the NSLayoutConstraint‘s you’ll need. You don’t need to reference them for FRStretchImageView, it will do it for you. But in order to make it work properly, there are only 2 conditions:

1. You need to pin a Top NSLayoutConstraint from your UIImageView/UIView (firstItem) to its superview (it may be the “Content View” UIView of your UIScrollView);

2. You need to pin a Height NSLayoutConstraint in your UIImageView/UIView.

… and subclass it as FRStretchImageView (or FRStretchView).

Usage

Now you’re ready to add the stretching behavior to your UIImageView/UIView! You just need to write a single line to make it work:

myStretchableImage.stretchHeightWhenPulledBy(scrollView: myScroll)

Complete example:

import FRStretchImageView

class MyViewController : UIViewController {
  @IBOutlet weak var myScroll : UIScrollView!
  @IBOutlet weak var myStretchableImage : FRStretchImageView!
  override func viewDidLoad() {
    super.viewDidLoad()
    self.myStretchableImage.stretchHeightWhenPulledBy(scrollView: self.myScroll)
  }
}

You can also add this behavior to an entire UIView:

import FRStretchImageView

class MyViewController : UIViewController {
  @IBOutlet weak var myScroll : UIScrollView!
  @IBOutlet weak var myStretchableView : FRStretchView!
  override func viewDidLoad() {
    super.viewDidLoad()
    self.myStretchableView.stretchHeightWhenPulledBy(scrollView: self.myScroll)
  }
}

If your NSLayoutConstraint doesn’t fill the FRStretchImageView rules, you can now set them manually by adding to your code (from v1.2.0):

self.myStretchableImage.topConstraint = myTopConstraint
self.myStretchableImage.heightConstraint = myHeightConstraint

Note: do this after setting your stretchable scroll, otherwise the initial values will be overrided.

Debug

If you want to receive reports in your log about when the FRStretchImageView is allocated/deallocated or you want to listen your UIScrollView contentOffset updates, turn the debug mode on:

myStretchableImage.debug = true // (or myStretchableView.debug = true)

Troubleshooting

FRStretchImageView can work around your IBOutlets to add its behavior automatically, but it will only wrap the IBOutlets themselves & its superviews. So if you are using multiples UIViews between the UIScrollView and UIImageView/UIView observed, you should set the clipToBounds = false on them.

License

MIT License

Copyright © 2017 Felipe Ricieri

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.