View at the bottom in a UIScrollView, with AutoLayout

问题

I'm setting up content in a scroll view with autolayout. The objects in the scrollview are pinned top-to-bottom to the previous one, so that they are under one another. I have a footer view that is added at the end, below these objects.

Here's the catch: when there's few content, the contentView will be smaller than the screen height, so the footer view will appear somewhere in the middle of the screen (which is the normal behavior). But I'd like to prevent that, and make the view stay somewhere at the bottom.

In other words, I would like to setup a double constraint like:

Put this view below all the objects in the scrollview 
AND
keep this view at a distance of max [some number] of the bottom of the screen

In a way that both constraints are always satisfied:

If the height of the content is bigger than the screen, then the view appears at the bottom, after scrolling down
If the height is smaller, then the view is "pinned" to the bottom of the screen, leaving a space relatively big between the bottom of the content and the top of this view

How can I achieve that with AutoLayout?

回答1:

Fairly easy to do with Auto-Layout only... no code required.

The key is to use a "content view" to hold the elements, and a greater-than-or-equal constraint between your "bottom" element and your "footer" view.

In this image, yellow is the main view, green is the scroll view, blue is the content view, the labels are gray and the footer view is pink.

Start with a fresh view controller
add a scroll view, normal constraints (I used 20 all the way around, so we can see the frame)
add a UIView to the scrollView - this will be our "content view"
constrain contentView Top/Bottom/Leading/Trailing all equal to 0 to the scrollView
constrain both the Width and Height of the contentView equal to the scrollView
add your elements - here I used 3 labels
constrain the labels as usual... I used:
- LabelA - Top/Leading/Trailing all at 20, vertical spacing to LabelB of 60
- LabelB - Leading/Trailing at 20, vertical spacing to LabelC of 60
- LabelC - Leading/Trailing at 20
LabelC is also set to Number of Lines: 0 so it will expand with multiple lines of text
Add a UIView as a "footer view" (I stuck a label in it)
constrain the footerView Leading/Trailing/Bottom all at 20 (so we can see the frame)
either set a Height constraint on footerView, or use its content to constrain its height
add a Vertical Spacing constraint from LabelC to footerView, and set it to >= 40
last step, change the Height constraint of contentView to Priority: 250

Now, as you expand/contract the height of LabelC, the footerView will keep at least 40-pts of vertical space. When LabelC gets big enough to "push" footerView below the bottom, scrollView will become scrollable.

Results:

回答2:

you need to check ContentSize of scrollView and modify FooterView Top Constraint with the required Value

My class code

import UIKit

class scrollViewDrag: UIViewController
{
    /// ScrollView Outlet
    @IBOutlet weak var mainScrollView: UIScrollView!

    /// Footer View top spacing constraint
    @IBOutlet weak var footerViewTopConstraint: NSLayoutConstraint!

    /// Used for ScrollView Height
    var screenHeight = CGFloat()

    /// Did Load
    override func viewDidLoad() {
        super.viewDidLoad()

    }

    /// Function used to check for height 
    func checkForHeight(){
        /// Get scrollView Height
        screenHeight = mainScrollView.frame.size.height

        /// Check contentSize Height ?
        if mainScrollView.contentSize.height >= screenHeight {
            /// When ScrollView is having height greater than your scrollView Height
            /// Footer will scroll along other Views
        }
        else{
            /// Issue Case
            let spacingValue = screenHeight-mainScrollView.contentSize.height
            footerViewTopConstraint.constant = spacingValue
        }
    }

    /// Call the height function in DidAppear
    override func viewDidAppear(_ animated: Bool) {
        checkForHeight()
    }
}

Storyboard

I had used Four View with Equal Heights And at last a footerView is attached as Fourth View

FooterView Top Constraint

Top constraint used as footerViewTopConstraint

Output

Case 1 - Size is greater than scrollView Height

Case 2 - Expected Output

来源：https://stackoverflow.com/questions/50847601/view-at-the-bottom-in-a-uiscrollview-with-autolayout

标签

ios