How to set content size of UIScrollView dynamicall

问题:

I got question about UIScrollview.

The story is I have a UIView named ChartsView which I re-draw it myself by override method drawRect(). The content of drawing was generated dynamically. So I do not know its size until runtime. The question is how/where can I set its super view's (scrollView) content size dynamically?Any idea about that?

    - (void)viewDidLoad
    {
        [super viewDidLoad];

// not this way. it's fixed size.....
        ChartsView *chartsView = [[ChartsView alloc]initWithFrame:CGRectMake(0, 0, 320, 800)]; 

        self.scrollView.contentSize = chartsView.frame.size;

        [self.scrollView addSubview:chartsView];

    }

回答1:

One more easy way

- (void)viewDidLoad
{
    float sizeOfContent = 0;
    UIView *lLast = [scrollView.subviews lastObject];
    NSInteger wd = lLast.frame.origin.y;
    NSInteger ht = lLast.frame.size.height;

    sizeOfContent = wd+ht;

    scrollView.contentSize = CGSizeMake(scrollView.frame.size.width, sizeOfContent);
}

回答2:

swift (2.0)

@IBOutlet weak var btnLatestButton: UIButton!

override func viewDidLoad() {
    super.viewDidLoad()

    let height = btnLatestButton.frame.size.height
    let pos = btnLatestButton.frame.origin.y
    let sizeOfContent = height + pos + 10
    scrollview.contentSize.height = sizeOfContent

}

Above ofcourse is when you just have a fixed amount of views on your scrollview. IOS Rocks method is available but was not good for me, created more space then I needed.

    let lastView : UIView! = scrollview.subviews.last
    let height = lastView.frame.size.height
    let pos = lastView.frame.origin.y
    let sizeOfContent = height + pos + 10
    scrollview.contentSize.height = sizeOfContent

回答3:

Thanks to IOS Rocks and CularBytes for the leads on this. I found two problems (for me) with the above solutions:

1. I always have a container UIView as the only child of my UIScrollView, so I had to update the way I look up the last view in that child UIView (see below)
2. I am offset'ing my content in the UIScrollView and as such needed to calculate the absolute position of that last UIView (so, relative to the window not the parent view)

Also I am using autolayout to pin the sides of the UIScrollView, so I don't need to worry about width (as is CularBytes).

Here's what I came up with and works (in Swift 3.0):

func setScrollViewContentSize() {

    var height: CGFloat
    let lastView = self.myScrollView.subviews[0].subviews.last!
    print(lastView.debugDescription) // should be what you expect

    let lastViewYPos = lastView.convert(lastView.frame.origin, to: nil).y  // this is absolute positioning, not relative
    let lastViewHeight = lastView.frame.size.height

    // sanity check on these
    print(lastViewYPos)
    print(lastViewHeight)

    height = lastViewYPos + lastViewHeight

    print("setting scroll height: \(height)")

    myScrollView.contentSize.height = height
}

I call this in my viewDidAppear() method.

回答4:

It is not 100% guaranteed that the last object in scrollView.subviews array will return the highest y-origin object in your scroll view. The subviews array is arranged by Z-Index (i.e the last object in the subviews array will be the object stacked the highest and will be the top-most subview in the scroll view's subviews. Instead it is more accurate to use a basic sort function to iterate through the subviews and get the object with the highest y-origin.

Here is a basic function in swift 3 that that can do so:

func calculateContentSize(scrollView: UIScrollView) -> CGSize {
    var topPoint = CGFloat()
    var height = CGFloat()

    for subview in scrollView.subviews {
        if subview.frame.origin.y > topPoint {
            topPoint = subview.frame.origin.y
            height = subview.frame.size.height
        }
    }
    return CGSize(width: scrollView.frame.size.width, height: height + topPoint)
}

Usage (in viewDidLayoutSubviews or whenever your content size updates):

scrollView.contentSize = calculateContentSize(scrollView: scrollView)

UPDATE SWIFT 4

Here is a more consise version in swift 4

extension UIScrollView {
    func updateContentView() {
        contentSize.height = subviews.sorted(by: { $0.frame.maxY < $1.frame.maxY }).last?.frame.maxY ?? contentSize.height
    }
}

Usage:

myScrollView.updateContentView()

回答5:

try this

- (void)viewDidLoad
        {
            [super viewDidLoad];

    // not this way. it's fixed size.....
            ChartsView *chartsView = [[ChartsView alloc]initWithFrame:CGRectMake(0, 0, 320, 800)]; 

            self.scrollView.contentSize = chartsView.frame.size;
            [self.scrollView setNeedsDisplay];
            [self.scrollView addSubview:chartsView];

    }

回答6:

Try this -

- (void)viewDidLoad
    {
        [super viewDidLoad];

// not this way. it's fixed size.....
        ChartsView *chartsView = [[ChartsView alloc]initWithFrame:CGRectMake(0, 0, 320, 800)]; 

        //self.scrollView.contentSize = chartsView.frame.size;
        [self.scrollView setContentSize:CGSizeMake(chartsView.frame.size.width, chartsView.frame.size.height)];
        [self.scrollView addSubview:chartsView];

    }

回答7:

This is an extension written on Swift 3

extension UIScrollView {
    func updateContentViewSize() {
        var newHeight: CGFloat = 0
        for view in subviews {
            let ref = view.frame.origin.y + view.frame.height
            if ref > newHeight {
                newHeight = ref
            }
        }
        let oldSize = contentSize
        let newSize = CGSize(width: oldSize.width, height: newHeight + 100)
        contentSize = newSize
    }
}