将UILabel居中于UITableView标头中

Question

I added my UIView as a UITableView header, but when I did, my constraints fell apart. I am trying to have my chapterVerseLabel centered inside the circle as so :

I accomplish this thus so far by doing this :

    var allConstraints = [NSLayoutConstraint]()
    let views = ["tableView" : tableView, "containerView" : containerView, "chapterVerseLabel" : chapterVerseLabel]
    allConstraints += NSLayoutConstraint.constraintsWithVisualFormat("V:|-70-[chapterVerseLabel]-70-|", options: [], metrics: nil, views: views)
    NSLayoutConstraint.activateConstraints(allConstraints)

But I'm not sure how to get it centered as well. It seems all my attempts to center it, don't abide by the stricter rules of centering something within a UITableView Header.

All ideas welcome.

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Update

I tried adding a .CenterX value :

    let leftConstraint = NSLayoutConstraint(item: chapterVerseLabel, attribute: .CenterY, relatedBy: .Equal, toItem: containerView, attribute: .CenterY, multiplier: 1.0, constant: 0.0)
    containerView.addConstraint(leftConstraint)
    let rightConstraint = NSLayoutConstraint(item: chapterVerseLabel, attribute: .CenterX, relatedBy: .Equal, toItem: containerView, attribute: .CenterX, multiplier: 1.0, constant: 0.0)
    containerView.addConstraint(rightConstraint)

But this is the result :

Right now, the chapterVerseLabel sits within my containerView, which is assigned as the tableView.tableHeaderView . Like so :

tableView.tableHeaderView = containerView

Any ideas?

Answer 1

The problem with your constraint are that you have already bounded the label by giving Top and Bottom constraints. Also i dont see leading and trailing constraints You actually have to align the label vertically or horizontally or both based on your requirement.

NSLayoutConstraint *yCS =[NSLayoutConstraint constraintWithItem:chapterVerseLabel attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:containerView attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0.0];
[containerView addConstraint:yCS];

NSLayoutConstraint *xCS =[NSLayoutConstraint constraintWithItem:chapterVerseLabel attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:containerView attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0.0];
[containerView addConstraint:xCS];

Assuming containerView is your header view which gets returned from headerforView delegate method. You need to provide height and width to the label.

Answer 2

There is a uiview at the center. If you want to add a view(1/4) to the circular view at the center you can not do it with the visual format. I assume you want to center chapterVerseLabel . So:

chapterVerseLabel.translatesAutoresizingMaskIntoConstraints = false
yourCircularView.addsubView(chapterVerseLabel)
let xCenterConstraint = NSLayoutConstraint(item: chapterVerseLabel, attribute: .CenterX, relatedBy: .Equal, toItem: view2, attribute: .CenterX, multiplier: 1, constant: 0)
superview.addConstraint(xCenterConstraint)

let yCenterConstraint = NSLayoutConstraint(item: chapterVerseLabel, attribute: .CenterY, relatedBy: .Equal, toItem: view2, attribute: .CenterY, multiplier: 1, constant: 0)
superview.addConstraint(yCenterConstraint)