Here's a Swift extension for UILabel. It runs a binary search algorithm to resize the font based off the width and height of the label's bounds. Tested to work with iOS 9 and autolayout.
USAGE: Where <label> is your pre-defined UILabel that needs font resizing
<label>.fitFontForSize()
By Default, this function searches in within the range of 5pt and 300pt font sizes and sets the font to fit its text "perfectly" within the bounds (accurate within 1.0pt). You could define the parameters so that it, for example, searches between 1pt and the label's current font size accurately within 0.1pts in the following way:
<label>.fitFontForSize(1.0, maxFontSize: <label>.font.pointSize, accuracy:0.1)
Copy/Paste the following code into your file
extension UILabel {
func fitFontForSize(var minFontSize : CGFloat = 5.0, var maxFontSize : CGFloat = 300.0, accuracy : CGFloat = 1.0) {
assert(maxFontSize > minFontSize)
layoutIfNeeded() // Can be removed at your own discretion
let constrainedSize = bounds.size
while maxFontSize - minFontSize > accuracy {
let midFontSize : CGFloat = ((minFontSize + maxFontSize) / 2)
font = font.fontWithSize(midFontSize)
sizeToFit()
let checkSize : CGSize = bounds.size
if checkSize.height < constrainedSize.height && checkSize.width < constrainedSize.width {
minFontSize = midFontSize
} else {
maxFontSize = midFontSize
}
}
font = font.fontWithSize(minFontSize)
sizeToFit()
layoutIfNeeded() // Can be removed at your own discretion
}
}
NOTE: Each of the layoutIfNeeded() calls can be removed at your own discretion