Dynamic Type

Remarks

// Content size category constants
UIContentSizeCategoryExtraSmall
UIContentSizeCategorySmall
UIContentSizeCategoryMedium
UIContentSizeCategoryLarge
UIContentSizeCategoryExtraLarge
UIContentSizeCategoryExtraExtraLarge
UIContentSizeCategoryExtraExtraExtraLarge

// Accessibility sizes
UIContentSizeCategoryAccessibilityMedium
UIContentSizeCategoryAccessibilityLarge
UIContentSizeCategoryAccessibilityExtraLarge
UIContentSizeCategoryAccessibilityExtraExtraLarge
UIContentSizeCategoryAccessibilityExtraExtraExtraLarge

Get the Current Content Size

Swift

UIApplication.sharedApplication().preferredContentSizeCategory

Objective-C

[UIApplication sharedApplication].preferredContentSizeCategory;

This returns a content size category constant, or an accessibility content size category constant.

Handling Preferred Text Size Change Without Notifications on iOS 10

UILabel, UITextField, & UITextView classes have a new property starting from iOS 10 for automatically resizing their font when a user changes their preferred reading size named adjustsFontForContentSizeCategory.

Swift

@IBOutlet var label:UILabel!

if #available(iOS 10.0, *) {
    label.adjustsFontForContentSizeCategory = true
} else {
    // Observe for UIContentSizeCategoryDidChangeNotification and handle it manually
    // since the adjustsFontForContentSizeCategory property isn't available.
}

Matching Dynamic Type Font Size in WKWebView

WKWebView resizes the fonts on web content so that a full-sized web page will fit on the device's form factor. If you want the web text in both portrait and landscape to be similar in size to the user's preferred reading size, you need to set it explicitly.

Swift

// build HTML header for dynamic type and responsive design
func buildHTMLHeader() -> String {
        
    // Get preferred dynamic type font sizes for html styles
    let bodySize = UIFont.preferredFont(forTextStyle: UIFontTextStyle.body).pointSize
    let h1Size = UIFont.preferredFont(forTextStyle: UIFontTextStyle.title1).pointSize
    let h2Size = UIFont.preferredFont(forTextStyle: UIFontTextStyle.title2).pointSize
    let h3Size = UIFont.preferredFont(forTextStyle: UIFontTextStyle.title3).pointSize
        
    // On iPad, landscape text is larger than preferred font size
    var portraitMultiplier = CGFloat(1.0)
    var landscapeMultiplier = CGFloat(0.5)
    
    // iPhone text is shrunken    
    if UIDevice.current.model.range(of: "iPhone") != nil {
        portraitMultiplier = CGFloat(3.0)
        landscapeMultiplier = CGFloat(1.5)
    }
        
    // Start HTML header text
    let patternText = "<html> <head> <style> "
        
    // Match Dynamic Type for this page.
    + "body { background-color: \(backgroundColor);} "
    + "@media all and (orientation:portrait) {img {max-width: 90%; height: auto;} "
    + "p, li { font: -apple-system-body; font-family: Georgia, serif; font-size:calc(\(bodySize * portraitMultiplier)px + 1.0vw); font-weight: normal; color: \(fontColor) } "
    + "h1 { font: -apple-system-headine; font-family: Verdana, sans-serif; font-size:calc(\(h1Size * portraitMultiplier)px + 1.0vw); font-weight: bold; color: \(headFontColor) } "
    + "h2 { font: -apple-system-headine; font-family: Verdana, sans-serif; font-size:calc(\(h2Size * portraitMultiplier)px + 1.0vw); font-weight: bold; color: \(headFontColor) } "
    + "h3, h4 { font: -apple-system-headine; font-family: Verdana, sans-serif; font-size:calc(\(h3Size * portraitMultiplier)px + 1.0vw); font-weight: bold; color: \(headFontColor) } } "
    + "@media all and (orientation:landscape) {img {max-width: 65%; height: auto;}"
    + "p, li { font: -apple-system-body; font-family: Georgia, serif; font-size:calc(\(bodySize * landscapeMultiplier)px + 1.0vw); font-weight: normal; color: \(fontColor) }"
    + "h1 { font: -apple-system-headine; font-family: Verdana, sans-serif; font-size:calc(\(h1Size * landscapeMultiplier)px + 1.0vw); font-weight: bold; color: \(headFontColor) } "
    + "h2 { font: -apple-system-headine; font-family: Verdana, sans-serif; font-size:calc(\(h2Size * landscapeMultiplier)px + 1.0vw); font-weight: bold; color: \(headFontColor) } "
    + "h3, h4 { font: -apple-system-headine; font-family: Verdana, sans-serif; font-size:calc(\(h3Size * landscapeMultiplier)px + 1.0vw); font-weight: bold; color: \(headFontColor) } } </style>"
    + "</head><body>"
    + "<meta name=\"viewport\" content=\"width: device-width\">"
        
    return patternText
}

Text Size Change Notification

You can register for notifications of when the device text size is changed.

Swift

NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(updateFont), name: name:UIContentSizeCategoryDidChangeNotification, object: nil)

Objective-C

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateFont) name:UIContentSizeCategoryDidChangeNotification object:nil];

The notification userInfo object contains the new size under UIContentSizeCategoryNewValueKey.