Layout Anchors, NSLayoutConstraint and Visual Format Language?

Junior PRO

The gist

All three approaches create the same NSLayoutConstraint objects; only the API differs.

Layout Anchors (NSLayoutAnchor, iOS 9+) — the recommended way: view.leadingAnchor.constraint(equalTo:constant:). Type-safe (you cannot tie leadingAnchor to topAnchor — the compiler refuses to mix axes), concise, works with UILayoutGuide (safeAreaLayoutGuide, layoutMarginsGuide, keyboardLayoutGuide).
NSLayoutConstraint(item:attribute:relatedBy:toItem:attribute:multiplier:constant:) — the low-level initializer. Verbose, and mistakes (a wrong attribute) only show up at runtime. Needed when attributes are chosen dynamically.
Visual Format Language (VFL) — an ASCII-art-style string DSL: "H:|-16-[title]-8-[value(>=80)]-16-|". It creates a whole row of constraints at once, but is not type-safe, does not cover multiplier, centerX/Y or safeArea, and string errors crash at runtime. Effectively legacy: new code does not use it, and Swift projects replace it with UIStackView and anchors.

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