Xamarin.iOS Auto Layout in Xamarin.iOS Adding Constraints Using Visual Format Language (VFL)
Example
// Using Visual Format Language requires a special look-up dictionary of names<->views.
var views = new NSDictionary(
nameof(someLabel), someLabel,
nameof(anotherLabel), anotherLabel,
nameof(oneMoreLabel), oneMoreLabel
);
// It can also take a look-up dictionary for metrics (such as size values).
// Since we are hard-coding those values in this example, we can give it a `null` or empty dictionary.
var metrics = (NSDictionary)null;
// Add the vertical constraints to stack everything together.
// `V:` = vertical
// `|…|` = constrain to super view (`View` for this example)
// `-10-` = connection with a gap of 10 pixels (could also be a named parameter from the metrics dictionary)
// `-[viewName]-` = connection with a control by name looked up in views dictionary (using C# 6 `nameof` for refactoring support)
var verticalConstraints = NSLayoutConstraint.FromVisualFormat(
$"V:|-20-[{nameof(someLabel)}]-6-[{nameof(anotherLabel)}]-6-[{nameof(oneMoreLabel)}]->=10-|",
NSLayoutFormatOptions.AlignAllCenterX,
metrics,
views
);
View.AddConstraints(verticalConstraints);
You may find some constraint types, like aspect ratios, cannot be conveyed in Visual Format Language (VFL) syntax and must call the appropriate methods directly.
