MonoTouch.UIKit is a binding to CocoaTouch's widget set. Use the classes in this space to create native user interfaces with iOS UIKit.

iOS Applications start as instances of the UIApplication class, they can either be an instance of UIApplication or a subclass of UIKit.UIApplication. This UIApplication object will invoke a number of methods in response to starting up, shutting down, going to the background and other interesting events by calling methods on an instace of the UIKit.UIApplicationDelegate class. Most applications will override the UIKit.UIApplicationDelegate.FinishedLaunching which is responsible for creating the main UIKit.UIWindow and configuring the topmost UIKit.UIViewController to display.

Most applications will create a single UIKit.UIWindow, windows work in concert with UIKit.UIViewController objects which are in charge of orchestrating multiple views, handle rotation and handle various events for the application. This is why on startup, application developers must create both a window and sets its root view controller, like this:

[Register ("AppDelegate")]
public partial class AppDelegate : UIApplicationDelegate
{
	UIWindow window;

	public override bool FinishedLaunching (UIApplication app, NSDictionary options)
	{
		window = new UIWindow (UIScreen.MainScreen.Bounds);
		window.RootViewController = new UIViewController ();
		window.MakeKeyAndVisible ();
		
		return true;
	}
}

Response to user input is implement in UIKit by subclasses of UIKit.UIResponder: UIApplication, UIViewControllers and their subclasses and UIView and their subclasses all inherit from this class.

TextKit

Starting with iOS 7, the text rendering engine exposed on UIKit was upgraded to expose a wide range of typographical capabilities. This functionality was previously only available when using the low-level CoreText APIs. On iOS6, the "AttributedText" property was surfaced and application developers were limited to what was supported by attributed text, with iOS7, developers have access to the "TextStorage" property which provides full control of how things are rendered.

TextKit supports: paginated text, text in columns, text wrapping, rich text editing, interactive text coloring, text folding, custom truncation, and dynamic type.

The TextKit family of APIs provide a modern and sophisticated text layout and rendering engine integrated right into UIKit. This means that you can control the finer details of text rendering on UIKit elements as well as integrating this with animations. Because of this the controls in UIKit support all text attributes and features like kernings and ligatures as well as text effects like Letterpress.

Starting with iOS7 controls like UIKit.UILabel, UIKit.UITextField and UIKit.UITextView are implemented using TextKit directly, the same engine that powers WebKit (the UIKit.UIWebView control).

Dynamic Type

In iOS 7, Apple introduced system-wide dynamic type, a set of fonts optimized for legibility at different magnifications. The end user selects the preferred size of dynamic text in device Settings. Applications receive the ContentizeCategoryChanged notification (see UIKit.UIApplication.Notifications.ObserveContentSizeCategoryChanged) and should reset the font size throughout their application's text views. The system-selected optimal fonts adjust such things as stroke weight and kerning as well as size, so application developers should use UIKit.UIFonts Preferred* properties (e.g., UIKit.UIFont.PreferredBody, UIKit.UIFont.PreferredHeadline, etc. ), as shown in the following example:

UIApplication.Notifications.ObserveContentSizeCategoryChanged((s,e) => {
	SetDynamicTypeFonts();
});

//Call this when initializing, and also in response to ObserveContentSizeCategoryChanged notifications
private void SetDynamicTypeFonts()
{
	headlineLabel.Font = UIFont.PreferredHeadline;
	bodyText.Font = UIFont.PreferredBody;
  //...etc...
}