Window
A window object has several responsibilities:
- It contains your application’s visible content.
- It plays a key role in the delivery of touch events to your views and other application objects.
- It works with your application’s view controllers to facilitate orientation changes.
you can use your application’s window object to perform a few application-related tasks:
- Use the window object to convert points and rectangles to or from the window’s local coordinate system. For example, if you are provided with a value in window coordinates, you might want to convert it to the coordinate system of a specific view before trying to use it. For information on how to convert coordinates, see Converting Coordinates in the View Hierarchy.
- Use window notifications to track window-related changes. Windows generate notifications when they are shown or hidden or when they accept or resign the key status. You can use these notifications to perform actions in other parts of your application. For more information, see Monitoring Window Changes.
Creating and Configuring a Window
You can create and configure your application’s main window programmatically or using Interface Builder. In either case, you create the window at launch time and should retain it and store a reference to it in your application delegate object. If your application creates additional windows, have the application create them lazily when they are needed. For example, if your application supports displaying content on an external display, it should wait until a display is connected before creating the corresponding window.
You should always create your application’s main window at launch time regardless of whether your application is being launched into the foreground or background. Creating and configuring a window is not an expensive operation by itself. However, if your application is launched straight into the background, you should avoid making the window visible until your application enters the foreground.
Creating Windows in Interface Builder
Creating your application’s main window using Interface Builder is simple because the Xcode project templates do it for you. Every new Xcode application project includes a main nib file (usually with the name MainWindow.xib or some variant thereof) that includes the application’s main window. In addition, these templates also define an outlet for that window in the application delegate object. You use this outlet to access the window object in your code.
Important: When creating your window in Interface Builder, it is recommended that you enable the Full Screen at Launch option in the attributes inspector. If this option is not enabled and your window is smaller than the screen of the target device, touch events will not be received by some of your views. This is because windows (like all views) do not receive touch events outside of their bounds rectangle. Because views are not clipped to the window’s bounds by default, the views still appear visible but events do not reach them. Enabling the Full Screen at Launch option ensures that the window is sized appropriately for the current screen.
If you are retrofitting a project to use Interface Builder, creating a window using Interface Builder is a simple matter of dragging a window object to your nib file. Of course, you should also do the following:
- To access the window at runtime, you should connect the window to an outlet, typically one defined in your application delegate or the File’s Owner of the nib file.
- If your retrofit plans include making your new nib file the main nib file of your application, you must also set the NSMainNibFile key in your application’s Info.plist file to the name of your nib file. Changing the value of this key ensures that the nib file is loaded and available for use by the time the application:didFinishLaunchingWithOptions: method of your application delegate is called.
