The UINavigationBar class implements a control for navigating hierarchical content in iOS. It’s a bar, typically displayed at the top of the screen, containing buttons for navigating up and down a hierarchy. The primary properties are a left (back) button, a center title, and an optional right button. You can specify custom views for each of these. The most common way to use a navigation bar is in conjunction with a UINavigationController object
A navigation bar enables navigation through an information hierarchy and, optionally, management of screen contents. A navigation bar is contained in a navigation controller, which is an object that manages the display of the hierarchy of custom views. A navigation bar appears at the upper edge of an application screen, just below the status bar.
A navigation bar usually displays the title of the current screen or view, centered along its length. When navigating through a hierarchy of information, users tap the back button to the left of the title to return to the previous screen. Otherwise, users can tap content-specific controls in the navigation bar to manage the contents of the screen.
All controls in a navigation bar include a bezel around them, which, in iOS (ios), is the bordered style. If you place a plain (borderless) control in a navigation bar, it automatically converts to the bordered style.
A navigation bar can be translucent or opaque. If the bar is translucent, the top edge of the main content view meets the bottom edge of the status bar, so that users can see the content behind the navigation bar. If the bar is opaque, the top edge of the main content view meets the bottom edge of the navigation bar.
On iPhone (iphone), changing the device orientation from portrait to landscape can change the height of the navigation bar automatically. On iPad (ipad), the height and translucency of a navigation bar does not change with rotation.
On iPhone, a navigation bar always displays across the full width of the screen. On iPad, a navigation bar can display within a view, such as one pane of a split view, that does not extend across the screen.
