视图之UINavigationController结构解析（侧重于文档分析）
UINavigationController是IOS编程中比较常用的一种容器view controller，很多系统的控件(如UIImagePickerViewController)以及很多有名的APP中(如qq，系统相册等)都有用到。说是使用详解，其实我只会介绍几个自认为比较重要或者容易放错的地方进行讲解，下面让我们挨个探探究竟：
首先上一张图(来自苹果官方文档)：
1、navigationItem
我们都知道navigationItem是UIViewController的一个属性，这个属性是为UINavigationController服务的。文档中是这么解释的“The navigation item used to represent the view controller in a parent’s navigation bar. (read-only)”，即navigation item在navigation Bar代表一个viewController，具体一点儿来说就是每一个加到navigationController的viewController都会有一个对应的navigationItem，该对象由viewController以懒加载的方式创建，稍后我们可以在对象中堆navigationItem进行配置，可以设置leftBarButtonItem, rightBarButtonItem, backBarButtonItem, title以及prompt等属性。前三个每一个都是一个UIBarButtonItem对象，最后两个属性是一个NSString类型描述，注意添加该描述以后NavigationBar的高度会增加30，总的高度会变成74(不管当前方向是Portrait还是Landscape，此模式下navgationbar都使用高度44加上prompt30的方式进行显示)。当然如果觉得只是设置文字的title不够爽，你还可以通过titleview属性指定一个定制的titleview，这样你就可以随心所欲了，当然注意指定的titleview的frame大小，不要显示出界。
举个简单的例子：
[java] view plaincopy// set rightItem UIBarButtonItem *rightItem = [[UIBarButtonItem alloc] initWithTitle:@"Root" style:UIBarButtonItemStyleBordered target:self action:@selector(popToRootVC)]; childOne.navigationItem.rightBarButtonItem = rightItem; [rightItem release]; // when you design a prompt for navigationbar, the hiehgt of navigationbar will becaome 74, ignore the orientation childOne.navigationItem.prompt = @"Hello, im the prompt"; 这段代码设置了navigationItem的rightBarButtonItem，同时设置了prompt信息。
[cpp] view plaincopy/* You may specify the font, text color, text shadow color, and text shadow offset for the title in the text attributes dictionary, using the keys found in UIStringDrawing.h. */ @property(nonatomic,copy) NSDictionary *titleTextAttributes __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_5_0) UI_APPEARANCE_SELECTOR; 它的dictionary的key定义以及其对应的value类型如下：[java] view plaincopy// Keys for Text Attributes Dictionaries // NSString *const UITextAttributeFont; value: UIFont // NSString *const UITextAttributeTextColor; value: UIColor // NSString *const UITextAttributeTextShadowColor; value: UIColor // NSString *const UITextAttributeTextShadowOffset; value: NSValue wrapping a UIOffset struct.
[java] view plaincopyNSDictionary *dict = [NSDictionary dictionaryWithObject:[UIColor yellowColor] forKey:UITextAttributeTextColor]; childOne.navigationController.navigationBar.titleTextAttributes = dict;
[java] view plaincopySvNavChildViewController *childOne = [[SvNavChildViewController alloc] initWithTitle:@"First" content:@"1"]; [self.navigationController pushViewController:childOne animated:NO]; [childOne release]; // raise exception when the stack of navigationbar and navigationController was not correspond [self.navigationController.navigationBar popNavigationItemAnimated:NO];
[cpp] view plaincopy// test ToolBar UIBarButtonItem *one = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:nil action:nil]; UIBarButtonItem *two = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemBookmarks target:nil action:nil]; UIBarButtonItem *three = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAction target:nil action:nil]; UIBarButtonItem *four = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemEdit target:nil action:nil]; UIBarButtonItem *flexItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:nil action:nil]; [childOne setToolbarItems:[NSArray arrayWithObjects:flexItem, one, flexItem, two, flexItem, three, flexItem, four, flexItem, nil]]; [one release]; [two release]; [three release]; [four release]; [flexItem release]; childOne.navigationController.toolbarHidden = NO;
