对于UIToolbar，UINavigationBar，UITabBar，UIBarButtonItem，UITabBarItem这几种控件的自定义，因为具备共同性，因此放在一起讨论。
通常有两种方式来实现自定义。
1）获取控件的对象，然后对这个特定的对象进行特定的修改。
2）利用UIAppearance来实现对所有同类控件及特定同类的自定义。因为大多数应用里面的自定义为了美观，基本上相同类的控件自定义方式都一样，因此采用UIAppearance来使得界面的自定义变得非常方便。对于这种方式，通常在AppDelegate.m文件中实现，在
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary*)launchOptions 这个方法内实现。
这里介绍一下UIAppearance的使用，参考自“UIAppearance protocol reference",有两种方式：
1、自定义所有类对象的显示。
[[UINavigationBar appearance] setTintColor:myColor];
2、自定义包含在特定containerclass 的类对象的显示。这主要针对UIBarButtonItem，就是说有的UIBarButtonItem在UINavigationBar中，有的在UIToolbar中，我们可以选择性的对存在于哪个bar中的button进行自定义。举例如下：
[[UIBarButtonItem appearanceWhenContainedIn:[UINavigationBar class], nil]setTintColor:myNavBarColor];
[[UIBarButtonItem appearanceWhenContainedIn:[UINavigationBar class],[UIPopoverController class], nil] setTintColor:myPopoverNavBarColor];
[[UIBarButtonItem appearanceWhenContainedIn:[UIToolbar class], nil] setTintColor:myToolbarColor];
下面总结一下各控件使用UIAppearance自定义的Methods。摘自各苹果官方的Reference.注意下面的方法同样可以单独用于某个单独的对象。
1、UIToolbar
Customizing Appearance
– backgroundImageForToolbarPosition:barMetrics:(page 7)
Returns the image to use for the background in a given position and with given metrics.
– setBackgroundImage:forToolbarPosition:barMetrics:(page 7)
Sets the image to use for the background in a given position and with given metrics.
– shadowImageForToolbarPosition:(page 9)
Returns the image to use for the toolbar shadow in a given position.
– setShadowImage:forToolbarPosition:(page 9)
Sets the image to use for the toolbar shadow in a given position.
tintColor(page 6) property
The color used to tint the bar.
2、UITabBar
Customizing Appearance
backgroundImage (page 5)propertyThe background image for the bar.
selectedImageTintColor (page 7) property
The tint color to apply to the gradient image used when creating the selected image.
selectionIndicatorImage (page 8) propertyThe image used for the selection indicator.
shadowImage (page 8)property
The shadow image to be used for the tab bar.
tintColor (page 8)property
The tint color to apply to the tab bar background.
3、UINavigationBar
Customizing the Bar Appearance
tintColor (page 9)property
The color used to tint the bar.
–backgroundImageForBarMetrics:(page11)
Returns the background image for given bar metrics.
– setBackgroundImage:forBarMetrics:(page 13)Sets the background image for given bar metrics.
– titleVerticalPositionAdjustmentForBarMetrics:(page 14)Returns the title’s vertical position adjustment for given bar metrics.
– setTitleVerticalPositionAdjustment:forBarMetrics:(page 14)Sets the title’s vertical position adjustment for given bar metrics.
titleTextAttributes (page 9) propertyDisplay attributes for the bar’s title text.
4、UIBarButtonItem
Customizing Appearance
tintColor(page 9) property
The tint color for the button item.
– backButtonBackgroundImageForState:barMetrics:(page 10)
Returns the back button background image for a given control state and bar metrics.
– setBackButtonBackgroundImage:forState:barMetrics:(page 17)
Sets the back button background image for a given control state and bar metrics
–backButtonTitlePositionAdjustmentForBarMetrics:(page11)Returns the back button title offset for given bar metrics.
– setBackButtonTitlePositionAdjustment:forBarMetrics:(page 19)Sets the back button title offset for given bar metrics
– backButtonBackgroundVerticalPositionAdjustmentForBarMetrics:(page 10)Returns the back button vertical position offset for given bar metrics.
– setBackButtonBackgroundVerticalPositionAdjustment:forBarMetrics:(page 18)Sets the back button vertical position offset for given bar metrics.
– backgroundVerticalPositionAdjustmentForBarMetrics:(page 13)Returns the background vertical position offset for given bar metrics.
– setBackgroundVerticalPositionAdjustment:forBarMetrics:(page 21)Sets the background vertical position offset for given bar metrics.
–backgroundImageForState:barMetrics:(page11)
Returns the background image for a given state and bar metrics.
– setBackgroundImage:forState:barMetrics:(page 19)
Sets the background image for a given state and bar metrics.
– backgroundImageForState:style:barMetrics:(page 12)
Returns the background image for the specified state, style, and metrics.
– setBackgroundImage:forState:style:barMetrics:(page 20)
Sets the background image for the specified state, style, and metrics.
– titlePositionAdjustmentForBarMetrics:(page 22)Returns the title offset for given bar metrics.
– setTitlePositionAdjustment:forBarMetrics:(page 21)Sets the title offset for given bar metrics.
5、UITabBarItem
Customizing Appearance
– titlePositionAdjustment(page 8)
Returns the offset to use to adjust the title position.
– setTitlePositionAdjustment:(page 8)
Sets the offset to use to adjust the title position.
除此之外，就是针对特定对象进行的自定义了。
1、UITabBarItem
– finishedSelectedImage (page 5)Returns the finished selected image.
– finishedUnselectedImage(page 5)Returns the finished unselected image.
– setFinishedSelectedImage:withFinishedUnselectedImage:(page 7)Sets the finished selected and unselected images.
2、UIBarButtonItem
style (page 8)propertyThe style of the item.
possibleTitles (page 7)property
The set of possible titles to display on the bar button.
width (page 9)propertyThe width of the item.
customView (page 7)property
A custom view representing the item.
3、UINavigationBar
barStyle (page 7)property
The appearance of the navigation bar.
shadowImage (page 8)property
The shadow image to be used for the navigation bar.
translucent (page 10)property
A Boolean value indicating whether the navigation bar is only partially opaque.
基本上，把这些方法搞定，自定义就易如反掌了。