An instance of the UIButton class implements a button on the touch screen. A button intercepts touch events and sends an action message to a target object when tapped. Methods for setting the target and action are inherited from UIControl. This class PRovides methods for setting the title, image, and other appearance properties of a button. By using these accessors, you can specify a different appearance for each button state.（ios官方文档解释）

Creating Buttons

类方法：buttonWithType:

+ (id)buttonWithType:(UIButtonType)buttonType

参数：

typedef enum {

UIButtonTypeCustom = 0,--No button style

UIButtonTypeSystem,--A system style button, such as those shown in navigation bars and toolbars（Available in iOS 7.0 and later）.

UIButtonTypeDetailDisclosure,--A detail disclosure button

UIButtonTypeInfoLight,--An information button that has a light background

UIButtonTypeInfoDark,--An information button that has a dark background

UIButtonTypeContactAdd,--A contact add button

UIButtonTypeRoundedRect,--A rounded-rectangle style button

} UIButtonType;

Configuring the Button Title

属性：titleLabel:

@property(nonatomic, readonly, retain) UILabel *titleLabel

A view that displays the value of the currentTitle property for a button. (read-only)

Use its own properties primarliy to configure the text of the button.

use the setTitleColor:forState: and setTitleShadowColor:forState: mothods of this class to make those changes.

属性：currentTitle:

@property(nonatomic, readonly, retain) NSString *currentTitle

The value for this property is set automatically whenever the button state changes.

titleForState:

Returns the title associated with the specified state.

- (NSString *)titleForState:(UIControlState)state

参数： UIControlState

方法：- setTitle:forState:

Sets the title to use for the specified state.

- (void)setTitle:(NSString *)title
        forState:(UIControlState)state

方法：attributedTitleForState:

方法：setAttributedTitle:forState

方法：titleColorForState:

方法： setTitleColor:forState:

方法：titleShadowColorForState:

方法：setTitleShadowColor:forState:

属性：reversesTitleShadowWhenHighlighted：

Configuring Button Presentation

属性：adjustsImageWhenHighlighted

A Boolean value that determines whether the image changes when the button is highlighted.

@property(nonatomic) BOOL adjustsImageWhenHighlighted

属性：adjustsImageWhenDisabled

A Boolean value that determines whether the image changes when the button is disabled.

@property(nonatomic) BOOL adjustsImageWhenDisabled

属性：showsTouchWhenHighlighted

A Boolean value that determines whether tapping the button causes it to glow.

@property(nonatomic) BOOL showsTouchWhenHighlighted

backgroundImageForState

imageForState:

setBackgroundImage:forState:

setImage:forState:

属性：tintColor 

文档链接：https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIButton_Class/index.html

参考资料：

 View Programming Guide for iOS.

 Buttons.