获取文字  button.currentTitle

更多如下：

@property(nullable, nonatomic,readonly,strong) NSString *currentTitle;             // normal/highlighted/selected/disabled. can return nil

@property(nonatomic,readonly,strong) UIColor  *currentTitleColor;        // normal/highlighted/selected/disabled. always returns non-nil. default is white(1,1)

@property(nullable, nonatomic,readonly,strong) UIColor  *currentTitleShadowColor;  // normal/highlighted/selected/disabled.

@property(nullable, nonatomic,readonly,strong) UIImage  *currentImage;             // normal/highlighted/selected/disabled. can return nil

@property(nullable, nonatomic,readonly,strong) UIImage  *currentBackgroundImage;   // normal/highlighted/selected/disabled. can return nil

@property(nullable, nonatomic,readonly,strong) NSAttributedString *currentAttributedTitle NS_AVAILABLE_IOS(6_0);  // normal/highlighted/selected/disabled. can return nil