/*
-tintColor always returns a color. The color returned is the first non-default value in the receiver's superview chain (starting with itself).
If no non-default value is found, a system-defined color is returned.
If this view's -tintAdjustmentMode returns Dimmed, then the color that is returned for -tintColor will automatically be dimmed.
If your view subclass uses tintColor in its rendering, override -tintColorDidChange in order to refresh the rendering if the color changes.
*/
@property(null_resettable, nonatomic, strong) UIColor *tintColor NS_AVAILABLE_IOS(7_0);
/*
-tintAdjustmentMode always returns either UIViewTintAdjustmentModeNormal or UIViewTintAdjustmentModeDimmed. The value returned is the first non-default value in the receiver's superview chain (starting with itself).
If no non-default value is found, UIViewTintAdjustmentModeNormal is returned.
When tintAdjustmentMode has a value of UIViewTintAdjustmentModeDimmed for a view, the color it returns from tintColor will be modified to give a dimmed appearance.
When the tintAdjustmentMode of a view changes (either the view's value changing or by one of its superview's values changing), -tintColorDidChange will be called to allow the view to refresh its rendering.
*/
@property(nonatomic) UIViewTintAdjustmentMode tintAdjustmentMode NS_AVAILABLE_IOS(7_0);
/*
The -tintColorDidChange message is sent to appropriate subviews of a view when its tintColor is changed by client code or to subviews in the view hierarchy of a view whose tintColor is implicitly changed when its superview or tintAdjustmentMode changes.
*/
- (void)tintColorDidChange NS_AVAILABLE_IOS(7_0);
1. tintColor 属性是一个可以影响子控件和自身状态颜色的一个属性例如UIButton(系统样式默认是蓝色的)
2. tintColor 和 tintAdjustmentMode 在发生改变的时候系统会递归调用子类的tintColorDidChange方法，一些系统类实现了这个效果例如 : UIButton，UIStepper, UITextfield, UITextView, UIProgressView, UISegmentedControl, 导航栏和TabBar，ToolBar上的文字和系统的默认图片等
Simulator Screen Shot - iPhone X - 2018-10-16 at 10.48.36.png
