原文链接 : 关于 UIControlState 一次神奇的发现
最近发现关于 UIButton 状态的一个挺有意思的问题，大概就是：
当一个按钮处于选中状态，也就是
selected为YES时，如果这时候再点击它时，按钮会变成normal状态时候的样子！
问题效果大概这样：
因为只是个 Demo ，所以代码写的比较随意，就是设置按钮不同状态下的呈现：
#import "ViewController.h"
@interface ViewController ()
@property (strong, nonatomic) UIButton *btn1;
@property (strong, nonatomic) UIButton *btn2;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
UIButton *btn1 = [UIButton buttonWithType:UIButtonTypeCustom];
btn1.frame = CGRectMake(100, 100, 60, 30);
[btn1 setTitle:@"按钮一" forState:UIControlStateNormal];
[btn1 setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
[btn1 setTitleColor:[UIColor redColor] forState:UIControlStateSelected];
[self.view addSubview:_btn1 = btn1];
[btn1 addTarget:self action:@selector(btn1Click) forControlEvents:UIControlEventTouchUpInside];
UIButton *btn2 = [UIButton buttonWithType:UIButtonTypeCustom];
btn2.frame = CGRectMake(170, 100, 60, 30);
[btn2 setTitle:@"按钮二" forState:UIControlStateNormal];
[btn2 setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
[btn2 setTitleColor:[UIColor redColor] forState:UIControlStateSelected];
[self.view addSubview:_btn2 = btn2];
[btn2 addTarget:self action:@selector(btn2Click) forControlEvents:UIControlEventTouchUpInside];
}
- (void)btn1Click {
if(_btn2.isSelected) {_btn2.selected = NO;}
_btn1.selected = YES;
}
- (void)btn2Click {
if(_btn1.isSelected) {_btn1.selected = NO;}
_btn2.selected = YES;
}
@end
我们可以发现，这里分别设置了按钮 UIControlStateNormal和 UIControlStateSelected 状态的标题颜色，那么该如何解决呢？
分别加上这两句就可以了：
[btn1 setTitleColor:[UIColor redColor] forState:UIControlStateSelected|UIControlStateHighlighted];
[btn2 setTitleColor:[UIColor redColor] forState:UIControlStateSelected|UIControlStateHighlighted];
至于为什么，我们可以看看 UIControlState 枚举的定义：
typedef NS_OPTIONS(NSUInteger, UIControlState) {
UIControlStateNormal = 0,
UIControlStateHighlighted = 1 << 0, // used when UIControl isHighlighted is set
UIControlStateDisabled = 1 << 1,
UIControlStateSelected = 1 << 2, // flag usable by app (see below)
UIControlStateFocused NS_ENUM_AVAILABLE_IOS(9_0) = 1 << 3, // Applicable only when the screen supports focus
UIControlStateApplication = 0x00FF0000, // additional flags available for application use
UIControlStateReserved = 0xFF000000 // flags reserved for internal framework use
};
我们可以发现，这是个 NS_OPTIONS 类型的枚举，如果对 NS_OPTIONS 不太理解的，可以去看下叶大的这篇文章里面的解释 SDWebImage源码解析之SDWebImageManager的注解(2)，我这里就不废话了。
既然是 NS_OPTIONS 类型，就表示按钮的状态可能存在多重的情况。比如上面选中状态下再点击，可以理解为 选中|高亮 状态，也就是 UIControlStateSelected|UIControlStateHighlighted。
题外话
这种问题常出现在类似网易新闻 APP 首页的这种界面设计下：
很多大厂的 APP 同样存在这种问题，比如淘宝、京东、新浪微博什么的，搞得我现在每次一看到这种界面，我都会把玩一下，遇到有问题的会心里忍不住吐槽下，没问题的会有种遇到英雄相惜的感觉，哈哈哈，手动滑稽~
