自定义UISwitch，可实现自定义开关图片和背景色

效果如图所示：

iOS7.0之后无法自定义UISwitch的图片，而在日常的开发需求中，又不可能只有一种开关样式，UI所设计的开关样式千奇百怪，那么系统所提供的开关样式已经不足以满足我们的开发需求了。所以这时候我们就需要自定义开关了。
自定义开关，我们剖析下开关的结构，在系统的UISwitch中，我们可以看出，通过调用 onImage 或者 offImage 属性来设置开关的图片，但是这两个方法在 iOS 6 之后已经被弃用掉了。

NS_CLASS_AVAILABLE_IOS(2_0) __TVOS_PROHIBITED @interface UISwitch : UIControl <NSCoding>

@property(nullable, nonatomic, strong) UIColor *onTintColor NS_AVAILABLE_IOS(5_0) UI_APPEARANCE_SELECTOR;
@property(null_resettable, nonatomic, strong) UIColor *tintColor NS_AVAILABLE_IOS(6_0);
@property(nullable, nonatomic, strong) UIColor *thumbTintColor NS_AVAILABLE_IOS(6_0) UI_APPEARANCE_SELECTOR;

@property(nullable, nonatomic, strong) UIImage *onImage NS_AVAILABLE_IOS(6_0) UI_APPEARANCE_SELECTOR;
@property(nullable, nonatomic, strong) UIImage *offImage NS_AVAILABLE_IOS(6_0) UI_APPEARANCE_SELECTOR;

@property(nonatomic,getter=isOn) BOOL on;

- (instancetype)initWithFrame:(CGRect)frame NS_DESIGNATED_INITIALIZER;      // This class enforces a size appropriate for the control, and so the frame size is ignored.
- (nullable instancetype)initWithCoder:(NSCoder *)aDecoder NS_DESIGNATED_INITIALIZER;

- (void)setOn:(BOOL)on animated:(BOOL)animated; // does not send action
@end

那么，我们自定义开关所要暴露出来的属性就要有

• 开关开着时的图片
• 开关关着时的图片
• 开关的背景色

• 开关的状态
  在这里，我们可以将开关分为如图所示两部分结构：

  
  自定义开关结构
  

  其中，B为开关提供底部背景色值，A为开关提供开关状态色值，点击开关，A可以左右滑动，并改变状态。

思路：

• 添加点击事件，改变自身状态
• 添加观察者观察自身状态的改变
• 通过判断自身状态，显示自身样式

主要代码如下所示：

@interface BKSwitch : UIControl
@property (nonatomic, assign) BOOL on;
@property (nonatomic, strong) UIView *roundView;//滑块view
@end


@implementation BKSwitch

- (instancetype)initWithFrame:(CGRect)frame{
    if (self = [super initWithFrame:frame]) {
        [self addObserver:self forKeyPath:@"isOn" options:NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew context:nil];
        [self addTarget:self action:@selector(translateAni) forControlEvents:UIControlEventTouchUpInside];
        [self creatView];
    }
    return self;
}

-(void)creatView{
    self.backgroundColor = [UIColor whiteColor];
    self.clipsToBounds = YES;
    self.layer.cornerRadius = self.bounds.size.height/2;
    self.layer.borderColor = [UIColor grayColor].CGColor;
    self.layer.borderWidth = .5;
    
    self.roundView = [[UIView alloc]initWithFrame:CGRectMake(0, 1, self.bounds.size.height-2, self.bounds.size.height-2)];
    self.roundView.layer.cornerRadius = self.bounds.size.height/2;
//    self.roundView.backgroundColor = [UIColor whiteColor];
    self.roundView.userInteractionEnabled = NO;
    [self addSubview:self.roundView];
//    self.roundView.layer.shadowColor = [UIColor blackColor].CGColor;//shadowColor阴影颜色
//    self.roundView.layer.shadowOffset = CGSizeMake(0,0);//shadowOffset阴影偏移,x向右偏移4，y向下偏移4，默认(0, -3),这个跟shadowRadius配合使用
//    self.roundView.layer.shadowOpacity = 0.5;//阴影透明度，默认0
//    self.roundView.layer.shadowRadius = 2;//阴影半径，默认3
}

-(void)setOn:(BOOL)on{
    if (on) {
        self.roundView.frame = CGRectMake(self.bounds.size.width-self.roundView.bounds.size.width-1, 1,           self.bounds.size.height-2, self.bounds.size.height-2);
        self.roundView.roundView.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"switchOn"]];
        self.roundView.backgroundColor = OCTColorFromRGB(0xffe100);
        self.roundView.layer.borderColor = OCTColorFromRGB(0xffe100).CGColor;
    }else{
        self.roundView.frame = CGRectMake(0, 1, self.bounds.size.height-2, self.bounds.size.height-2);
        self.roundView.roundView.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"switchOff"]];
        self.roundView.backgroundColor = OCTColorFromRGB(0xc9c9c9);
        self.roundView.layer.borderColor = OCTColorFromRGB(0xc9c9c9).CGColor;
    }
    self.isOn = on;
}

-(BOOL)on{
    return self.isOn;
}

- (void)translateAni{
    CGRect rect = self.roundView.frame;
    [UIView animateWithDuration:0.3 animations:^{
        self.roundView.frame = rect;
    }];
    if (!self.isOn){
        rect.origin.x = self.bounds.size.width - self.roundView.bounds.size.width - 1;
    }else{
        rect.origin.x = 0;
    }
    [UIView animateWithDuration:0.3 animations:^{
        self.roundView.frame = rect;
    }completion:^(BOOL finished) {
    }];
    self.isOn = !self.isOn;
}

//监听isON
//keyPath:属性名称
//object:被观察的对象
//change:变化前后的值都存储在change字典中
//context:注册观察者时，context传过来的值
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context
{
    [self sendActionsForControlEvents:UIControlEventValueChanged];
}

-(void)dealloc
{
    [self removeObserver:self forKeyPath:@"isOn"];
}

@end