@interface HLProgressView : UIView
@property (nonatomic, assign) CGSize viewSize;
@end

@implementation HLProgressView
- (instancetype)initWithFrame:(CGRect)frame{
    self = [super initWithFrame:frame];
    if (self) {
    }
    return self;
}
- (void)setViewSize:(CGSize)viewSize {
    _viewSize = viewSize;
    self.frame = CGRectMake(0, 0, viewSize.width, viewSize.height);
    // setNeedsDisplay會(huì)自動(dòng)調(diào)用drawRect方法
    [self setNeedsDisplay];
}
- (void)drawRect:(CGRect)rect {
    CGSize size = self.bounds.size;
    // 獲取圖形上下文對象CGContextRef
    CGContextRef context = UIGraphicsGetCurrentContext();
    // 創(chuàng)建一個(gè)顏色空間
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    // 設(shè)置的顏色 每四個(gè)元素表示一種顏色，值的范圍0~1，分別表示R、G、B、透明度 
    CGFloat colors[] = {
        55.0/255.0, 180.0/255.0, 255.0/255.0, 1.0,
        55.0/255.0, 80.0/255.0, 255.0/255.0, 1.0
    };
    // 漸變的位置信息范圍0~1 0表示開始的位置 1表示結(jié)束的位置
    CGFloat gradientLocations[] = {0, 1};
    // 漸變的個(gè)數(shù)
    size_t locationCount = 2;
    // 創(chuàng)建漸變
    CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace, colors, gradientLocations, locationCount);
    // 指定漸變的開始位置和結(jié)束位置 這里設(shè)置完效果是整塊區(qū)域的水平方向的漸變
    CGPoint gradientStartPoint = CGPointMake(0, size.height/2);
    CGPoint gradientEndPoint = CGPointMake(size.width, size.height/2);
    // 將漸變畫到上下文中，最后一個(gè)參數(shù)表示發(fā)散的方式
    CGContextDrawLinearGradient(context, gradient, gradientStartPoint, gradientEndPoint, kCGGradientDrawsBeforeStartLocation);
    // 釋放內(nèi)存
    CGGradientRelease(gradient);
    CGColorSpaceRelease(colorSpace);
}
@end

@interface UICustomSlider : UIView
@end

@interface UICustomSlider ()
@property (nonatomic, strong) HLProgressView *progressView;
@end
@implementation UICustomSlider
- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor grayColor];
        self.clipsToBounds = YES; //不顯示超過父視圖的內(nèi)容
        self.layer.cornerRadius = 8;
        self.progressView = [[HLProgressView alloc] initWithFrame:CGRectMake(0, 0, 140, 44)];
        [self addSubview:self.progressView];
    }
    return self;
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    CGPoint point = [touches.anyObject locationInView:self];
    self.progressView.viewSize = CGSizeMake(point.x, self.bounds.size.height);
}
- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    CGPoint point = [touches.anyObject locationInView:self];
    self.progressView.viewSize = CGSizeMake(point.x, self.bounds.size.height);
}
- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    CGPoint point = [touches.anyObject locationInView:self];
    self.progressView.viewSize = CGSizeMake(point.x, self.bounds.size.height);
}
@end

#import "GradientSlider.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    UICustomSlider *customSlider = [[UICustomSlider alloc] initWithFrame:CGRectMake(20, 100, 280, 44)];
    [self.view addSubview:customSlider];
}