IOS 监听slider滑动

// 监听slider滑动
- (IBAction)valueChnage:(UISlider *)sender;
@property (weak, nonatomic) IBOutlet NJView *circleView;

@end

@implementation NJViewController

- (IBAction)valueChnage:(UISlider *)sender {
//    NSLog(@"%.1f", sender.value);
    // 1.传递改变后的值给自定义view
    self.circleView.radius = sender.value;
    // 2.通知自定义view重新绘制图形
//    [self.circleView setNeedsDisplay];

}

- (void)setRadius:(float)radius
{
    _radius = radius;

    // 2.通知自定义view重新绘制图形
    [self setNeedsDisplay];
}

- (void)awakeFromNib
{
    self.radius = ;
}

- (void)drawRect:(CGRect)rect
{
    // 1.获取上下文
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    // 2.绘图
//    CGContextAddEllipseInRect(ctx, CGRectMake(0, 0, 200, 200));
    CGContextAddArc(ctx, , , self.radius, ,  * M_PI, );

    [[UIColor purpleColor] set];
    // 3.渲染
    CGContextFillPath(ctx);

}