ios 自顶一个view

//
//  YKPopView.m
//  DrawAnSample
//
//  Created by 高顺生 on 15/9/6.
//  Copyright (c) 2015年 yinyakun. All rights reserved.
//

#import "YKPopView.h"
#define MENUGAP 7

@implementation YKPopView

-(instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor clearColor];
    }
    return self;
}

// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
    // Drawing code
    CGFloat width = rect.size.width;
    CGFloat height = rect.size.height;
    CGFloat radius = 3;
    
    // 获取CGContext，注意UIKit里用的是一个专门的函数
    CGContextRef context = UIGraphicsGetCurrentContext();
    // 移动到初始点
    CGContextMoveToPoint(context, radius, MENUGAP);
    
    // 绘制第1条线和第1个1/4圆弧
    CGContextAddLineToPoint(context, width * 5/6 - 6,MENUGAP);
    CGContextAddLineToPoint(context, width * 5/6,0);
    CGContextAddLineToPoint(context, width  * 5/6 + 6,MENUGAP);
    CGContextAddLineToPoint(context, width - radius, MENUGAP);
    CGContextAddArc(context, width - radius, radius + MENUGAP, radius, -0.5 * M_PI, 0.0, 0);
    
    // 绘制第2条线和第2个1/4圆弧
    CGContextAddLineToPoint(context, width, height - radius - MENUGAP);
    CGContextAddArc(context, width - radius, height - radius - MENUGAP, radius, 0.0, 0.5 * M_PI, 0);
    
    // 绘制第3条线和第3个1/4圆弧
    CGContextAddLineToPoint(context, radius, height - MENUGAP);
    CGContextAddArc(context, radius, height - radius - MENUGAP, radius, 0.5 * M_PI, M_PI, 0);
    
    // 绘制第4条线和第4个1/4圆弧
    CGContextAddLineToPoint(context, 0, radius + MENUGAP);
    CGContextAddArc(context, radius, radius + MENUGAP, radius, M_PI, 1.5 * M_PI, 0);
    
    // 闭合路径
    CGContextClosePath(context);
    
    [[UIColor redColor] setFill];
    CGContextDrawPath(context, kCGPathFill);

}

　　自定义一个view.