DrawView.h

typedef void(^DrawView_DrawBlock)(UIView* v,CGContextRef context);

@interface DrawView : UIView
@property (nonatomic,copy) DrawableView_DrawBlock drawBlock;
@end

DrawView.m

#import "DrawView.h"

@implementation DrawView
@synthesize drawBlock;

- (void)dealloc
{
    [drawBlock release], drawBlock = nil;
    [super dealloc];
}

- (void)drawRect:(CGRect)rect
{
    [super drawRect:rect];
    
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    if(self.drawBlock)
        self.drawBlock(self,context);
}

@end

gistfile1.m

DrawView* drawableView = [[[DrawView alloc] initWithFrame:CGRectMake(0,0,320,50)] autorelease];
drawableView.drawBlock = ^(UIView* v,CGContextRef context)
{
    CGPoint startPoint = CGPointMake(0,v.bounds.size.height-1);
    CGPoint endPoint = CGPointMake(v.bounds.size.width,v.bounds.size.height-1);

    CGContextSetStrokeColorWithColor(context, [UIColor grayColor].CGColor);
    CGContextSetLineWidth(context, 1);
    CGContextMoveToPoint(context, startPoint.x + 0.5, startPoint.y + 0.5);
    CGContextAddLineToPoint(context, endPoint.x + 0.5, endPoint.y + 0.5);
    CGContextStrokePath(context);
};
[self.view addSubview:drawableView];