#import <UIKit/UIKit.h>@interface RootViewController : UIViewController@end 

#import "RootViewController.h"#import "NIDropDown.h"@interface RootViewController ()@end@implementation RootViewController- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil{ self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]; if (self) { // Custom initialization } return self;}- (void)viewDidLoad{ [super viewDidLoad]; // Do any additional setup after loading the view.  self.title=@"DropDown";  UIButton *button=[UIButton buttonWithType:UIButtonTypeRoundedRect]; button.frame=CGRectMake(10, 100, 150,30); button.backgroundColor=[UIColor redColor]; [button addTarget:self action:@selector(doClickAction:) forControlEvents:UIControlEventTouchUpInside]; [self.view addSubview:button];    }-(void)doClickAction:(UIButton *)btn{ NSArray *dataArray=[NSArray arrayWithObjects:@"1",@"2",@"3",@"4",@"5", nil];  NIDropDown *dropDown=[[NIDropDown alloc]init]; [dropDown showDropDown:btn andHeight:[dataArray count]*36 andData:dataArray]; [self.view addSubview:dropDown];}