实现alert弹出框

首先需要先实现UIAlertViewDelegate协议，这样可以获得Alert各种方法并且可以实现他
看例子！

//
//  ViewController.h
//  LoginQQ
//
//  Created by Rayln Guan on 9/16/13.
//  Copyright (c) 2013 Rayln Guan. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController <UIAlertViewDelegate>
@property (nonatomic, assign) IBOutlet UITextField *username;
@property (nonatomic, assign) IBOutlet UITextField *password;

-(IBAction)login;

@property (nonatomic, assign) IBOutlet UILabel *qq;

@end

//
//  ViewController.m
//  LoginQQ
//
//  Created by Rayln Guan on 9/16/13.
//  Copyright (c) 2013 Rayln Guan. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)login{
    NSLog(@"点击了: %@, %@", self.username.text, self.password.text);
    self.qq.text = @"rayln";
    //即username控件不想当第一响应者，所以键盘会收回去
    //[self.username resignFirstResponder];
    
    //如果第一响应者在view中，可以调用
    [self.view endEditing:YES];
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"title" message:@"testcontext" delegate:self cancelButtonTitle:@"cancel" otherButtonTitles:@"otherbtn", nil];
    [alert show];
    [alert release];
}

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex{
    NSLog(@"%i", buttonIndex);
}


- (void)viewDidLoad
{
    [super viewDidLoad];
	// Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end