iOS LoginDemo

 //
 //  ViewController.m
 //  FicowLoginDemo1
 //
 //  Created by Ficow on 15/11/12.
 //  Copyright © 2015年 Ficow. All rights reserved.
 //

 #import "ViewController.h"

 @interface ViewController ()
 @property (strong, nonatomic) IBOutlet UITextField *account;
 @property (strong, nonatomic) IBOutlet UITextField *password;
 @property (strong, nonatomic) IBOutlet UIButton *login;
 @property (strong, nonatomic) IBOutlet UIImageView *loginBackground;
 @end

 @implementation ViewController

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

     //Notification监听代码
     [[NSNotificationCenter defaultCenter] addObserver:self
                                              selector:@selector(textFieldDidChange)//监听实现的方法
                                                  name:@"emptyInput"
                                                object:nil];
     NSLog(@"Initiated");
 }

 //实现点击背景隐藏键盘
 - (IBAction)backgroundTap:(id)sender{
     //将View的class设为UIControl
     NSLog(@"ViewTapped");
     [[NSNotificationCenter defaultCenter] postNotificationName:@"emptyInput" object:self];
     [self.account resignFirstResponder];
     [self.password resignFirstResponder];
 }

 //设置键盘的return key为next并跳转到下一个输入框，不要忘了设置return key属性
 - (IBAction)nextInput:(id)sender{
     NSLog(@"AccountInputFinished");
     [[NSNotificationCenter defaultCenter] postNotificationName:@"emptyInput" object:self];
     [self.account resignFirstResponder];
     [self.password becomeFirstResponder];
 }

 //输入结束，跳转到按钮，并点击按钮
 - (IBAction)textFieldDoneEditing:(id)sender{
     [[NSNotificationCenter defaultCenter] postNotificationName:@"emptyInput" object:self];
     [sender resignFirstResponder];
 //    [self.login sendActionsForControlEvents:UIControlEventTouchUpInside];
     NSLog(@"PasswordInputFinished");
 }

 - (void)textFieldDidChange
 {
     NSLog(@"Notification is valid");
     if (self.account.text.length ==  || self.password.text.length == ) {
             self.login.userInteractionEnabled = NO;
             self.login.alpha = 0.5;
             self.loginBackground.alpha = 0.2;
     }
     else{
         self.login.userInteractionEnabled = YES;
         self.login.alpha = 1.0;
         self.loginBackground.alpha = 1.0;
     }
 }

 //错误警告弹出框
 - (void) errorAlert:(id) sender
                    :(NSString *) msg
                    :(NSString *) title{

     UIAlertController *controller = [UIAlertController alertControllerWithTitle:title/*警告框的标题*/ message:msg preferredStyle:UIAlertControllerStyleAlert];
     UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"确定" /*警告框的确定键*/style:UIAlertActionStyleCancel handler:nil];
     [controller addAction:cancelAction];
     [self presentViewController:controller animated:YES completion:nil];
 }

 - (IBAction)checkInput:(id)sender{//定义警告视图

     NSString *msg = nil;
     NSString *title = nil;
     if([self.account.text isEqualToString:@"admin"] &&[self.password.text isEqualToString:@""]){
         msg = [NSString stringWithFormat:@"登录成功！"];
         title = [NSString stringWithFormat:@"Welcome"];
     }//demo1进行账号密码判空的部分
     else{
         if([self.password.text length] ==  || [self.account.text length] == ){
             msg = [NSString stringWithFormat:@"账号/密码不能为空！"];
         }
         else{
             msg = [NSString stringWithFormat:@"账号/密码错误！"];
         }
         title = [NSString stringWithFormat:@"Error"];
     }

     [self errorAlert:sender
                      :msg
                      :title];
 }

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

 @end

可以学习一下使用ReactiveCocoa库来做LoginDemo，很好用哦！