很多时候，不同的类之间需要有数值交流传递，但是这些类之间并没有直接的关系，比如当一个界面向子页面传递某个参数，而子页面修改某些值之后而再返回主页面的时候，主页面的UI需要根据子页面的状态做一定的UI更新，这时，就需要考虑参数传递的问题了。这里使用IOS的代理的特点，以担当参数传递的职责。
@protocol UserInfoDelegate <NSObject> @required /** * 获取用户Id * * @return 用户ID */ - (NSString*)userId; @optional /** * 默认头像 */ - (void) setPortraitPath:(NSString*)portrait; @end该协议有两个方法，方法userId是用于传进参数，方法setPortraitPath:用于传出参数，这两个方法都是由使用了该协议（不是实现了该协议）的类调用，调用的大致方法如下：
- (void)viewDidLoad
{
[super viewDidLoad];
self.view.backgroundColor = [UIColor whiteColor];
UILabel* userLabel = [[UILabel alloc] init];
userLabel.frame = CGRectMake(40, 200, 200, 30);
// 设置了代理
if ([_delegate respondsToSelector:@selector(userId)])
{
userLabel.text = [_delegate userId];
}
else
{
userLabel.text = @"Delegate not set";
}
/** 中间代码略 */
// 更新对应代理的头像
if ([_delegate respondsToSelector:@selector(userId)])
{
[_delegate setPortraitPath:imagePath];
}
}上述代码中使用方法respondsToSelector是查看是否实现了该方法，需要注意的是，这里调用的两个方法都是在实现了代理协议的类里面实现的，而不是当前类实现。需要注意用户信息类要有属性或者变量类型为id<UserInfoDelegate>的，如下所示：@interface UserInfo : UIViewController @property (nonatomic, strong) id<UserInfoDelegate> delegate; @end
#pragma 实现协议UserInfoDelegate
// 当前视图的值传值给对方
- (NSString*)userId
{
return _userText.text;
}
// 对方视图的值传值到本类
- (void) setPortraitPath:(NSString*)portrait
{
if (portrait == nil)
{
portrait = [[NSBundle mainBundle] pathForResource:@"boy0" ofType:@"png"];
}
// 设置头像
_portraitView.image = [UIImage imageWithData:[NSData dataWithContentsOfFile:portrait]];
}然后在转入子页面的时候，设置子页面的代理为当前实例，如此完成了整个部分的参数传值过程。- (void)goUser
{
UserInfo* user = [[UserInfo alloc] init];
// 设置代理
user.delegate = self;
[self.navigationController pushViewController:user animated:YES];
}// Copyright (c) 2015年 arbboter. All rights reserved. // #import <UIKit/UIKit.h> @protocol UserInfoDelegate <NSObject> @required /** * 获取用户Id * * @return 用户ID */ - (NSString*)userId; @optional /** * 默认头像 */ - (void) setPortraitPath:(NSString*)portrait; @end @interface UserInfo : UIViewController @property (nonatomic, strong) id<UserInfoDelegate> delegate; @end
// Copyright (c) 2015年 arbboter. All rights reserved.
//
#import "UserInfo.h"
@implementation UserInfo
- (void)viewDidLoad
{
[super viewDidLoad];
self.view.backgroundColor = [UIColor whiteColor];
UILabel* userLabel = [[UILabel alloc] init];
userLabel.frame = CGRectMake(40, 200, 200, 30);
// 设置了代理
if ([_delegate respondsToSelector:@selector(userId)])
{
userLabel.text = [_delegate userId];
}
else
{
userLabel.text = @"Delegate not set";
}
userLabel.layer.borderWidth = 1;
userLabel.textAlignment = NSTextAlignmentCenter;
[self.view addSubview:userLabel];
UILabel* nameLabel = [[UILabel alloc] init];
nameLabel.frame = CGRectMake(40, 240, 200, 30);
nameLabel.layer.borderWidth = 1;
nameLabel.textAlignment = NSTextAlignmentCenter;
nameLabel.text = [NSString stringWithFormat:@"name_%d", arc4random()];
[self.view addSubview:nameLabel];
UILabel* stateLabel = [[UILabel alloc] init];
stateLabel.frame = CGRectMake(40, 280, 200, 30);
stateLabel.layer.borderWidth = 1;
stateLabel.text = @"该家伙太懒了，什么都没有留下。请邀请ta更新....";
// 高度自适应
stateLabel.numberOfLines = 0;
[stateLabel sizeToFit];
[self.view addSubview:stateLabel];
UIImageView* portrait = [[UIImageView alloc] init];
portrait.frame = CGRectMake(100, 80, 100, 100);
portrait.layer.borderWidth = 1;
NSString* imagePath = [[NSBundle mainBundle] pathForResource:userLabel.text ofType:@"png"];
if(imagePath == nil)
{
imagePath = [[NSBundle mainBundle] pathForResource:@"boy3" ofType:@"png"];
userLabel.text = @"user not exist";
}
portrait.image = [UIImage imageWithData:[NSData dataWithContentsOfFile:imagePath]];
portrait.contentMode = UIViewContentModeScaleAspectFit;
[self.view addSubview:portrait];
// 更新对应代理的头像
if ([_delegate respondsToSelector:@selector(userId)])
{
[_delegate setPortraitPath:imagePath];
}
}
@end
// Copyright (c) 2015年 arbboter. All rights reserved.
//
#import "ViewController.h"
@interface ViewController ()
@property (nonatomic, strong) UIImageView* portraitView;
@property (nonatomic, strong) UITextField* userText;
@end
@implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
self.view.backgroundColor = [UIColor whiteColor];
[super.navigationController setNavigationBarHidden:YES animated:TRUE];
//[super.navigationController setToolbarHidden:YES animated:TRUE];
_portraitView = [[UIImageView alloc] init];
_portraitView.frame = CGRectMake(100, 40, 150, 150);
[self.view addSubview:_portraitView];
UILabel* userLabel = [[UILabel alloc] init];
userLabel.frame = CGRectMake(40, 200, 60, 30);
userLabel.text = @"用户ID";
[self.view addSubview:userLabel];
_userText = [[UITextField alloc] init];
_userText.frame = CGRectMake(100, 200, 200, 30);
_userText.placeholder = @"请输入用户ID";
_userText.returnKeyType = UIReturnKeyGo;
_userText.layer.borderWidth = 1;
[_userText addTarget:self action:@selector(goUser) forControlEvents:UIControlEventEditingDidEndOnExit];
[self.view addSubview:_userText];
_portraitView = [[UIImageView alloc] init];
_portraitView.frame = CGRectMake(100, 80, 100, 100);
_portraitView.contentMode = UIViewContentModeScaleAspectFit;
[self.view addSubview:_portraitView];
[self setPortraitPath:nil];
}
- (void)goUser
{
UserInfo* user = [[UserInfo alloc] init];
// 设置代理
user.delegate = self;
[self.navigationController pushViewController:user animated:YES];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (void) viewWillAppear:(BOOL)animated
{
// 隐藏导航栏
[super.navigationController setNavigationBarHidden:YES animated:animated];
}
- (void) viewWillDisappear:(BOOL)animated
{
// 显示导航栏
[super.navigationController setNavigationBarHidden:NO animated:animated];
}
#pragma 实现协议UserInfoDelegate
// 当前视图的值传值给对方
- (NSString*)userId
{
return _userText.text;
}
// 对方视图的值传值到本类
- (void) setPortraitPath:(NSString*)portrait
{
if (portrait == nil)
{
portrait = [[NSBundle mainBundle] pathForResource:@"boy0" ofType:@"png"];
}
// 设置头像
_portraitView.image = [UIImage imageWithData:[NSData dataWithContentsOfFile:portrait]];
}
@end原文地址：http://blog.csdn.net/arbboter/article/details/42554875
