尝试过以下几种方式都不太理想：

• 不对接口名作定义，直接编写字符串
  缺点：没有统一管理的地方，接口值散落，同一接口多处使用时不易维护，易拼写错误；接口值作为数据资源不应直接混入逻辑代码中

NSString *urlString = [NSString stringWithFormat:@"%@%@", @"http://www.baidu.com/", @"app/login"];

• 宏定义接口名
  缺点：接口各自定义，没有形成集合或类型。在把接口作为参数传值时，只能以字符串为类型接收。

#define ServerHost @"http://www.baidu.com/"
#define ServerApiLogin @"app/login"
NSString *urlString = [NSString stringWithFormat:@"%@%@", ServerHost, ServerApiLogin];

• 用枚举定义接口名+plist文件映射存储接口字符串
  缺点：枚举值是整型，导致接口多了顺序属性，顺序或者说索引并不是接口应该含有需要的东西，反而会成为累赘，不利于接口集的增删插入

// ServerApi.plst存储了接口字符串数组
NSURL *url = [[NSBundle mainBundle] URLForResource:@"ServerApi" withExtension:@"plist"];
NSArray *array = [NSArray arrayWithContentsOfURL:url];
NSString *api = array[ServerApi];
NSString *urlString = [NSString stringWithFormat:@"%@%@", ServerHost, api];

使用字符串常量+类型定义

这是参考苹果API的定义方式

//
//  JXRequester.h
// 
#import <UIKit/UIKit.h>

typedef NSString * ServerApi;

UIKIT_EXTERN ServerApi const ServerApiLogin;
UIKIT_EXTERN ServerApi const ServerApiRegister;
UIKIT_EXTERN ServerApi const ServerApiBannerList;

@interface JXRequester : NSObject

+ (void)postApi:(ServerApi)api params:(NSDictionary *)params completion:(void (^)())completion;

@end

//
//  JXRequester.m
//  
#import "JXRequester.h"

NSString * const ServerHost = @"http://www.baidu.com/";

ServerApi const ServerApiLogin = @"app/ServerApiLogin";
ServerApi const ServerApiRegister = @"app/ServerApiRegister";
ServerApi const ServerApiBannerList = @"app/ServerApiBannerList";

@implementation JXRequester

+ (void)postApi:(ServerApi)api params:(NSDictionary *)params completion:(void (^)())completion {

    NSString *urlString = [NSString stringWithFormat:@"%@%@", ServerHost, api];
}

@end

//
//  ViewController.m
//  
#import "ViewController.h"
#import "JXRequester.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self onLoginButton];
}

#pragma mark - 登录
- (void)onLoginButton {
    NSDictionary *parms = @{@"username" : @"jiongxing",
                            @"password" : @"123456"};
    [JXRequester postApi:ServerApiLogin params:parms completion:^{
        
    }];
}

若有更好思路欢迎留言 ^^