I would like to add some more suggestions based on my most recent implementation. I ve looked at some code from Apple and I think my code behaves in much the same way.

上述职位已经解释了如何制造NSError物体并归还这些物体,因此我与这一部分赢得了双手。 我只是试图建议一种很好的方法,将错误(代码、电文)纳入你自己的手里。

我建议设立1名负责人,以概述贵领域的所有错误(即:评估、图书馆等)。 我的现任领导人希望:

<>strong>FSError.h

FOUNDATION_EXPORT NSString *const FSMyAppErrorDomain;

enum {
    FSUserNotLoggedInError = 1000,
    FSUserLogoutFailedError,
    FSProfileParsingFailedError,
    FSProfileBadLoginError,
    FSFNIDParsingFailedError,
};

<>strong>FSError.m

#import "FSError.h" 

NSString *const FSMyAppErrorDomain = @"com.felis.myapp";

现在,在将上述数值用于错误时, Apple将给你带来一些基本的标准错误信息。 可产生以下错误:

+ (FSProfileInfo *)profileInfoWithData:(NSData *)data error:(NSError **)error
{
    FSProfileInfo *profileInfo = [[FSProfileInfo alloc] init];
    if (profileInfo)
    {
        /* ... lots of parsing code here ... */

        if (profileInfo.username == nil)
        {
            *error = [NSError errorWithDomain:FSMyAppErrorDomain code:FSProfileParsingFailedError userInfo:nil];            
            return nil;
        }
    }
    return profileInfo;
}

以上代码的标准 Apple生成错误信息(eror. localizedDescription)将考虑如下:

<编码> Error territorial=com.felis.myapp Code=1002 “行动无法完成。 (com.felis.myapp, 1002.)

以上所述对于开发商已经非常有益,因为电文显示发生错误的领域和相应的错误代码。 终端用户将不包含什么错误代码1002<>>>/code>,但我们现在需要为每种代码执行某些冰层信息。

"1000" = "User not logged in.";
"1001" = "Logout failed.";
"1002" = "Parser failed.";
"1003" = "Incorrect username or password.";
"1004" = "Failed to parse FNID."

// error handling ...

#define FS_ERROR_KEY(code)                    [NSString stringWithFormat:@"%d", code]
#define FS_ERROR_LOCALIZED_DESCRIPTION(code)  NSLocalizedStringFromTable(FS_ERROR_KEY(code), @"FSError", nil)

UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" 
            message:FS_ERROR_LOCALIZED_DESCRIPTION(error.code) 
            delegate:nil 
            cancelButtonTitle:@"OK" 
            otherButtonTitles:nil];
[alert show];

我尝试总结一下Alex和jlmendezbonini要点的伟大答案,并添加一项修改,使ARC的所有内容都一致(远非因为ARC会抱怨,因为你应当返回<条码>id,这意味着“任何物体”,但BOOL不是物体类型)。

- (BOOL) endWorldHunger:(id)largeAmountsOfMonies error:(NSError**)error {
    // begin feeding the world s children...
    // it s all going well until....
    if (ohNoImOutOfMonies) {
        // sad, we can t solve world hunger, but we can let people know what went wrong!
        // init dictionary to be used to populate error object
        NSMutableDictionary* details = [NSMutableDictionary dictionary];
        [details setValue:@"ran out of money" forKey:NSLocalizedDescriptionKey];
        // populate the error object with the details
        if (error != NULL) {
             // populate the error object with the details
             *error = [NSError errorWithDomain:@"world" code:200 userInfo:details];
        }
        // we couldn t feed the world s children...return nil..sniffle...sniffle
        return NO;
    }
    // wohoo! We fed the world s children. The world is now in lots of debt. But who cares? 
    return YES;
}

现在,我们不核对我们方法电话的回报价值,而是检查<代码>err是否仍为nil。 否则,我们就有一个问题。

// initialize NSError object
NSError* error = nil;
// try to feed the world
BOOL success = [self endWorldHunger:smallAmountsOfMonies error:&error];
if (!success) {
   // inspect error
   NSLog(@"%@", [error localizedDescription]);
}
// otherwise the world has been fed. Wow, your code must rock.

我所看到的另一个设计模式涉及使用区块,在使用方法时,这种区块特别有用。

我们有以下错误代码:

typedef NS_ENUM(NSInteger, MyErrorCodes) {
    MyErrorCodesEmptyString = 500,
    MyErrorCodesInvalidURL,
    MyErrorCodesUnableToReachHost,
};

您将界定你可产生类似错误的方法:

- (void)getContentsOfURL:(NSString *)path success:(void(^)(NSString *html))success failure:(void(^)(NSError *error))failure {
    if (path.length == 0) {
        if (failure) {
            failure([NSError errorWithDomain:@"com.example" code:MyErrorCodesEmptyString userInfo:nil]);
        }
        return;
    }

    NSString *htmlContents = @"";

    // Exercise for the reader: get the contents at that URL or raise another error.

    if (success) {
        success(htmlContents);
    }
}

那么,当你打电话时,你就不必担心宣布NSError物体(完成编码会给你),或检查返回价值。 你们只能提供两块:一是例外,一是例外,一是当它成功时,就会有人要求:

[self getContentsOfURL:@"http://google.com" success:^(NSString *html) {
    NSLog(@"Contents: %@", html);
} failure:^(NSError *error) {
    NSLog(@"Failed to get contents: %@", error);
    if (error.code == MyErrorCodesEmptyString) { // make sure to check the domain too
        NSLog(@"You must provide a non-empty string");
    }
}];

extension NSError {
    static func defaultError() -> NSError {
        return NSError(domain: "com.app.error.domain", code: 0, userInfo: [NSLocalizedDescriptionKey: "Something went wrong."])
    }
}

当我没有有效的错误反对时,我可以使用<代码>NSError.defaultError(。

let error = NSError.defaultError()
print(error.localizedDescription) //Something went wrong.

Well it s a little bit out of question scope but in case you don t have an option for NSError you can always display the Low level error:

 NSLog(@"Error = %@ ",[NSString stringWithUTF8String:strerror(errno)]);