How can I use NSError in my iPhone App?
我正在努力捕获应用程序中的错误,并且正在考虑使用
有人可以提供一个示例说明我如何填充然后使用
好吧,我通常要做的是使我的方法在运行时可能出错,并引用
例:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | - (id) 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 *error = [NSError errorWithDomain:@"world" code:200 userInfo:details]; // we couldn't feed the world's children...return nil..sniffle...sniffle return nil; } // wohoo! We fed the world's children. The world is now in lots of debt. But who cares? return YES; } |
然后我们可以使用这种方法。除非该方法返回nil,否则甚至不必费心检查错误对象:
1 2 3 4 5 6 7 8 9 | // initialize NSError object NSError* error = nil; // try to feed the world id yayOrNay = [self endWorldHunger:smallAmountsOfMonies error:&error]; if (!yayOrNay) { // inspect error NSLog(@"%@", [error localizedDescription]); } // otherwise the world has been fed. Wow, your code must rock. |
我们能够访问错误的
有关更多信息的最佳位置是Apple的文档。真的很好。
关于可可粉是我的女朋友,还有一个很好的简单教程。
我想根据我的最新实现添加更多建议。我看过苹果公司的一些代码,我认为我的代码行为大致相同。
上面的帖子已经解释了如何创建NSError对象并返回它们,因此我不会理会该部分。我将尝试建议一种在您自己的应用程序中集成错误(代码,消息)的好方法。
我建议创建1个标头,该标头将概述您域中的所有错误(即应用程序,库等)。我当前的标题如下:
FSError.h
1 2 3 4 5 6 7 8 9 | FOUNDATION_EXPORT NSString *const FSMyAppErrorDomain; enum { FSUserNotLoggedInError = 1000, FSUserLogoutFailedError, FSProfileParsingFailedError, FSProfileBadLoginError, FSFNIDParsingFailedError, }; |
FSError.m
1 2 3 | #import"FSError.h" NSString *const FSMyAppErrorDomain = @"com.felis.myapp"; |
现在,当使用上述错误值时,Apple将为您的应用创建一些基本的标准错误消息。可能会产生如下错误:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | + (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; } |
苹果公司为上述代码生成的标准错误消息(
上面的内容对于开发人员已经非常有用,因为该消息显示了发生错误的域和相应的错误代码。最终用户将不知道错误代码
对于错误消息,我们必须牢记本地化(即使我们没有立即实施本地化的消息)。我在当前项目中使用了以下方法:
1)创建一个将包含错误的
FSError.strings
1 2 3 4 5 | "1000" ="User not logged in."; "1001" ="Logout failed."; "1002" ="Parser failed."; "1003" ="Incorrect username or password."; "1004" ="Failed to parse FNID." |
2)添加宏以将整数代码转换为本地化的错误消息。我在Constants + Macros.h文件中使用了2个宏。为了方便起见,我总是将此文件包含在前缀标头(
常数+ Macros.h
1 2 3 4 | // error handling ... #define FS_ERROR_KEY(code) [NSString stringWithFormat:@"%d", code] #define FS_ERROR_LOCALIZED_DESCRIPTION(code) NSLocalizedStringFromTable(FS_ERROR_KEY(code), @"FSError", nil) |
3)现在很容易显示基于错误代码的用户友好错误消息。一个例子:
1 2 3 4 5 6 | UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:FS_ERROR_LOCALIZED_DESCRIPTION(error.code) delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil]; [alert show]; |
很好的答案,Alex。一个潜在的问题是NULL取消引用。 Apple关于创建和返回NSError对象的参考
1 2 3 4 5 6 7 8 9 10 | ... [details setValue:@"ran out of money" forKey:NSLocalizedDescriptionKey]; 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 nil; ... |
目标C
1 2 3 4 5 | NSError *err = [NSError errorWithDomain:@"some_domain" code:100 userInfo:@{ NSLocalizedDescriptionKey:@"Something went wrong" }]; |
迅捷3
1 2 3 | let error = NSError(domain:"some_domain", code: 100, userInfo: [NSLocalizedDescriptionKey:"Something went wrong"]) |
请参考以下教程
我希望它对您有帮助,但是在您必须阅读NSError文档之前
这是我最近发现的非常有趣的链接ErrorHandling
我见过的另一种设计模式涉及使用块,这在异步运行方法时特别有用。
假设我们定义了以下错误代码:
1 2 3 4 5 | typedef NS_ENUM(NSInteger, MyErrorCodes) { MyErrorCodesEmptyString = 500, MyErrorCodesInvalidURL, MyErrorCodesUnableToReachHost, }; |
您将定义可能引发如下错误的方法:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | - (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); } } |
然后,当您调用它时,您不必担心声明NSError对象(代码完成将为您完成)或检查返回值。您可以只提供两个块:一个在发生异常时将被调用,而另一个在成功时将被调用:
1 2 3 4 5 6 7 8 | [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"); } }]; |
我将尝试总结一下Alex和jlmendezbonini的观点的很好的答案,并添加一个修改内容,使所有ARC都兼容(到目前为止,这不是因为ARC会抱怨,因为您应该返回
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | - (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,我们检查
1 2 3 4 5 6 7 8 9 | // 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. |
好吧,这超出了问题范围,但是如果您没有NSError选项,则可以始终显示低级错误:
1 |