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Objective C Error Domains


The method extracts the localized information from the passed-in NSError object for its message text, informative text, and button titles. When the file loads successfully, the method returns the contents of the file as an NSString, but when it fails, it directly returns nil and indirectly returns the error by populating Notice this error object gets a nil for its support dictionary. The NSError Class The one thing that errors and exceptions have in common is that they are both implemented as objects. http://brecnc.org/objective-c/objective-c-catch-error.html

And the accessor userInfo returns the support dictionary as an NSDictionary object. This is only used by clients that want to isolate the reason for the error from its full description. The following snippet demonstrates this error-handling pattern by trying to load a file that doesn’t exist via NSString’s stringWithContentsOfFile:encoding:error: method. Typically, you'll want to define constants for custom error domains and codes so that they are consistent across classes.

Nserror Domain Swift

You can also approach the distinction between exceptions and errors as a difference in their target audiences. Dobb's Journal November - Mobile Development August - Web Development May - Testing February - Languages Dr. Find the maximum deviation What causes a 20% difference in fuel economy between winter and summer Asking for a written form filled in ALL CAPS What game is this picture showing

It's very important to check that the user actually passed a valid **error parameter with if (error != NULL). The following example demonstrates a realistic use case for NSError. And this alteration of the function prototype is the result of automatic bridging, as described in Apple’s “Using Swift with Cocoa and Objective-C”: Swift automatically bridges between the Error type and Cocoa Error Codes But again, a simple if-statement would be preferred.

There are times when you want the domain to be unique, I would assume ... Nserror Code List However, if you change the interval to something like (0, -10), you'll get to see the @catch() block in action. This varies based on the type of error. The example shows you how @throw can work with different types of objects, but strictly speaking, this isn't the best application design, nor is it the most efficient use of Objective-C's

Its main properties are similar to NSException. Custom Nserror Swift We introduce you to Apple's new Swift programming language, discuss the perils of being the third-most-popular mobile platform, revisit SQLite on Android , and much more! This information is usually stored in the user info dictionary as strings in several categories: description, failure reason, recovery suggestion, and recovery options. (See Figure 1-1 for the placement of these Browse PHP on CodeCanyonFollow Envato Tuts+© 2016 Envato Pty Ltd.

Nserror Code List

Creating a custom error domain and set of error codes could significantly disambiguate your code, but is it too much overhead to maintain and does one have to worry about error The Error Object The NSError class (Figure 1) serves as the basis for an error object. Nserror Domain Swift Also note how we defined localizedDescription by manually adding it to the userInfo dictionary with NSLocalizedDescriptionKey. // main.m #import #import "InventoryErrors.h" NSString *getRandomCarFromInventory(NSArray *inventory, NSError **error) { int maximum = Nserror Example In it, you'll get: The week's top questions and answers Important community announcements Questions that need answers see an example newsletter By subscribing, you agree to the privacy policy and terms

Because errors are expected during the normal execution of a program, you should manually check for these kinds of conditions and inform the user when they occur. weblink An error object has an error description of “File could not be saved because the disk is full.” The accompanying failure reason is “The disk is full.”Recovery suggestionA secondary sentence that The NSError class encapsulates the details surrounding a failed operation. When an exception is encountered in the @try block, the program jumps to the corresponding @catch() block, which means any code after the exception occurred won't be executed. Nscocoaerrordomain Codes

The easiest way to create an NSException instance is through the exceptionWithName:reason:userInfo: factory method. This is usually a signed integer (NSInteger). Example NSError *error = [[NSError alloc] initWithDomain:@"com.eezytutorials.iosTuts" code:200 userInfo:@{ NSLocalizedFailureReasonErrorKey:@"LocalizedFailureReason", NSLocalizedDescriptionKey:@"LocalizedDescription", NSLocalizedRecoverySuggestionErrorKey:@"LocalizedRecoverySuggestion", NSLocalizedRecoveryOptionsErrorKey:@"LocalizedRecoveryOptions", NSRecoveryAttempterErrorKey:@"RecoveryAttempter", NSHelpAnchorErrorKey:@"HelpAnchor", NSStringEncodingErrorKey:@"NSStringEncodingError", NSURLErrorKey:@"NSURLError", NSFilePathErrorKey:@" NSFilePathError" }]; NSLog(@"%@",[error localizedRecoveryOptions]); Output 2014-04-12 05:40:40.918 iOS-Tutorial[1638:a0b] LocalizedRecoveryOptions - localizedRecoverySuggestion Returns a navigate here Aborting a program due to an uncaught exception Next, we'll learn how to catch exceptions and prevent the program from terminating.

These are used in the next section’s example. Nsunderlyingerrorkey Personally, I usually just pass on framework-generated errors as they came to me, since I'm never quite sure that I'll handle all the codes and translate all of the userInfo into They are designed to inform the developer that an unexpected condition occurred.

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These strings can be used to check what type of exception was caught. When the above code is compiled and executed, it produces the following result: 2013-09-14 18:01:00.809 demo[27632] Name1: Employee Test Name 2013-09-14 18:01:00.809 demo[27632] Error finding Name2: Unable to complete the process After that, you’ll probably want to figure out what went wrong by inspecting the NSError or NSException object so that you can try to recover from it. Error Handling In Objective C Dobb's moderates all comments posted to our site, and reserves the right to modify or remove any content that it determines to be derogatory, offensive, inflammatory, vulgar, irrelevant/off-topic, racist or obvious

This varies based on the type of exception. Example NSError *error = [[NSError alloc] initWithDomain:@"com.eezytutorials.iosTuts" code:200 userInfo:@{ NSLocalizedFailureReasonErrorKey:@"LocalizedFailureReason" }]; NSLog(@"%d",[error code]); Output 2014-04-12 05:42:56.399 iOS-Tutorial[1699:a0b] 200 - domain Returns the receiver’s error domain. The @finally block solves this problem, since it is guaranteed to be executed regardless of whether an exception occurred. his comment is here If the file exists, the snippet runs the desired file operation.

You may also like: Recursive Tail Calls and Trampolines in Swift May 2016 Swift And C: Everything You Need to Know Apr 2016 A Recap of the Swift Porting Efforts #2 Here are some interesting findings discussed throughout the blog post: Objective-C methods can only be translated to Swift’s error handling mechanism if they return Objective-C objects or boolean values Swift will All of these are actually shortcuts into the userInfo dictionary described in the previous list. There are three principal steps to the process. 1.

Error Domains An error domain is like a namespace for error codes. Note that the localizedDescription and localizedFailureReason methods are an alternative way to access the first two keys, respectively. It also helps me more specifically identify where the error came from. The three properties that constitute an exception are described as follows: name - An instance of NSString that uniquely identifies the exception.

It creates an instance of the Cocoa class NSFileManager (line 9) and declares the path to the file "Foo.text" (lines 10-11). Do TRS connectors short adjacent contacts during insertion? Listing Two #import . . . Throwing Exceptions When you detect an exceptional condition in your code, you create an instance of NSException and populate it with the relevant information.

Then, you throw it using the aptly named @throw directive, prompting the nearest @try/@catch block to handle it. This means being able to encapsulate an error as it occurs, to dispatch it, and to respond to it properly. Caught exception: %@", [exception name]); } NSLog(@"Random Number: %i", result); } return 0; } Instead of throwing an NSException object, generateRandomInteger() tries to generate a new number between some "default" bounds. userInfo - An instance of NSDictionary that contains application-specific information related to the error.

As you can see, a function doesn't typically return an NSError object-it returns whatever value it's supposed to if it succeeds, otherwise it returns nil. It can carry a collection of localized strings needed to describe the error. User Info: The userInfo dictionary for the error and userInfo may be nil. That was pretty surprising, given that the protocol definition for ErrorType in Xcode looks like this: protocol ErrorType { } Hidden Protocol Requirements The error message revealed two hidden protocol requirements:

The @try, @catch(), and @finally compiler directives are used to catch and handle exceptions, and the @throw directive is used to detect them.