I have a method which take the parameter
(void(^)(NSError*))errorCall;
I need to pass errorCall value
-(void)message{
example = [[Example alloc]init]
[example opertationError:void(^)(NSError*))errorCall ];
}
for the below line
[example opertationError:void(^)(NSError*))errorCall];
i need to pass some custom error call which in type of void(^)(NSError*))errorCall
Please any one let me know how to pass this kind of error value to the method.
#All
Thanks in advance
You can do like this:
void(^aBlock)(NSError *) = ^(NSError *error) {
...
};
[self errorValue:aBlock];
Related
I want to mock the facebook login block, but test failed, the block wasn't invoked. Please help me solve the problem.
//Test
-(void)testFacebookLogin
{
id mockManager = OCMClassMock([FBSDKLoginManager class]);
OCMStub([[mockManager alloc]init]).andReturn(mockManager);
FBSDKLoginManagerLoginResult *res = [[FBSDKLoginManagerLoginResult alloc]initWithToken:nil isCancelled:YES grantedPermissions:nil declinedPermissions:nil];
NSError* err = [NSError errorWithDomain:#"This is an error" code:NSURLErrorNotConnectedToInternet userInfo:nil];
[[mockManager stub]logInWithReadPermissions:OCMOCK_ANY fromViewController:OCMOCK_ANY handler:[OCMArg invokeBlockWithArgs:res,err,nil]];
__block BOOL invoke;
[LoginHelper facebookLoginWithLoginResult:^(BOOL success, NSError *error, id result) {
invoke = YES;
}];
XCTAssertTrue(invoke);
}
//LoginHelper.m
+(void)facebookLoginWithLoginResult:(LoginResult)loginResult
{
UIViewController* currentRootViewController = AppDelegateHelperSingleton.globalDelegate.window.rootViewController;
FBSDKLoginManager* loginManager = [[FBSDKLoginManager alloc]init];
loginManager.loginBehavior = FBSDKLoginBehaviorNative;
NSArray* permissions = #[#"email",#"public_profile",#"user_birthday"];
//facebook login with read permisssions
[loginManager logInWithReadPermissions:permissions fromViewController:currentRootViewController handler:^(FBSDKLoginManagerLoginResult *result, NSError *error)
{
loginResult(result, error);
}];
}
OCMStub([[mockManager alloc]init]).andReturn(mockManager);
That's not going to work. The problem you face is that your production code has a dependency which it locks down:
FBSDKLoginManager* loginManager = [[FBSDKLoginManager alloc]init];
In order for your test code to supply a "test double" (something that stands in for the real thing), you need a way to inject it.
There are various approaches to Dependency Injection. You can make it an initializer argument. You can make it a property. If you want the FBSDKLoginManager to be short-lived, you can make it a method argument.
For more, see How to Use Dependency Injection to Make Your Code Testable
I have a singleton that I'm using to parse XML and then cache it. The parsing/caching is done with a block. Is there any way for me to pass an argument to this block from another class so that I can change the URL from outside the singleton?
Here's the code I have now:
// The singleton
+ (FeedStore *)sharedStore
{
static FeedStore *feedStore = nil;
if(!feedStore)
feedStore = [[FeedStore alloc] init];
return feedStore;
}
- (RSSChannel *)fetchRSSFeedWithCompletion:(void (^)(RSSChannel *obj, NSError *err))block
{
NSURL *url = [NSURL URLWithString:#"http://www.test.com/test.xml"];
...
return cachedChannel;
}
And here's the class where I need to modify the NSURL from:
- (void)fetchEntries
{
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
// Initiate the request...
channel = [[BNRFeedStore sharedStore] fetchRSSFeedWithCompletion:
^(RSSChannel *obj, NSError *err) {
...
}
}
How do I pass an argument from fetchEntries to fetchRSSFeedWithCompletion?
You would want to add a parameter in the method, not the block.
Also, when using a completion block, there really is no reason to return anything in the method.
I'd change it to look like this:
-(void)fetchRSSFeed:(NSURL *)rssURL completion:(void (^)(RSSChannel *obj, NSError *error))block{
RSSChannel *cachedChannel = nil;
NSError *error = nil;
// Do the xml work that either gets you a RSSChannel or an error
// run the completion block at the end rather than returning anything
completion(cachedChannel, error);
}
why is "error:&error" used here (objective-c)
NSError *error = nil;
NSArray *array = [moc executeFetchRequest:request error:&error];
wouldn't an object in objective-c be effectively pass-by-reference anyway?
The argument type for error: is NSError** (i.e. a pointer to a pointer to an object). This permits the moc object to allocate and initialize a new NSError object as required. It is a common pattern, especially in Cocoa.
The NSError documentation gives some indication of the motivation for this approach:
Applications may choose to create subclasses of NSError to provide better localized error strings by overriding localizedDescription.
Passing in an NSError** argument allows that method to return any subclass of NSError that makes sense. If you passed in NSError*, you would have to supply an existing NSError object, and there would be no way for the method to return a different object from the one you passed in.
To be clear, the method could look something like this:
- (NSArray*)executeFetchRequest:(Request *)request error:(NSError**)error {
...
if ((error != NULL) && (some_error_condition)) {
*error = [[[SomeNSErrorSubclass alloc] init...] autorelease];
return nil;
}
}
Note that this also allows the calling code to ignore errors by simply passing in NULL for the error: parameter, as follows:
NSArray *array = [moc executeFetchRequest:request error:NULL];
Update: (in response to questions):
There are two reasons why the argument type has to be NSError** instead of NSError*: 1. variable scoping rules, and 2. NSError instances are imutable.
Reason #1: variable scoping rules
Let's assume that the function declaration were to look like this:
- (NSArray*)executeFetchRequest:(Request *)request error:(NSError*)error;
And we were to call the function like this:
NSError * error = nil;
[someArray executeFetchRequest:someRequest error:error];
if (error != nil) { /* handle error */ }
When you pass in a variable this way, the function body will not be able to modify the value of that variable (i.e. the function body will not be able to create a new variable to replace the existing one). For example, the following variable assignments will exist only in the local scope of the function. The calling code will still see error == nil.
- (NSArray*)executeFetchRequest:(Request *)request error:(NSError*)error {
...
error = [[[NSError alloc] init...] autorelease]; // local only
error = [[[SomeNSErrorSubclass alloc] init...] autorelease]; // local only
}
Reason #2: instances of NSError are immutable
Let's keep the same function declaration, but call the function like this:
NSError * error = [[[NSError alloc] init...] autorelease];
[someArray executeFetchRequest:someRequest error:error];
if (error != nil) { /* handle error */ }
First of all, the variable scoping rules guarantee that error can not be nil, so the if (error != nil) { ... condition will always be true, but even if you wanted to check for specific error information inside the if block, you would be out of luck because instances of NSError are immutable. This means that once they are created, you cannot modify their properties, so the function would not be able to change the domain or userInfo of that NSError instance that you created in the calling code.
- (NSArray*)executeFetchRequest:(Request *)request error:(NSError*)error {
...
error.domain = ... // not allowed!
error.userInfo = ... // not allowed!
}
It's effectively another return value. The error is not dominant by convention in Cocoa when there is a return value for the operation. When an error is encountered, it may be returned to you by this out parameter.
In the case of NSError, it works this way because NSError is not a mutable type - its fields are set at initialization and never mutated. Therefore, you cannot pass an NSError as usual and set the error code.
I am working on catching errors in my app, and I am looking into using NSError. I am slightly confused about how to use it, and how to populate it.
Could someone provide an example on how I populate then use NSError?
Well, what I usually do is have my methods that could error-out at runtime take a reference to a NSError pointer. If something does indeed go wrong in that method, I can populate the NSError reference with error data and return nil from the method.
Example:
- (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;
}
We can then use the method like this. Don't even bother to inspect the error object unless the method returns nil:
// 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.
We were able to access the error's localizedDescription because we set a value for NSLocalizedDescriptionKey.
The best place for more information is Apple's documentation. It really is good.
There is also a nice, simple tutorial on Cocoa Is My Girlfriend.
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.
The posts above already explain how to create NSError objects and return them, so I won't bother with that part. I'll just try to suggest a good way to integrate errors (codes, messages) in your own app.
I recommend creating 1 header that will be an overview of all the errors of your domain (i.e. app, library, etc..). My current header looks like this:
FSError.h
FOUNDATION_EXPORT NSString *const FSMyAppErrorDomain;
enum {
FSUserNotLoggedInError = 1000,
FSUserLogoutFailedError,
FSProfileParsingFailedError,
FSProfileBadLoginError,
FSFNIDParsingFailedError,
};
FSError.m
#import "FSError.h"
NSString *const FSMyAppErrorDomain = #"com.felis.myapp";
Now when using the above values for errors, Apple will create some basic standard error message for your app. An error could be created like the following:
+ (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;
}
The standard Apple-generated error message (error.localizedDescription) for the above code will look like the following:
Error Domain=com.felis.myapp Code=1002 "The operation couldn’t be completed. (com.felis.myapp error 1002.)"
The above is already quite helpful for a developer, since the message displays the domain where the error occured and the corresponding error code. End users will have no clue what error code 1002 means though, so now we need to implement some nice messages for each code.
For the error messages we have to keep localisation in mind (even if we don't implement localized messages right away). I've used the following approach in my current project:
1) create a strings file that will contain the errors. Strings files are easily localizable. The file could look like the following:
FSError.strings
"1000" = "User not logged in.";
"1001" = "Logout failed.";
"1002" = "Parser failed.";
"1003" = "Incorrect username or password.";
"1004" = "Failed to parse FNID."
2) Add macros to convert integer codes to localized error messages. I've used 2 macros in my Constants+Macros.h file. I always include this file in the prefix header (MyApp-Prefix.pch) for convenience.
Constants+Macros.h
// 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) Now it's easy to show a user friendly error message based on an error code. An example:
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Error"
message:FS_ERROR_LOCALIZED_DESCRIPTION(error.code)
delegate:nil
cancelButtonTitle:#"OK"
otherButtonTitles:nil];
[alert show];
Great answer Alex. One potential issue is the NULL dereference. Apple's reference on Creating and Returning NSError objects
...
[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;
...
Objective-C
NSError *err = [NSError errorWithDomain:#"some_domain"
code:100
userInfo:#{
NSLocalizedDescriptionKey:#"Something went wrong"
}];
Swift 3
let error = NSError(domain: "some_domain",
code: 100,
userInfo: [NSLocalizedDescriptionKey: "Something went wrong"])
Please refer following tutorial
i hope it will helpful for you but prior you have to read documentation of NSError
This is very interesting link i found recently ErrorHandling
I'll try summarize the great answer by Alex and the jlmendezbonini's point, adding a modification that will make everything ARC compatible (so far it's not since ARC will complain since you should return id, which means "any object", but BOOL is not an object type).
- (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;
}
Now instead of checking for the return value of our method call, we check whether error is still nil. If it's not we have a problem.
// 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.
Another design pattern that I have seen involves using blocks, which is especially useful when a method is being run asynchronously.
Say we have the following error codes defined:
typedef NS_ENUM(NSInteger, MyErrorCodes) {
MyErrorCodesEmptyString = 500,
MyErrorCodesInvalidURL,
MyErrorCodesUnableToReachHost,
};
You would define your method that can raise an error like so:
- (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);
}
}
And then when you call it, you don't need to worry about declaring the NSError object (code completion will do it for you), or checking the returning value. You can just supply two blocks: one that will get called when there is an exception, and one that gets called when it succeeds:
[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."])
}
}
which I can use NSError.defaultError() whenever I don't have valid error object.
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)]);
I have the following method:
- (NSMutableArray *)getElements:(NSString *)theURL;
And I wanted to know if there is a way to call that method using performSelectorOnMainThread so that I can get the return value. So far, I've tried with:
myArray = [object performSelectorOnMainThread:#selector(getElements:)
withObject:url waitUntilDone:YES];
but it doesn't work, since performSelectorOnMainThread returns void. How could I solve this?
Welcome to a multi-threaded environment my friend.
You'll need to store the return value in an instance variable or pass in an object by reference through the withObject parameter:
NSMutableDictionary *myDict;
[object performSelectorOnMainThread:#selector(getElements:)
withObject:&myDict waitUntilDone:YES];
Your method prototype should now look like this:
- (void)getElements:(NSMutableDictionary **)objects;
You can't do it directly, because, as you say, that method returns void.
So, you'd have to arrange another way to get a value back, for example by passing an NSDictionary instead of an NSString, and having the method store the result in the dictionary for you.
Had to implement this recently. Great candidate for adding a category to NSObject so that all your objects can do this:
#implementation NSObject (CallSelectorWithObjectOnMainThread)
- (id)resultFromSelectorOnMainThread:(SEL)selector object:(id)object {
NSMutableDictionary *resultDictionary = [NSMutableDictionary dictionaryWithCapacity:1];
NSMutableDictionary *callDict = [NSMutableDictionary dictionaryWithObjectsAndKeys:resultDictionary, #"ResultDictionary", NSStringFromSelector(selector), #"Selector", nil];
if(object) [callDict setValue:object forKey:#"Object"];
[self performSelectorOnMainThread:#selector(callObject:) withObject:callDict waitUntilDone:YES];
return [resultDictionary objectForKey:#"Result"];
}
- (void)callObject:(NSMutableDictionary *)info {
id result;
SEL selector = NSSelectorFromString([info objectForKey:#"Selector"]);
id object = [info objectForKey:#"Object"];
NSMutableDictionary *resultDictionary = [info objectForKey:#"Dictionary"];
if(object)
result = [self performSelector:selector withObject:object];
else
result = [self performSelector:selector];
if(result)
[resultDictionary setValue:result forKey:#"Result"];
}
#end
I have universal solution for async blocking call with return value for any thread, not only main. This example for main thread like performSelectorOnMainThread:withObject:waitUntilDone:
__block id result = nil;
NSOperationQueue* targetQueue = [NSOperationQueue* mainQueue];
// targetQueue is main thread, but it may be queue on any thread.
[targetQueue addBlockOperation:^{
// performs on target thread.
result = [someObject someSelector];
}];
// wait until operations on targetQueue will finished.
[targetQueue waitUntilAllOperationsAreFinished];
// result is ready here.
I used this technique only in ARC environment.