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 have a 2.67 GHz Celeron processor, 1.21 GB of RAM on a x86 Windows XP Professional machine. My understanding is that the Android emulator should start fairly quickly on such a machine, but for me it does not. I have followed all instructions in setting up the IDE, SDKs, JDKs and such and have had some success in staring the emulator quickly but is very particulary. How can I, if possible, fix this problem?
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.
ReplyDeleteExample:
- (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.
Great answer Alex. One potential issue is the NULL dereference. Apple's reference on Creating and Returning NSError objects
ReplyDelete...
[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;
...
Please refer following tutorial
ReplyDeletei hope it will helpful for you but prior you have to read documentation of NSError