Objective-C Fundamentals

Creating NSError objects
209
10.2.2 Handling and displaying RentalManagerAPI errors
Let’s look at listing 10.5. What does this code do? First it prepares the ad dictionary
from the values of some text fields. Then it declares a pointer of type NSError and
calls the publishAd:error: method, checking its return value. If it’s YES, a success
message is displayed. If it’s NO (which indicates an error), you check if the error
domain is that of the RentalManagerAPI. If so, you check for different error codes and
construct an appropriate message. Otherwise, you just use the localizedDescription
and finally display it in a UIAlertView. That’s it.
Listing 10.5
Calling the publishAd:error: method
- (IBAction)publishAd:(id)sender {
NSArray *keys = [NSArray arrayWithObjects:@"name", @"city",
@"price", nil];
NSArray *values = [NSArray arrayWithObjects:nameTextField.text,
cityTextField.text,
priceTextField.text, nil];
NSDictionary *ad = [NSDictionary dictionaryWithObjects:values
forKeys:keys];
NSError *error;
if ([RentalManagerAPI publishAd:ad error:&error]) {
UIAlertView *av = [[UIAlertView alloc]
initWithTitle:@"Success"
message:@"Ad published successfully."
delegate:nil
cancelButtonTitle:@"OK"
otherButtonTitles:nil];
[av show];
[av release];
} else {
NSString *message;
Create NSError pointer
if ([error domain] == RMAErrorDomain) {
switch ([error code]) {
case RMAValidationError:
message = [NSString
Create
the “ad”
stringWithFormat:@"%@\nMissing values: %@.",
[error localizedDescription],
[[[error userInfo] objectForKey:
RMAMissingValuesKey]
componentsJoinedByString:@", "]];
break;
case RMAWrongCredentialsError:
break;
default:
message = [error localizedDescription];
break;
}
} else {
message = [error localizedDescription];
}
On success,
display message
Handle errors
differently
Call
RentalManagerAPI
Custom error
domain only
Messages for
validation
errors
Other errors, use
its message