Getting isEqualToString: unrecognized selector sent to instance error - iphone

Question

I'm getting this error when clicking the same UIButton twice, it crashes the second time only when the request to the server is not able to go through.
-[SendHelloFax isEqualToString:]: unrecognized selector sent to instance 0x12b49150
Update: I used breakpoints and found that the line it is crashing at is:
if (!errorMessage || [errorMessage isEqualToString:#""])
{
errorMessage = #"Failed to send fax. Please check your WiFi or 3G connection and try again.";
}
Methods:
- (IBAction)sendFaxButtonClicked:(id)sender
{
NSString *errorMessage;
int rcode = [MyDataSource sendFax:self.appointment phone_call_id:self.phone_call_id document_url:self.document_url targetId:self.contact_id targetName:self.name.text targetNumber:self.faxNumber.text coverSheetMessage:self.coverSheetMessage.text errorMessage:&errorMessage];
if (rcode) {
if (!errorMessage || [errorMessage isEqualToString:#""]) {
errorMessage = #"Failed to send fax. Please check your WiFi or 3G connection and try again.";
}
UIAlertView *someError = [[UIAlertView alloc] initWithTitle: #"Error" message:errorMessage delegate: self cancelButtonTitle: #"Ok" otherButtonTitles: nil];
[someError show];
[someError release];
return;
}
if (!rcode) {
[self dismissModalViewControllerAnimated:FALSE];
}
}
+(int)sendFax:(int)appointment_id phone_call_id:(int)phone_call_id document_url:(NSString*)document_url targetId:(int)contactId targetName:(NSString*)targetName targetNumber:(NSString*)targetNumber coverSheetMessage:(NSString*)coverSheetMessage errorMessage:(NSString**)errorMessage
{
NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:#"%#/ichrono/20110715/60b88126/fax_send/", [self getMyHost]]];
ASIFormDataRequest *request = [[[ASIFormDataRequest alloc] initWithURL:url] autorelease];
[self addCurrentUserLoginToPostRequest:request];
[request setPostValue:[NSString stringWithFormat:#"%d", contactId] forKey:#"fax_contact_id"];
[request setPostValue:[NSString stringWithFormat:#"%d", appointment_id] forKey:#"appointment_id"];
[request setPostValue:[NSString stringWithFormat:#"%d", phone_call_id] forKey:#"phone_call_id"];
[request setPostValue:document_url forKey:#"url_to_fax"];
[request setPostValue:targetNumber forKey:#"fax_number"];
[request setPostValue:targetName forKey:#"full_name"];
[request setPostValue:coverSheetMessage forKey:#"coversheet_message"];
[request startSynchronous];
NSError *error = [request error];
NSString *responseString;
if (!error) {
responseString = [request responseString];
} else {
return -1;
}
NSMutableDictionary *temp = [responseString JSONValue];
*errorMessage = [temp valueForKey:#"errors"];
if ([[temp valueForKey:#"status"] isEqualToString:#"ok"]) {
return 0;
} else {
return -1;
}
}

Answer 1

Best bet is that errorMessage is not initialized and not set to a NSString even though rcode is not 0.
Try: NSString *errorMessage - nil; and checking to insure errorMessage is set in this instance.

Answer 2

When, at the beginning of your method, you define - without initialization -:
NSString *errorMessage;
you're in fact defining an id which has not been set to a valid value (that is a valid string using alloc-init or simply nil) so the memory area content pointed by errorMessage is not valid, that is it can be anything: an invalid area (which will lead to EXC_BAD_ACCESS) or another area previously taken by a now dealloc'd class (like in your case: this will raise an invalid selector exception) or in the worst case an area taken by another now dealloc'd NSString (difficult to debug!).
Later you call sendFax:phone_call_id:... method which returns rcode and has as side effect to update the errorMessage pointer by let it point to a valid address (or nil). It doesn't and then when you check errorMessage you get one of the errors above.
I suppose from your code that when rcode is set some error occurred. In such case this method must assign something to errorMessage, even a nil or an empty string, to avoid this error. So probably the sendFax: method is missing this detail.