Bool method to check user input - nsexception

Question

Hi everybody i am trying to make a boolean method that will return value depending upon the user input for the field when submit button is clicked.
- (BOOL)checkuser:(NSString*)input
{
bool result = NO;
if ([input isEqualToString:#"test"])
{
result = YES;
}
else
{
result = NO;
}
return result;
}
And i am refrencing this method from my program as
else if ([Username checkuser] == YES)
{ // do something
}
with following warning
'NSString' may not respond to '-checkuser'
and i am not getting why my program crashing at this point with following error.
2011-03-22 22:57:25.942 Assignment 2[824:207] -[NSCFString checkuser]: unrecognized selector sent to instance 0x4b7c050
2011-03-22 22:57:25.944 Assignment 2[824:207] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSCFString checkuser]: unrecognized selector sent to instance 0x4b7c050'
* Call stack at first throw:
(
0 CoreFoundation 0x00db8be9 exceptionPreprocess + 185
1 libobjc.A.dylib 0x00f0d5c2 objc_exception_throw + 47
2 CoreFoundation 0x00dba6fb -[NSObject(NSObject) doesNotRecognizeSelector:] + 187
3 CoreFoundation 0x00d2a366 __forwarding + 966
4 CoreFoundation 0x00d29f22 _CF_forwarding_prep_0 + 50
5 Assignment 2 0x00002958 -[Assignment_2ViewController SubmitbuttonPressed:] + 727
6 UIKit 0x002c1a6e -[UIApplication sendAction:to:from:forEvent:] + 119
7 UIKit 0x003501b5 -[UIControl sendAction:to:forEvent:] + 67
8 UIKit 0x00352647 -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 527
9 UIKit 0x003511f4 -[UIControl touchesEnded:withEvent:] + 458
10 UIKit 0x002e60d1 -[UIWindow _sendTouchesForEvent:] + 567
11 UIKit 0x002c737a -[UIApplication sendEvent:] + 447
12 UIKit 0x002cc732 _UIApplicationHandleEvent + 7576
13 GraphicsServices 0x016eea36 PurpleEventCallback + 1550
14 CoreFoundation 0x00d9a064 CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION + 52
15 CoreFoundation 0x00cfa6f7 __CFRunLoopDoSource1 + 215
16 CoreFoundation 0x00cf7983 __CFRunLoopRun + 979
17 CoreFoundation 0x00cf7240 CFRunLoopRunSpecific + 208
18 CoreFoundation 0x00cf7161 CFRunLoopRunInMode + 97
19 GraphicsServices 0x016ed268 GSEventRunModal + 217
20 GraphicsServices 0x016ed32d GSEventRun + 115
21 UIKit 0x002d042e UIApplicationMain + 1160
22 Assignment 2 0x00001c04 main + 102
23 Assignment 2 0x00001b95 start + 53
)
terminate called after throwing an instance of 'NSException'
Program received signal: “SIGABRT”.
(gdb)

Answer 1

You're over-complicating a very simple problem:
- (BOOL) checkuser:(NSString*)input {
return [input isEqualToString:#"test"];
}
and then to call it:
if ([Username checkUser:#"DONT FORGET YOUR PARAM HERE"]) {
// Do something...
}
In your example, you're not passing any parameter to your method... That's a misstake hence your error.
Also, if you create a method returning a 'BOOL', make sure you're returning a 'BOOL' and not a 'bool'. You have to always keep in mind that the underlying types can be different, even if a bool can be evaluated to a BOOL.

Answer 2

else if ([Username checkuser] == YES)
checkuser is supposed to receive a NSString*, which you are not sending though and is the reason for error messages. So, it should be -
Assuming someNSString is initialized and is of type NSString*.
else if( ([Username checkuser:someNSString] ) == YES )
// ^^^^^^^^^^^^ Needs to be passed as the method prototype mentions so.
{
// ....
}
NSString* someNSString = #"Forgot to pass this" ;
else if( ([Username checkuser:someNSString] ) == YES )
// ^^^^^^^^^^^^ Needs to be passed as the method prototype mentions so.
{
// ....
}