Restricting what is passed into a method - iphone

Question

Right lets say I have a method something like :
- (void)doStuff:(NSString *)doStuffWith;
Can I make it so that doStuffWith will only accept certain words like lets say "DoSomething1" and "DoSomething2", so when i call it like :
[self doStuff:#"DoSomething1"];
it will run but if I call it like :
[self doStuff:#"HelloWorld"];
it will give a warning or something?

Answer 1

You should use an enum, like:
typedef enum {
MyStuffOne,
MyStuffTwo,
MyStuffThree
} MyStuff;
- (void)doStuff:(MyStuff)stuff;
thus you will be able to pass only "MyStuff" (MyStuffOne, MyStuffTwo, MyStuffThree)... these are integers and if you want to play with strings, in your method you have to do something like:
NSString *string;
switch (stuff)
{
case MyStuffOne:
string = #"StuffOneString";
break;
default:
...
}

Answer 2

If you need to limit amount of possible values, you should use enumeration data type instead of NSString

Answer 3

Why not just add an if statement into the method like this
- (void)doStuff:(NSString *)doStuffWith{
if([doStuffWith isEqualToString:#"DoSomething1"]){
//do whatever you want here
}else{
//add your warning here
}
}
That should work fine

Answer 4

You could create a method that checks if a word is valid and then assert that method returns true. That would then crash the app if a programmer ever called the method with a bad string, but wouldn't really help if users are able to enter strings themselves. Also, if you use the default project settings, assertions only happen when building with the Debug configuration.
For example:
static NSSet* __validStrings = nil;
- (BOOL)checkString:(NSString*)string
{
if( [string length] == 0 ) return NO;
static dispatch_once_t token;
dispatch_once(&token, ^{
// build the list of valid words once, or load from a plist or something
// if they are very large or change often
NSArray* validWords = [NSArray arrayWithObjects:#"valid", #"doSomething", #"etc.", nil];
__validStrings = [[NSSet alloc] initWithArray:validWords];
});
return [__validStrings containsObject:string];
}
// your doStuff implementation
- (void)doStuff:(NSString*)doStuffWith
{
// This will crash the program and give you debugging information if doStuffWith
// is not in your string list
NSAssert1( [self checkString:doStuffWith], #"invalid string: %#", doStuffWith );
// continue on with your method implementation...
}