Question

I’m trying to change a variable of NSString type by calling a method. But it doesn’t work. I tried this very same method with othe types and it worked perfectly fine. Can you help me out there?

Interface:

- (void) changeNSString: (NSString *) stringToChange;

Implementation:

- (void) changeNSString: (NSString *) stringToChange{

    stringToChange = @"Test";    
}

- (IBAction)actionBla:(id)sender {

    NSString *myString = [NSString string];
    [self changeNSString:myString];
    NSLog(myString);            //Returns nothing or empty string

}

======================
Edit: thanks to the help of CrimsonDiego, here is a working solution. Though I still have a little understanding issue: why is there no type-error when assigning a NSMutableString to a NSString var?

Interface:

- (void) changeNSMutableString: (NSMutableString *) stringToChange;

Implementation:

- (void) changeNSMutableString: (NSMutableString *) stringToChange{

    [stringToChange setString:@"Test"]    
}

- (IBAction)actionBla:(id)sender {

    NSMutableString *myString = [NSMutableString string];
    [self changeNSMutableString:myString];
    self.myLabel.text = myString;           //Why is there no type error???

}

Answer 1

You are assigning a new variable to a local variable within the function.

The local variable stringToChange references the same variable as myString at first, but when you assign @”Test” to stringToChange, it no longer references the original string.

The solution here would be to use NSMutableString, or have a class variable (or property) and use that instead of passing it to the function.