How should I be sending a message with a field of the same object as its value?

问题

In Objective-C, the compiler is complaining about the following line of code:

if ([self getLength(self.identifier)] < givenWidth * kMarginAllowance)

This is getting the error "Expected ']'", and the caret below the text is on the parenthesis exactly after "getLength".

My suspicion is that my [self getLength(self.identifier)] is wrong in how it combines things.

What I want to say is "Fetch this object's identifier, and call this object's getLength() method."

I've tried a couple of permutations, and I don't think I'm using correct syntax.

What is the correct syntax for this type of thing?

--

My code is:

-(float)getLength:(NSString *)text
{
    UIFont *font = [UIFont fontWithName:@"Scurlock" size:20];
    CGSize size = [text sizeWithAttributes:[NSDictionary dictionaryWithObjectsAndKeys:font, NSFontAttributeName, nil]];
    return size.width;
}

-(void)getFormattedString:(float)givenHeight width:(float)givenWidth
{
    NSMutableArray *workbench = [NSMutableArray array];
    if (getLength(self.identifier) < givenWidth * kMarginAllowance)
    {
        [workbench addObject:self.identifier];
    }
    else
    {
        // [Under development]
    }
}

The included .h file has:

-(float) getLength:(NSString *)text;

There is a yellow warning in Xcode that indicates that the call to getLength() is an invalid implicit declaration. The character it specifically points to is the beginning of the getLength() call. If I try to run it, I get an "Apple Mach-O Linker Error", because _getLength is referenced and presumably doesn't turn anything up.

What is the root problem I'm causing here? Inlining the method might do what I want, but I'd rather fix it, and understand what the correct approach is.

回答1:

Try

[self getLenght:self.identifier]

So it would be like this:

if ([self getLenght:self.identifier] < givenWidth * kMarginAllowance)

getLenght: is an Objective-C method but you're trying to call it as a C function.

Hope this helps!

回答2:

if ( getLength(self.identifier) < (givenWidth * kMarginAllowance))

回答3:

If getLength is an instance method

// calls getLength method on self.identifier
if ([self.identifier getLength] < givenWidth * kMarginAllowance)

if it is a C style function

if (getLength(self.identifier) < givenWidth * kMarginAllowance)

来源：https://stackoverflow.com/questions/18963566/how-should-i-be-sending-a-message-with-a-field-of-the-same-object-as-its-value