Question

I have an NSString that is stored in Core Data. It is optional, which I believe in the sqlite db means it can be null. I have a convenience method I call ‘isEmptyOrWhitespace’ shown here:

- (BOOL)isEmptyOrWhiteSpace {
    return self == nil ||
    self.length == 0 ||
    [self stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]].length == 0;
}

When my string from Core Data is nil, it doesn’t seem to call this method, that is the breakpoints are never hit. This is particularly annoying because a code chunk like this:

if(![string isEmptyOrWhitespace]) {
    [string doSomething];
}

doSomething is being run if string is nil, obviously not my intent. Is there a way to get around this without checking if my string is nil before calling a method on it? Or is this a “feature” of Objective-C that methods aren’t run on nil objects?

Answer 1

If string is nil, then [string isEmptyOrWhitespace] does nothing, because sending messages to nil is a no-op.

EDIT: As @Jim pointed out, this answer is not correct. [nil isEmptyOrWhitespace] returns 0, and that is the real reason that the if () block is not executed if string = nil.