What is NSAssert1?

问题:

I am developing an application on iOS. I see there is a macro called NSAssert1. What is it for? What are the differences in usage between NSLog and NSAssert1?

Please guide me or suggest a tutorial where I can read about it.

回答1:

NSAssert variants take a condition and a message. If the condition isn't met/true, then the assertion fails and NSAssert raises an exception with the message provided. For example, NSAssert((a == b), @"Error message"); will raise an exception when a is not equal to b. NSAssert1 is a variant that takes an additional argument and inserts it into the format string provided, like so: NSAssert1((a == b), @"Error message: %@", someErrorString);

NSLog will just write something to the console.

Documentation for all of those macros is on Apple's developer site.

回答2:

NSAssert, NSParameterAssert, NSAssert1, and friends are assertion macros. Assertions are condition checks that scream when something is not right:

- (void) doSomethingWithPointer: (Foo*) foo
{
    NSAssert(foo != NULL, @"The Foo pointer must not be NULL!");
    foo->something;
}

See questions tagged “assertions” here on Stack Overflow for more information.