1. Literal Syntax
NSString *someString = @"Effective Objective-C 2.0";
NSNumber *someNumber = [NSNumber numberWithInt:1];
<=>
NSNumber *someNumber = @1;
// syntax also works for expressions
int x = 5;
float y = 6.32f;
NSNumber *expressionNumber = @(x * y);
NSArray *animals =
[NSArray arrayWithObjects:@"cat", @"dog",
@"mouse", @"badger", nil];
<=>
NSArray *animals = @[@"cat", @"dog", @"mouse", @"badger"];
NSString *dog = [animals objectAtIndex:1];
<=>
NSString *dog = animals[1];
However, you need to be aware of one thing when creating arrays using the literal
syntax. If any of the objects is nil, an exception is thrown
a scenario:
id object1 = /* ... */;
id object2 = /* ... */;
id object3 = /* ... */;
NSArray *arrayA = [NSArray arrayWithObjects:
object1, object2, object3, nil];
NSArray *arrayB = @[object1, object2, object3];
Now consider the scenario in which object1 and object3 point to valid Objective-C
objects, but object2 is nil. The literal array, arrayB, will cause the exception to be thrown.
However, arrayA will still be created but will contain only object1. The reason is that the
arrayWithObjects: method looks through the variadic arguments until it hits nil, which is
sooner than expected.
It’s much better that an exception is thrown, causing a probable application crash, rather than creating an array
having fewer than the expected number of objects in it.
// Literal Dictionaries
NSDictionary *personData =
[NSDictionary dictionaryWithObjectsAndKeys:
@"Matt", @"firstName", @"Galloway", @"lastName",
[NSNumber numberWithInt:28], @"age", nil];
<=>
NSDictionary *personData =
@{@"firstName" : @"Matt",
@"lastName" : @"Galloway",
@"age" : @28};
NSString *lastName = [personData objectForKey:@"lastName"];
<=>
NSString *lastName = personData[@"lastName"];
转载于:https://www.cnblogs.com/davidgu/p/3731526.html