Effective Objective-C 2.0 Reading Notes

最新推荐文章于 2025-08-16 22:13:48 发布

转载最新推荐文章于 2025-08-16 22:13:48 发布 · 213 阅读

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原文链接：http://www.cnblogs.com/davidgu/p/3731526.html

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#移动开发

本文深入探讨了Objective-C中的字面量语法，包括字符串、数字、数组和字典的字面量创建方式，以及使用字面量时需要注意的特殊情况，如处理nil值时的异常处理。

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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