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最新推荐文章于 2020-12-01 15:10:39 发布

zheng3stone

最新推荐文章于 2020-12-01 15:10:39 发布

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本文介绍了Objective-C中可变数组NSMutableArray的使用方法，包括如何添加、移除和替换元素，以及如何对数组进行就地排序。通过示例代码展示了NSMutableArray与NSArray的主要区别。

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今天讲Objective-C的可变数组，之前讲的NSArray是不可变的，immutable，今天讲NSMutableArray，它是可变的。

Mutability

Although the NSArray class itself is immutable, this has no bearing on any collected objects. If you add a mutable string to an immutable array, for example, like this:

NSMutableString *mutableString = [NSMutableString stringWithString:@"Hello"];
NSArray *immutableArray = @[mutableString];

there’s nothing to stop you from mutating the string:

if ([immutableArray count] > 0) {
	id string = immutableArray[0];
	if ([string isKindOfClass:[NSMutableString class]]) {
		[string appendString:@" World!"];
	}
}

If you need to be able to add or remove objects from an array after initial creation, you’ll need to use NSMutableArray, which adds a variety of methods to add , remove or replace one or more objects:

NSMutableArray *mutableArray = [NSMutableArray array];
[mutableArray addObject:@"gamma"];
[mutableArray addObject:@"alpha"];
[mutableArray addObject:@"beta"];

[mutableArray replaceObjectAtIndex:0 withObject:@"epsilon"];

This example creates an array that ends up with the objects @"epsilon", @"alpha", @"beta".

It’s also possible to sort a mutable array in place, without creating a secondary array:

[mutableArray sortUsingSelector:@selector(caseInsensitiveCompare:)];

In this case the contained items will be sorted into the ascending, case insensitive order of @"alpha", @"beta", @"epsilon".