Objective-C：Foundation框架-常用类-NSMutableArray

　　NSMutableArray是NSArray对的子类，它是可变的，可以随意添加或者删除元素。与Array，也有静态和动态两种创建方法。也可已使用NSArray的方法来创建NSMutableArray。当一个元素被加到NSMutableArray中时，会执行一次retain操作；当一个元素从 NSMutableArray中删除时，会执行release操作；当集合被销毁时（调用了dealloc）， NSMutableArray里的所有元素都会执行一次release操作（这个原则也适用于其他集合类型：NSDictionary\NSSet等）。

#import <Foundation/Foundation.h>

@interface Student : NSObject
@property (nonatomic, assign) int age;

+ (id)studentWithAge:(int)age;
@end

#import "Student.h"

@implementation Student

+ (id)studentWithAge:(int)age {
    Student *stu = [[[Student alloc] init] autorelease];
    stu.age = age;
    return stu;
}

- (void)dealloc {
    NSLog(@"[age=%i]被销毁了", _age);
    [super dealloc];
}
@end

#import <Foundation/Foundation.h>
#import "Student.h"

void arrayCreate() {
    NSMutableArray *array = [NSMutableArray arrayWithObject:@""];
    // 添加元素
    [array addObject:@""];
    [array addObject:@""];

    // [array removeObject:@"2"];
    // [array removeLastObject];
    [array removeAllObjects];

    NSLog(@"%@", array);
}

void arrayMemory() {
    NSMutableArray *array = [[NSMutableArray alloc] init];
    // stu1:1
    Student *stu1 = [[Student alloc] init];
    stu1.age = ;
    // stu2:1
    Student *stu2 = [[Student alloc] init];
    stu2.age = ;

    // 对被添加的元素做一次retain操作，计数器+1
    [array addObject:stu1]; // stu1:2
    [array addObject:stu2]; // stu2:2

    NSLog(@"add->stu1:%zi", [stu1 retainCount]);

    // 对被删除的元素做一次release操作，计数器-1
    [array removeObject:stu1]; // stu1:1

    NSLog(@"remove->stu1:%zi", [stu1 retainCount]);

    // 释放学生
    [stu1 release]; // stu1:0
    [stu2 release]; // stu2:1

    // 当数组被释放的时候，会对所有的元素都做一次release操作
    [array release]; // stu2:0
}

void arrayReplace() {
    NSMutableArray *array = [NSMutableArray arrayWithObjects:@"", @"", @"", nil];

    [array replaceObjectAtIndex: withObject:@""];

    NSLog(@"%@", array);
}

void arraySort() {
    NSMutableArray *array = [NSMutableArray arrayWithObjects:@"", @"", @"", nil];

    [array sortUsingSelector:@selector(compare:)];

    NSLog(@"%@", array);
}