Objective-C如何自己实现一个基于数组下标的属性访问模式

原文地址：http://www.cnblogs.com/zenny-chen/p/3593660.html

在iOS6.0以及OS X10.8之后，Apple引入了一套非正式协议（informal protocol）与Objective-C语法直接绑定。当你实现了这其中的方法之后即可使用数组下标来访问属性元素。

在Foundation库中，NSArray类实现了- (id)objectAtIndexedSubscript:(NSUInteger)idx方法。因此，我们可以这么来访问数组元素：

NSArray *arr = @[@100, @200, @300];NSNumber *num = arr[0];

上述arr[0]就相当于[arr objectAtIndex:0]。

而NSMutableArray在基于NSArray的基础上又实现了- (void)setObject:(id)anObject atIndexedSubscript:(NSUInteger)index方法。这样我们可以通过数组下标来读写相应元素，比如：

NSMutableArray *arr = [NSMutableArray arrayWithArray:@[@100, @200, @300]];arr[2] = arr[0];

而NSDictionary类实现了- (id)objectForKeyedSubscript:(id)key方法。这样我们能以数组下标的形式来访问相应键的值。比如：

NSDictionary *dict = @{@"key" : @"value"};NSString *value = dict[@"key"];

而NSMutableDictionary在NSDictionary类的基础上又实现了- (void)setObject:(id)object forKeyedSubscript:(id < NSCopying >)aKey方法。这样，我们能以数组下标的方式来读写相应键的值。比如：

NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithDictionary:@{@"key":"@Hello"}];dict[dict[@"key"]] = @"world";

下面我们通过实现这四个方法，自己实现一个能同时使用这四种下标方式访问模式的类。

////  main.m//  objCTest////  Created by Zenny Chen on 12-2-7.//  Copyright (c) 2014年 Neon Media Studio. All rights reserved.//#import <Foundation/Foundation.h>@interface MyContainer : NSObject{@private    NSMutableDictionary *mDict;    NSMutableArray *mArray;}- (void)setObject:(id)object forKeyedSubscript:(id < NSCopying >)aKey;- (id)objectForKeyedSubscript:(id)key;- (void)setObject:(id)anObject atIndexedSubscript:(NSUInteger)index;- (id)objectAtIndexedSubscript:(NSUInteger)idx;@end@implementation MyContainer- (instancetype)init{    self = [super init];    mDict = [[NSMutableDictionary alloc] initWithDictionary:@{@"key1":@"value1", @"key2":@"value2"}];    mArray = [[NSMutableArray alloc] initWithArray:@[@100, @200, @300, @400]];    return self;}- (void)dealloc{    if(mDict != nil)    {        [mDict removeAllObjects];        [mDict release];        mDict = nil;    }    if(mArray != nil)    {        [mArray removeAllObjects];        [mArray release];        mArray = nil;    }    [super dealloc];}- (void)setObject:(id)object forKeyedSubscript:(id < NSCopying >)aKey{    [mDict setObject:object forKey:aKey];}- (id)objectForKeyedSubscript:(id)key{    return [mDict objectForKey:key];}- (void)setObject:(id)anObject atIndexedSubscript:(NSUInteger)index{    const NSUInteger length = [mArray count];    if(index > length)        return;    if(index == length)        [mArray addObject:anObject];    else        [mArray replaceObjectAtIndex:index withObject:anObject];}- (id)objectAtIndexedSubscript:(NSUInteger)idx{    if(idx >= [mArray count])        return nil;    return [mArray objectAtIndex:idx];}@endint main (int argc, const char * argv[]){    @autoreleasepool    {        // insert code here...        MyContainer *cont = [[MyContainer alloc] init];        cont[@"mykey"] = @"myvalye";        NSLog(@"key1 is: %@", cont[@"key1"]);        NSLog(@"key2 is: %@", cont[@"key2"]);        NSLog(@"mykey is: %@", cont[@"mykey"]);        cont[4] = @500;        cont[2] = @-300;        NSLog(@"The value[4] = %@", cont[4]);        NSLog(@"The value[3] = %@", cont[3]);        NSLog(@"The value[2] = %@", cont[2]);    }    return 0;}