iOS自訂NSDictionary的Key的例子

提出問題：

1.為什麼需要自訂NSDictionary的Key？
2.系統對自訂的Key有什麼要求？

答：

1.我遇到的實際問題是一個三級菜單，每一級都需要記錄是否被選中。我選擇用三個小的tableView來實現這個功能，但是我又要去想什麼樣的資料才能適應這個介面，然後我就想到了用個很大的字典來儲存資訊；
2.首先要實現NSCopying協議裡的copyWithZone，然後要重寫NSObject中的isEqual方法。

代碼如下：

//.h
 
#import <Foundation/Foundation.h>
 
//需要在.h檔案裡就遵守協議，不然會檢測不到是否遵守NSCopying
@interface AreaModel : NSObject<NSCopying>
 
//一些用於記錄資訊的字串屬性
@property (nonatomic,copy) NSString *areaString;
@property (nonatomic,copy) NSString *areaIDString;
//記錄是否選中的屬性
@property (nonatomic,assign) BOOL isSelected;
 
@end
 
//.m
 
#import "AreaModel.h"
 
@interface AreaModel()
//用於判斷兩個對象是否是同一對象的屬性
@property (nonatomic,assign) NSUInteger myHash;
@end
 
@implementation AreaModel
 
#pragma mark -- <NSCopying>
- (id)copyWithZone:(nullable NSZone *)zone
{
    AreaModel *areaModel = [[[self class] allocWithZone:zone] init];
    
    //對象使用copyWithZone
    areaModel.areaString = [self.areaString copyWithZone:zone];
    areaModel.areaIDString = [self.areaIDString copyWithZone:zone];
    //基礎資料類型則簡單賦值
    areaModel.isSelected = self.isSelected;
    areaModel.myHash = self.myHash;
    
    return areaModel;
}
 
- (id)init
{
    self = [super init];
    if (self) {
    //初始化的時候給myHash賦值，值為根據記憶體位址轉為的無符號長整型
        _myHash = (NSUInteger)self;
    }
    return self;
}
 
//有可能非必要重寫get方法
- (NSUInteger)hash
{
    return _myHash;
}
 
//重寫isEqual
- (BOOL)isEqual:(id)object
{
    return self.myHash == ((AreaModel *)object).myHash;
}
 
//為了便於閱讀，所以
#pragma mark -- 重寫description方法
- (NSString *)description
{
    return [NSString stringWithFormat:@"<%@: %p; area = %@; areaID = %@; isSelected = %@>",self.class,self,self.areaString,self.areaIDString,self.isSelected?@"YES":@"NO"];
}
 
@end

最終用到的資料:

AreaModel *pModel1 = [AreaModel new];
pModel1.areaString = @"安徽省";
pModel1.areaIDString = @"01";
 
AreaModel *pModel2 = [AreaModel new];
pModel2.areaString = @"海南省";
pModel2.areaIDString = @"02";
 
AreaModel *cModel1 = [AreaModel new];
cModel1.areaString = @"合肥市";
cModel1.areaIDString = @"0101";
 
AreaModel *cModel2 = [AreaModel new];
cModel2.areaString = @"蕪湖市";
cModel2.areaIDString = @"0102";
 
AreaModel *aModel1 = [AreaModel new];
aModel1.areaString = @"弋江區";
aModel1.areaIDString = @"010201";
aModel1.isSelected = YES;
NSDictionary *dictionary = @{
                             pModel1 : @{
                                     cModel1 : @[],
                                     cModel2 : @[aModel1]
                                     },
                             pModel2 : @{}
                             };