iOS Fundation-NSDictionary & NSMutableDictionary 使用详解

目前我们经常使用的 NSString、NSArray和NSMutableArray，下面小编将向大家展示 NSDictionary 和 NSMutableDictionary 相关 API 和一些使用方法。

翻看开发文档可以看到下面这段话：

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Neither a key nor a value can be nil; if you need to represent a null value in a dictionary, you should use NSNull.
//在 NSDictionary 不可以使用 nil 值，如果要使用可以使用 NSNull 来进行设置值

NSDictionary

NSDictionary 是使用 Key-Value 的形式来进行对值查找和管理，继承自 NSObject：

NSDictionary 的继承代码如下：

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@interface NSDictionary<__covariant KeyType, __covariant ObjectType> : NSObject
  • NSDictionary初始化

NSDictionary初始化的 API：

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//使用类方法 来进行实例化 dictionary 
+ (instancetype)dictionary;
+ (instancetype)dictionaryWithObject:(ObjectType)object forKey:(KeyType <NSCopying>)key;
#if TARGET_OS_WIN32
+ (instancetype)dictionaryWithObjects:(const ObjectType _Nonnull [_Nullable])objects forKeys:(const KeyType _Nonnull [_Nullable])keys count:(NSUInteger)cnt;
#else
+ (instancetype)dictionaryWithObjects:(const ObjectType _Nonnull [_Nullable])objects forKeys:(const KeyType <NSCopying> _Nonnull [_Nullable])keys count:(NSUInteger)cnt;
#endif

+ (instancetype)dictionaryWithObjectsAndKeys:(id)firstObject, ... NS_REQUIRES_NIL_TERMINATION NS_SWIFT_UNAVAILABLE("Use dictionary literals instead");

+ (instancetype)dictionaryWithDictionary:(NSDictionary<KeyType, ObjectType> *)dict;
+ (instancetype)dictionaryWithObjects:(NSArray<ObjectType> *)objects forKeys:(NSArray<KeyType <NSCopying>> *)keys;

//使用实例方法 来进行实例化 dictionary
- (instancetype)initWithObjectsAndKeys:(id)firstObject, ... NS_REQUIRES_NIL_TERMINATION;
- (instancetype)initWithDictionary:(NSDictionary<KeyType, ObjectType> *)otherDictionary;
- (instancetype)initWithDictionary:(NSDictionary<KeyType, ObjectType> *)otherDictionary copyItems:(BOOL)flag;
- (instancetype)initWithObjects:(NSArray<ObjectType> *)objects forKeys:(NSArray<KeyType <NSCopying>> *)keys;

//从 URL 来获取 dictionary 
/* Reads dictionary stored in NSPropertyList format from the specified url. */
- (nullable NSDictionary<NSString *, ObjectType> *)initWithContentsOfURL:(NSURL *)url error:(NSError **)error API_AVAILABLE(macos(10.13), ios(11.0), watchos(4.0), tvos(11.0));

/* Reads dictionary stored in NSPropertyList format from the specified url. */

//使用 URL 和 Path 路径来初始化 dictionary
+ (nullable NSDictionary<KeyType, ObjectType> *)dictionaryWithContentsOfFile:(NSString *)path;
+ (nullable NSDictionary<KeyType, ObjectType> *)dictionaryWithContentsOfURL:(NSURL *)url;
- (nullable NSDictionary<KeyType, ObjectType> *)initWithContentsOfFile:(NSString *)path;
- (nullable NSDictionary<KeyType, ObjectType> *)initWithContentsOfURL:(NSURL *)url;

NSDictionary初始化实例：

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//NSDictionary 使用字面量来进行初始化
NSDictionary *dictionary = @{
                                 @"helloString" : @"Hello, World!",
                                 @"magicNumber" : @42,
                                 };
    
//使用提供的接口来进行初始化   
id objects[] = {@"Hello, World!", @42};
id keys[] = {@"helloString", @"magicNumber"};
NSUInteger count = sizeof(objects) / sizeof(id);
NSDictionary *dictionary1 = [NSDictionary dictionaryWithObjects:objects
                                                           forKeys:keys
                                                             count:count];
  • NSDictionary常用方法
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//获取相关的属性
@property (readonly, copy) NSArray<KeyType> *allKeys;//获取所有的Key
- (NSArray<KeyType> *)allKeysForObject:(ObjectType)anObject;//获取 Object 对应的 keys
@property (readonly, copy) NSArray<ObjectType> *allValues;//获取所有的 Values 值
@property (readonly, copy) NSString *description;//dictiosnary 的描述
@property (readonly, copy) NSString *descriptionInStringsFileFormat;//

//常用的 API 接口的使用 
- (NSString *)descriptionWithLocale:(nullable id)locale;
- (NSString *)descriptionWithLocale:(nullable id)locale indent:(NSUInteger)level;
- (BOOL)isEqualToDictionary:(NSDictionary<KeyType, ObjectType> *)otherDictionary;//判断两个 dictionary 是否相同
- (NSEnumerator<ObjectType> *)objectEnumerator;//使用枚举
- (NSArray<ObjectType> *)objectsForKeys:(NSArray<KeyType> *)keys notFoundMarker:(ObjectType)marker;//根据相关的 key 来上进行获取 Object
- (BOOL)writeToURL:(NSURL *)url error:(NSError **)error API_AVAILABLE(macos(10.13), ios(11.0), watchos(4.0), tvos(11.0));//把 dictionary 写入到给定的 URL 路径
- (NSArray<KeyType> *)keysSortedByValueUsingSelector:(SEL)comparator;
- (void)getObjects:(ObjectType _Nonnull __unsafe_unretained [_Nullable])objects andKeys:(KeyType _Nonnull __unsafe_unretained [_Nullable])keys count:(NSUInteger)count API_AVAILABLE(macos(10.7), ios(5.0), watchos(2.0), tvos(9.0)) NS_SWIFT_UNAVAILABLE("Use 'allKeys' and/or 'allValues' instead");

- (nullable ObjectType)objectForKeyedSubscript:(KeyType)key API_AVAILABLE(macos(10.8), ios(6.0), watchos(2.0), tvos(9.0));

//使用枚举实现遍历 dictionary 中的 values
- (void)enumerateKeysAndObjectsUsingBlock:(void (NS_NOESCAPE ^)(KeyType key, ObjectType obj, BOOL *stop))block API_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));
- (void)enumerateKeysAndObjectsWithOptions:(NSEnumerationOptions)opts usingBlock:(void (NS_NOESCAPE ^)(KeyType key, ObjectType obj, BOOL *stop))block API_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));

- (NSArray<KeyType> *)keysSortedByValueUsingComparator:(NSComparator NS_NOESCAPE)cmptr API_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));
- (NSArray<KeyType> *)keysSortedByValueWithOptions:(NSSortOptions)opts usingComparator:(NSComparator NS_NOESCAPE)cmptr API_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));

- (NSSet<KeyType> *)keysOfEntriesPassingTest:(BOOL (NS_NOESCAPE ^)(KeyType key, ObjectType obj, BOOL *stop))predicate API_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));
- (NSSet<KeyType> *)keysOfEntriesWithOptions:(NSEnumerationOptions)opts passingTest:(BOOL (NS_NOESCAPE ^)(KeyType key, ObjectType obj, BOOL *stop))predicate API_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));

//把数据写入本地的 file 或者 URL  文件
- (BOOL)writeToFile:(NSString *)path atomically:(BOOL)useAuxiliaryFile;
- (BOOL)writeToURL:(NSURL *)url atomically:(BOOL)atomically;
  • NSDictionary 遍历

NSDictionary实现遍历代码：

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NSDictionary *dictionary = @{
                                 @"helloString" : @"Hello, World!",
                                 @"magicNumber" : @42,
                                 @"name" : @"liang",
                                 @"name" : @"Jin",
                                 @"first name" : @"bai",
                                 @"home" : @"guangdong"
                                 };
 __block int count = 0;
[dictionary enumerateKeysAndObjectsUsingBlock:^(id  _Nonnull key, id  _Nonnull obj, BOOL * _Nonnull stop) {
      NSLog(@"the index %d content : %@", count, obj);
      count ++;
}];

//    [dictionary enumerateKeysAndObjectsWithOptions:nil usingBlock:^(id  _Nonnull key, id  _Nonnull obj, BOOL * _Nonnull stop) {
//        NSLog(@"the index %d content : %@", count, obj);
//        count ++;
//    }];
//这里可以设置 NSEnumerationOptions 来设置遍历过程

//打印结果：
//Fundation-Demo[55047:16781022] the index 0 content : bai
//Fundation-Demo[55047:16781022] the index 1 content : guangdong
//Fundation-Demo[55047:16781022] the index 2 content : Hello, World!
//Fundation-Demo[55047:16781022] the index 3 content : 42
//Fundation-Demo[55047:16781022] the index 4 content : liang
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//下面是使用断点，来查看 dictionary 在内存上地址和依次保存的位置
Printing description of dictionary:
{
    "first name" = bai;
    helloString = "Hello, World!";
    home = guangdong;
    magicNumber = 42;
    name = liang;
}
(__lldb_autogen_nspair) [0] = {
  key = 0x000000010a3ec210
  value = 0x000000010a3ec230
}
(__lldb_autogen_nspair) [1] = {
  key = 0x000000010a3ec250
  value = 0x000000010a3ec270
}
(__lldb_autogen_nspair) [2] = {
  key = 0x000000010a3ec150
  value = 0x000000010a3ec170
}
(__lldb_autogen_nspair) [3] = {
  key = 0x000000010a3ec190
  value = 0xb0000000000002a2
}
(__lldb_autogen_nspair) [4] = {
  key = 0x000000010a3ec1b0
  value = 0x000000010a3ec1d0
}

可以看出在使用 enumerateKeysAndObjectsUsingBlock: 遍历过程是得到无序的结果，而且在保存过程中 NSDictioary 是按照字幕的顺序表进行保存。

NSMutableDictionary

  • NSMutableDictionary 继承关系
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@interface NSMutableDictionary<KeyType, ObjectType> : NSDictionary<KeyType, ObjectType>
``` 

* `NSMutableDictionary` 初始化

```objc
+ (instancetype)dictionaryWithCapacity:(NSUInteger)numItems;

//通过 File 和 path 来获取 `NSMutableDictionary` 实例
+ (nullable NSMutableDictionary<KeyType, ObjectType> *)dictionaryWithContentsOfFile:(NSString *)path;
+ (nullable NSMutableDictionary<KeyType, ObjectType> *)dictionaryWithContentsOfURL:(NSURL *)url;
- (nullable NSMutableDictionary<KeyType, ObjectType> *)initWithContentsOfFile:(NSString *)path;
- (nullable NSMutableDictionary<KeyType, ObjectType> *)initWithContentsOfURL:(NSURL *)url;
  • NSMutableDictionary 常用 API 接口
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//修改参数 & 初始化
- (void)removeObjectForKey:(KeyType)aKey;
- (void)setObject:(ObjectType)anObject forKey:(KeyType <NSCopying>)aKey;
- (instancetype)init NS_DESIGNATED_INITIALIZER;
- (instancetype)initWithCapacity:(NSUInteger)numItems NS_DESIGNATED_INITIALIZER;
- (nullable instancetype)initWithCoder:(NSCoder *)aDecoder NS_DESIGNATED_INITIALIZER;

//修改 dictioanry 中的 Object 对象
- (void)addEntriesFromDictionary:(NSDictionary<KeyType, ObjectType> *)otherDictionary;
- (void)removeAllObjects;
- (void)removeObjectsForKeys:(NSArray<KeyType> *)keyArray;
- (void)setDictionary:(NSDictionary<KeyType, ObjectType> *)otherDictionary;
- (void)setObject:(nullable ObjectType)obj forKeyedSubscript:(KeyType <NSCopying>)key API_AVAILABLE(macos(10.8), ios(6.0), watchos(2.0), tvos(9.0));

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