本文对Foundation框架中的字典类（NSDictionary和NSMutableDictionary）的使用做一个详细的总结。
1. NSDictionary
1.NSDictionar 介绍
- Dictionary翻译过来叫做"字典"
- 日常生活中，“字典”的作用：通过一个拼音或者汉字，就能找到对应的详细解释
- NSDictionary的作用类似：通过一个键（key），就能找到对应的值（value）
- NSDictionary中的键（key）是单值，通常是字符串，也可以是其他对象类型
- NSDictionary中和键（key）关联的值（value）可以是任何对象类型，但不能是nil
- NSDictionary是不可变的，一旦初始化完毕，里面的内容就无法修改
2.NSDictionary 的创建
+ (instancetype)dictionary;
+ (instancetype)dictionaryWithObject:(id)object forKey:(id <NSCopying>)key;
+ (instancetype)dictionaryWithObjectsAndKeys:(id)firstObject, ...;
+ (id)dictionaryWithContentsOfFile:(NSString *)path;
+ (id)dictionaryWithContentsOfURL:(NSURL *)url;
3. NSDictionary 创建和获取简写
- 以前 NSDictionary 创建方式
NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:@"Walkers", @"name", @"12345678", @"phone", @"ZhongGuo", @"address", nil];
NSDictionary *dict = [NSDictionary dictionaryWithObjects:@[@"Walkers",@"30",@"1.75"] forKeys:@[@"name",@"age",@"height"]];
- 现在 NSDictionary 创建简写方式
NSDictionary *dict = @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"};
- 以前NSDictionary获取元素方式
[dict objectForKey:@"name”];
- 现在NSDictionary获取元素简写方式
dict[@"name”];
4. 键值对集合的特点
- 字典存储的时候，必须是"键值对"的方式来存储(同时键不要重复)
- 键值对中存储的数据是"无序的"
- 键值对集合可以根据键，快速获取数据
5. NSDictionary的遍历
- 返回字典的键值对数目
- (NSUInteger)count;
NSDictionary *dict = @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"};
NSLog(@"count = %lu",[dict count]);
输出结果：count = 3
- 根据key取出value
- (id)objectForKey:(id)aKey;
NSDictionary *dict = @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"};
NSLog(@"%@",[dict objectForKey:@"name"]);
输出结果：Walkers
- 快速遍历
NSDictionary *dict = @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"};
for (NSString *key in dict) {
NSLog(@"key = %@, value = %@", key, dict[key]);
}
输出结果：
key = name, value = Walkers
key = phone, value = 12345678
key = address, value = ZhongGuo
- Block遍历
[dict enumerateKeysAndObjectsUsingBlock:^(NSString *key, NSString *obj, BOOL *stop) {
NSLog(@"key = %@, value = %@", key, obj);
}];
6. NSDictionary文件操作
- 将字典写入文件中
- (BOOL)writeToFile:(NSString *)path atomically:(BOOL)useAuxiliaryFile;- (BOOL)writeToURL:(NSURL *)url atomically:(BOOL)atomically;- 存储结果是xml文件格式，但苹果官方推荐为plist后缀
- 示例
NSDictionary *dict = @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"};
BOOL flag = [dict writeToFile:@"/Users/Walkers/Desktop/dict.plist" atomically:YES];
NSLog(@"flag = %i", flag);
输出结果：flag = 1
文件里的内容显示结果如下图
1.png
- 从文件中读取字典
NSDictionary *newDict = [NSDictionary dictionaryWithContentsOfFile:@"/Users/Walkers/Desktop/dict.plist"];
NSLog(@"newDict = %@", newDict);
7. NSDictionary和NSArray对比
1. NSDictionary和NSArray的区别
- NSArray是有序的，NSDictionary是无序的
- NSArray是通过下标访问元素，NSDictionary是通过key访问元素
2. NSDictionary和NSArray的用法
- 创建
// 数组
@[@"Walkers", @"Rose"] (返回是不可变数组)
// 字典
@{ @"name" : @"Walkers", @"phone" : @"12345678" } (返回是不可变字典)
- 访问
// 数组
id d = array[1];
// 字典
id d = dict[@"name"];
- 赋值
// 数组
array[1] = @"Walkers";
// 字典
dict[@"name"] = @"Walkers";
2. NSMutableDictionary
1. NSMutableDictionary 介绍
- NSMutableDictionary 是 NSDictionary 的子类
- NSDictionary 是不可变的，一旦初始化完毕后，它里面的内容就永远是固定的，不能删除里面的元素，也不能再往里面添加元素
- NSMutableDictionary 是可变的，随时可以往里面添加\更改\删除元素
2. NSMutableDictionary 的常见操作
- 添加/修改一个键值对(如果 aKey 之前有值，则会把 aKey 之前对应的值给替换掉)
- (void)setObject:(id)anObject forKey:(id <NSCopying>)aKey;
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
[dict setObject:@"Walkers" forKey:@"name"];
NSLog(@"%@", dict);
输出结果：
{
name = Walkers;
}
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
[dict setObject:@"Walkers" forKey:@"name"];
NSLog(@"%@", dict);
[dict setObject:@"abc" forKey:@"name"];
NSLog(@"%@", dict);
输出结果：
{
name = Walkers;
}
{
name = abc;
}
- 通过aKey删除对应的value
- (void)removeObjectForKey:(id)aKey;
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
[dict setValuesForKeysWithDictionary: @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"}];
[dict removeObjectForKey:@"name"];
NSLog(@"%@",dict);
输出结果：
{
address = ZhongGuo;
phone = 12345678;
}
- 删除所有的键值对
- (void)removeAllObjects;
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
[dict setValuesForKeysWithDictionary: @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"}];
[dict removeAllObjects];
NSLog(@"%@",dict);
输出结果：
{
}
3. NSMutableDictionary 的简写
- 以前设置键值对方式
[dict setObject:@"Jack" forKey:@"name”];
- 现在设置键值对方式
dict[@"name"] = @"Jack";
