OC 知识:Foundation 框架详尽总结之『字典类』

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

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+ (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
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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
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NSDictionary *dict = @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"};
  • 以前NSDictionary获取元素方式
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[dict objectForKey:@"name”];
  • 现在NSDictionary获取元素简写方式
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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;
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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;
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NSDictionary *dict = @{@"name":@"Walkers", @"phone":@"12345678", @"address":@"ZhongGuo"};
NSLog(@"%@",[dict objectForKey:@"name"]);

输出结果:Walkers
  • 快速遍历
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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
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[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
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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
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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
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// 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
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// 数组
id d = array[1];
// 字典
id d = dict[@"name"];
  • 赋值
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// 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;
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NSMutableDictionary *dict = [NSMutableDictionary dictionary];

[dict setObject:@"Walkers" forKey:@"name"];
NSLog(@"%@", dict);

输出结果:
{
name = Walkers;
}
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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;
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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;
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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
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[dict setObject:@"Jack" forKey:@"name”];
  • 现在设置键值对方式
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dict[@"name"] = @"Jack";
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