NSDictionary及NSMutableDictionary

NSDictionary

1:什么是字典?

OC中的NSDictionary：根据key找到value,字典中存储的东西都是键值对

2:如何创建字典?

方法一:

NSDictionary *dict = [NSDictionary dictionaryWithObject:@"lnj" forKey:@"name"];
//根据key获取value
NSString *name = [dict objectForKey:@"name"];
NSLog(@"name = %@", name);

方法二:

/

/ 注意: key和value 是一一对应
NSDictionary *dict = [NSDictionary dictionaryWithObjects:@[@"lnj", @"30", @"1.75"] forKeys:@[@"name", @"age", @"height"]];
NSLog(@"%@ %@ %@", [dict objectForKey:@"name"], [dict objectForKey:@"age"], [dict objectForKey:@"height"]);

方法三:"简写:

NSDictionary *dict = @{key:value};
NSDictionary *dict = @{@"name": @"lnj"};
NSLog(@"%@", dict[@"name"]);

NSDictionary *dict = @{@"name":@"lnj", @"age":@"30", @"height":@"1.75"};
NSLog(@"%@ %@ %@", dict[@"name"], dict[@"age"], dict[@"height"]);

3:如何对字典进行遍历?

NSDictionary *dict = @{@"name":@"lnj", @"age":@"30", @"height":@"1.75"};

//获取字典中key和value的个数, 在字典中key称之为键, value称之为值
NSLog(@"count = %lu", [dict count]);

方法一:老式for循环写法

for (int i = 0; i < dict.count; ++i) {
    // 获取字典中所有的key
    NSArray *keys = [dict allKeys];
    // 取出当前位置对应的key
    //        NSLog(@"%@", keys[i]);
    NSString *key = keys[i];
    NSString *value = dict[key];
    NSLog(@"key = %@, value = %@", key, value);
}

方法二:增强for循环写法

// 如何通过forin遍历字典, 会将所有的key赋值给前面的obj
for (NSString *key in dict) {
    //        NSLog(@"%@", key);
    NSString *value = dict[key];
    NSLog(@"key = %@, value = %@", key, value);

}

方法三:OC字典的迭代器来遍历

[dict enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
    NSLog(@"key = %@, value = %@", key, obj);
}];

4:如何对字典文件进行读写?

1.将字典数据写入文件中

NSDictionary *dict = @{@"name":@"lnj", @"age":@"30", @"height":@"1.75"};

[dict writeToFile:@"/Users/xiaomage/Desktop/info.plist" atomically:YES];

2.从文件中读取字典数据

• 注意: 字典和数组不同, 字典中保存的数据是无序的

NSDictionary *newDict = [NSDictionary dictionaryWithContentsOfFile:@"/Users/xiaomage/Desktop/info.plist"];
NSLog(@"%@", newDict);

NSArray *arr = @[@10, @20, @30, @5];
[arr writeToFile:@"/Users/xiaomage/Desktop/abc.plist" atomically:YES];

9.NSMutableDictionary

如何对可变字典进行增删改查

1:如何创建一个空的可变字典?

NSMutableDictionary *dictM = [NSMutableDictionary dictionary];

2:如何给可变字典添加键值对?

[dictM setObject:@"lnj" forKey:@"name"];

//简写:
dictM[@"name"] = @"lnj";

// 会将传入字典中所有的键值对取出来添加到dictM中
[dictM setValuesForKeysWithDictionary:@{@"age":@"30", @"height":@"1.75"}];

3:如何根据键,获取可变字典的值?

NSLog(@"name = %@", dictM[@"name"]);

4:如何删除可变字典键值对?

[dictM removeObjectForKey:@"name"];
[dictM removeObjectsForKeys:@[@"age", @"height"]];

5:如何修改可变字典中的键值对?

• 利用setObject方法给同名的key赋值,
  那么新值会覆盖旧值

[dictM setObject:@"88" forKey:@"age"];
//简写:
dictM[@"age"] = @"88";

6:使用可变字典有什么注意事项?

1.不能使用@{}来创建一个可变的字典

    NSMutableDictionary *dictM = @{@"name":@"lnj"};//编译就会报错
    [dictM setObject:@"30" forKey:@"age"];

2.

• 如果是不可变字典, 那么key不能相同
• 如果是不可变字典出现了同名的key,
  那么后面的key对应的值不会被保存
• 如果是在可变数组中, 后面的会覆盖前面的

NSDictionary *dict = @{@"name":@"lmj", @"name":@"lnj"};
NSLog(@"dict = %@", dict);

NSMutableDictionary *dictM = [NSMutableDictionary dictionaryWithObjects:@[@"lmj", @"lnj"] forKeys:@[@"name", @"name"]];
NSLog(@"dict = %@", dictM);