37-oc NSDictionary

Posted 2020-06-18 wc&Home

NSDictionary

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

 

如何创建字典

方法一:

NSDictionary *dict = [NSDictionary dictionaryWithObject:@"lj" 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:@[@"lj", @"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": @"lj"};

NSLog(@"%@", dict[@"name"]);

 

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

NSLog(@"%@ %@ %@", dict[@"name"], dict[@"age"], dict[@"height"]);

 

---

 

如何对字典进行遍历

NSDictionary *dict = @{@"name":@"lj", @"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);

}];

 

---

 

 字典文件进行读写

将字典数据写入文件中

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

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

 

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];

 

---

 

 NSMutableDictionary

如何对可变字典进行增删改查

如何创建一个空的可变字典

NSMutableDictionary *dictM = [NSMutableDictionary dictionary];

 

如何给可变字典添加键值对

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

//简写:

dictM[@"name"] = @"lj";

// 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"}];

 

如何根据键,获取可变字典的值

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

 

如何删除可变字典键值对 

[dictM removeObjectForKey:@"name"];

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

 

 

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";

 

---

 

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":@"lj"};//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":@"lm", @"name":@"lj"};

NSLog(@"dict = %@", dict);

 

NSMutableDictionary *dictM = [NSMutableDictionary dictionaryWithObjects:@[@"lmj", @"lj"] forKeys:@[@"name", @"name"]];

NSLog(@"dict = %@", dictM);

 

NSArray和NSDictionary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