面试题：Objective-C中字典的常见初始化方式有哪些

Question

请列举出Objective-C中字典（NSDictionary和NSMutableDictionary）至少三种常见的初始化方式，并给出相应的代码示例。

Answer 1

1. 使用dictionaryWithObjectsAndKeys:方法初始化NSDictionary

   NSArray *keys = @[@"name", @"age"];
   NSArray *objects = @[@"John", @25];
   NSDictionary *dictionary = [NSDictionary dictionaryWithObjects:objects forKeys:keys];
   

2. 使用initWithDictionary:方法从已有字典初始化NSDictionary

   NSDictionary *originalDict = @{@"name": @"Jane", @"city": @"New York"};
   NSDictionary *newDict = [[NSDictionary alloc] initWithDictionary:originalDict];
   

3. 使用字面量初始化NSDictionary

   NSDictionary *dict = @{@"key1": @"value1", @"key2": @"value2"};
   

4. 使用init方法创建空的NSMutableDictionary，然后使用setObject:forKey:方法添加元素

   NSMutableDictionary *mutableDict = [[NSMutableDictionary alloc] init];
   [mutableDict setObject:@"value3" forKey:@"key3"];
   

5. 使用dictionaryWithCapacity:方法初始化NSMutableDictionary

   NSMutableDictionary *mutableDict2 = [[NSMutableDictionary alloc] initWithCapacity:5];
   [mutableDict2 setObject:@"value4" forKey:@"key4"];
   

6. 使用字面量初始化NSMutableDictionary（iOS 11.0+）

   NSMutableDictionary *mutableDict3 = [@{@"key5": @"value5"} mutableCopy];