【OC梳理】NSDirctionary、NSMutableDir

NSDirctionary

NSDirctionary(字典)，以键值对的形式存放数据，常用方法如下：
创建

NSObject *obj1 = [NSObject new];
NSObject *obj2 = [NSObject new];
//对象方法，对应的类方法以dictionaryWith开头
NSDictionary *dict1 = [[NSDictionary alloc] initWithObjectsAndKeys:obj1,@"obj1",obj2,@"obj2", nil];
NSDictionary *dict2 = [[NSDictionary alloc]initWithObjects:@[obj1,obj2] forKeys:@[@"obj1",@"obj2"]];

NSDictionary *dict3 = @{@"obj1":obj1,@"obj2":obj2};

//单个元素的字典
NSDictionary *dict4 = [NSDictionary dictionaryWithObject:obj1 forKey:@"obj1"];

获取所有的key

NSArray *allKeys = [dict allKeys];  

获取所有的value

NSArray *allValues = [dict allValues]; 

通过key获取value

NSObject *value = [dict1 objectForKey:@"obj1"]; 
NSObject *value1 = dict1[@"obj1"];

NSMutableDirctionary

NSMutableDirctionary(可变字典)，继承于NSDictionary，并扩充了增删改功能：
创建

NSObject *obj1 = [NSObject new];
NSObject *obj2 = [NSObject new];
NSMutableDictionary *md1 = [[NSMutableDictionary alloc] initWithCapacity:3];
NSMutableDictionary *md2 = [[NSMutableDictionary alloc]initWithObjects:@[obj1,obj2] forKeys:@[@"obj1",obj2]];
NSMutableDictionary *md3 = [[NSMutableDictionary alloc]initWithObjectsAndKeys:obj1,@"obj1",obj2,@"obj2", nil];
NSMutableDictionary *md4 = [[NSMutableDictionary alloc]initWithDictionary:dic1];