protected Command(Receiver receiver)
{
this.receiver = receiver;
}
public CommandPattern()
{
Receiver receiver = new Receiver();
Command command = new ConcreteCommand(receiver);
Invoker invoker = new Invoker();
invoker.SetCommand(command);
invoker.ExecuteCommand();
command = null;
invoker.ExecuteCommand();
//把command赋值为空，但请求者实体里面的command没变，所以还是会执行
}
public ConcreteCommand(Receiver receiver)
: base(receiver)
{
}