加了$能直接取{}里面的值,如果没有加,则会显示{this.mainReceiver}这类值。例子:不加$:要显示m_a,m_bConsole.WriteLine("this is a:{0},this is b:{1}",m_a,m_b));加$:可将值直接放{}里:Console.WriteLine($"this is a:{m_a} ,this is b:{m_b}");