按两个值对数组进行排序Swift 4

Question

目前，我通过执行以下操作

进行排序和排列

self.list = self.list.sorted(by: { $0.priority < $1.priority })

但我也是要通过第二个属性number

对数组进行排序的方法

Class Item {
   var number: Int = 0
   var priority: Int = 0
}

数组应按如下顺序显示，

priority = 1, number = 3
priority = 1, number = 4
priority = 1, number = 5
priority = 1, number = 7
priority = 2, number = 1
priority = 2, number = 5

但是截至目前显示如下

priority = 1, number = 7
priority = 1, number = 5
priority = 1, number = 3
priority = 1, number = 4
priority = 2, number = 5
priority = 2, number = 1

我认为也许这样可以工作，

self.list = self.list.sorted(by: { $0.priority < $1.priority && $0.number < $1.number })

但是它根本不排序。有人知道我如何对数组进行排序吗？