swift方便初始化程序调用其他便利初始化程序从超类继承

Question

class AreaSectorLineOverlay: MKPolyline {
var id: String!
var nickName: String!
var locationName: String!

convenience init(coordinates coords: UnsafePointer<CLLocationCoordinate2D>, count: Int, id: String, nickName: String, locationName: String) {
    self.init(coordinates: coords, count: count)
    self.id = id
    self.nickName = nickName
    self.locationName = locationName
}

}

为什么代码错了？错误是（＆＃39; self＆＃39;在self.init调用之前使用）和最后一个函数＆＃init;（坐标coords：UnsafePointer，count：Int，id：String，nickName：String，locationName：String ）＆＃39;错误是（在从初始化程序返回之前，所有路径都没有调用Self.init）

class A {
    var a1: String!

    init() {
    }

    convenience init(a1: String) {
        self.init()
        self.a1 = a1
    }
 }

 class B: A {
     var b1: String!

     convenience init(a1: String, b1: String) {
         self.init(a1: a1)
         self.b1 = b1
     }
 }

 let b = B(a1: "a1Test", b1: "b1Test")
 print(b.a1, b.b1)

没有这样的错误，打印结果是（a1Test b1Test）