追加到数组后，我无法修改该项目 [英] I cannot modify the item after appending to array

问题描述

我正在开发Unity Engine的多人api。我有Room和RoomManager结构。当我想创建房间时，我设置了房间名称，id（所有变量），之后我将这个新房间添加到RoomManager结构中的所有房间数组中。之后，当我修改为房间变量时，我无法更改任何变量。我不知道为什么？

以下是我的结构和方法：

RoomManager结构

  type RoomManager struct {
 allRooms [] Room 
 roomCounter int 
} 
  

房间结构

 类型房间结构{
标记字符串
名称字符串
密码字符串
 id int 
 cappacity int 
 maxVariableCount int 
 userList []用户
房间变量[] RoomVariable 
 ExtensionHandlers [] ExtensionRequest 
 InitializeMethod roomInitializeFunc 
} 
  

房间创建方法

  func（roomManager * RoomManager）CreateRoom（设置RoomSettings，arwServer * ARWServer）* Room {
 
 var newRoom Room 
 newRoom.InitializeMethod = settings.InitializeMethod 
 
 newRoom.name = settings.name 
 newRoom.password = settings.p密码
 newRoom.tag = settings.tag 
 newRoom.cappacity = settings.cappacity 
 newRoom.maxVariableCount = settings.maxRoomVariableCount 
 
 newRoom.id = roomManager.roomCounter 
 roomManager.roomCounter ++ 
 
 newRoom.userList = make（[] User，0，newRoom.cappacity）
 newRoom.roomVariables = make（[] RoomVariable，0，newRoom.maxVariableCount） 
 
如果newRoom.InitializeMethod！= nil {
 newRoom.InitializeMethod（arwServer，& newRoom）
} 
 
 roomManager.allRooms = append（roomManager .allRooms，newRoom）
 return& newRoom 
} 
  

将用户添加到房间

  func（room * Room）AddUserToRoom（arwServer * ARWServer，u User）{
 room.userList = append （room.userList，u）
 
 var arwObj ARWObject 
 
 arwObj.requestName = Join_Room 
 arwObj.eventParams.PutString（RoomName，room.name）
 arwObj.eventParams.PutString（RoomTag， room.tag）
 arwObj.eventParams.PutInt（RoomId，room.id）
 arwObj.eventParams.PutInt（RoomCappacity，room.cappacity）
 
 usersData： =
 for ii：= 0; ii< LEN（room.userList）; ii ++ {
 if room.userList [ii] .name！= u.name {
 usersData + = room.userList [ii] .GetDataForOtherUser（u）+''
} 
} 
 
 usersData = strings.TrimRight（usersData，''）
 
 arwObj.eventParams.PutString（Users，usersData）
 arwServer .SendRequestToUser（u，arwObj）
 
 var arwObjforTheOthers ARWObject 
 arwObjforTheOthers.requestName = User_Enter_Room 
 arwObjforTheOthers.eventParams.PutString（RoomName，room.name）
 arwObjforTheOthers .eventParams.PutString（userName，u.name）
 arwObjforTheOthers.eventParams.PutInt（userId，u.id）
 arwObjforTheOthers.eventParams.PutString（isMe，false）
 
 room.SendRequestAllUserWithoutMe（* arwServer，arwObjforTheOthers，u）
 fmt.Println（User join Room  -  User Name：，u.name +Room：+ u.lastRoom.name） 
 
  

解决方案

你的问题是你的结构有非指针切片ES。在所有的结构中，将切片定义为像这样的指针片

 房间[] *房间
  

您还需要定义函数来获取指针值，如

  func（room * Room）{} 
  

详细说明。 Go是传递价值。无论何时，当您从某个原始切片中提取某些内容并将其传递给您的某个函数时，它将获得一份副本。使用指针修改切片中的实际值。

请参阅此示例。 https://play.golang.org/p/ZThHrP0pds

 包主
 
导入（
fmt
）
 
类型结构{
名称字符串
} 
 
 func main（）{
 things：= [] Thing {} 
 thing：= Thing {thing1 } 
 
 //添加到切片
 //注意这是一个函数调用
 things = append（things，thing）
 
 //尝试更改
 thing.Name =thing2
 fmt.Println（things [0] .Name）//打印thing1 
 fmt.Println（thing.Name）//打印thing2 
 
 fmt.Println（------）
 
 //再试一次
 thing3：=东西[0] 
 thing3.Name =thing3
 //再次失败
 fmt.Println（things [0] .Name）//打印thing1 
 fmt.Println（thing3.Name）//打印thing3 
 
 fmt.Println（------）
 
 //代替
 betterThings：= [] * Thing {} //片段指针
 betterThing：=& Thing {thing2} // betterThing是类型* Thing 
 
 //添加到片段
 betterThings = append（betterThings ，betterThing）
 
 //成功更改
 betterThing.Name =thing2
 
 fmt.Println（betterThings [0] .Name）//打印thing2 
 fmt.Println（betterThing.Name）//打印thing2 
} 
  

I'm developing a multiplayer api for Unity Engine. I have Room and RoomManager struct. When I want create room, I set room name, id (all of variable), after that I append this new room to allRoom array in RoomManager struct. After that when I modified to room variable, I can't change any variable. I dont know why ?

Here is my structs and methods :

RoomManager struct

type RoomManager struct {
   allRooms    []Room
   roomCounter int
}

Room struct

type Room struct {
   tag               string
   name              string
   password          string
   id                int
   cappacity         int
   maxVariableCount  int
   userList          []User
   roomVariables     []RoomVariable
   extensionHandlers []ExtensionRequest
   InitializeMethod  roomInitializeFunc
}

Room Create Method

func (roomManager *RoomManager) CreateRoom(settings RoomSettings, arwServer *ARWServer) *Room {

   var newRoom Room
   newRoom.InitializeMethod = settings.InitializeMethod

   newRoom.name = settings.name
   newRoom.password = settings.password
   newRoom.tag = settings.tag
   newRoom.cappacity = settings.cappacity
   newRoom.maxVariableCount = settings.maxRoomVariableCount

   newRoom.id = roomManager.roomCounter
   roomManager.roomCounter++

   newRoom.userList = make([]User, 0, newRoom.cappacity)
   newRoom.roomVariables = make([]RoomVariable, 0, newRoom.maxVariableCount)

   if newRoom.InitializeMethod != nil {
     newRoom.InitializeMethod(arwServer, &newRoom)
   }

   roomManager.allRooms = append(roomManager.allRooms, newRoom)
   return &newRoom
}

Add User To Room

func (room *Room) AddUserToRoom(arwServer *ARWServer, u User) {
   room.userList = append(room.userList, u)

   var arwObj ARWObject

   arwObj.requestName = Join_Room
   arwObj.eventParams.PutString("RoomName", room.name)
   arwObj.eventParams.PutString("RoomTag", room.tag)
   arwObj.eventParams.PutInt("RoomId", room.id)
   arwObj.eventParams.PutInt("RoomCappacity", room.cappacity)

   usersData := ""
   for ii := 0; ii < len(room.userList); ii++ {
     if room.userList[ii].name != u.name {
       usersData += room.userList[ii].GetDataForOtherUser(u) + "''"
     }
   }

   usersData = strings.TrimRight(usersData, "''")

   arwObj.eventParams.PutString("Users", usersData)
   arwServer.SendRequestToUser(u, arwObj)

   var arwObjforTheOthers ARWObject
   arwObjforTheOthers.requestName = User_Enter_Room
   arwObjforTheOthers.eventParams.PutString("RoomName", room.name)
   arwObjforTheOthers.eventParams.PutString("userName", u.name)
   arwObjforTheOthers.eventParams.PutInt("userId", u.id)
   arwObjforTheOthers.eventParams.PutString("isMe", "false")

   room.SendRequestAllUserWithoutMe(*arwServer, arwObjforTheOthers, u)
   fmt.Println("User join Room - User Name : ", u.name+" Room : "+u.lastRoom.name)
}

解决方案

Your issue is that your structs have non-pointer slices. In all of your structs define your slices as slices of pointers like so

Rooms []*Room

You also need to define your functions to take pointer values, like so

func(room *Room) {}

To elaborate. Go is pass-by-value. Anytime you pull something out of one of your original slices and pass it to one of your functions, it gets a copy. Using pointers modifies the actual value in the slice.

See this example. https://play.golang.org/p/ZThHrP0pds

package main

import (
    "fmt"
)

type Thing struct {
    Name string
}

func main() {
    things := []Thing{}
    thing := Thing{"thing1"}

    // add to slice
    // note that this is a function call
    things = append(things, thing)

    // attempt to change
    thing.Name = "thing2"
    fmt.Println(things[0].Name) // prints thing1
    fmt.Println(thing.Name)     // prints thing2

    fmt.Println("------")

    // try again
    thing3 := things[0]
    thing3.Name = "thing3"
    // fail again
    fmt.Println(things[0].Name) // prints thing1
    fmt.Println(thing3.Name)     // prints thing3

    fmt.Println("------")

    // do this instead
    betterThings := []*Thing{} // slice of pointers
    betterThing := &Thing{"thing2"} // betterThing is of type *Thing

    // add to slice
    betterThings = append(betterThings, betterThing)

    // successfully change
    betterThing.Name = "thing2"

    fmt.Println(betterThings[0].Name) // prints thing2
    fmt.Println(betterThing.Name)     // prints thing2
}

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