Go Reflect 方法调用无效的内存地址或 nil 指针取消引用

Question

我正在尝试使用反射来调用结构上的方法。但是，即使 attachMethodValue 和 args 都不为零，我也会得到 panic: runtime error: invalid memory address or nil pointer dereference。关于它可能是什么的任何想法？

去游乐场：http://play.golang.org/p/QSVTSkNKam

package main

import "fmt"
import "reflect"

type UserController struct {
    UserModel *UserModel
}

type UserModel struct {
    Model
}

type Model struct {
    transactionService *TransactionService
}

func (m *Model) Attach(transactionService *TransactionService) {
    m.transactionService = transactionService
}

type Transactioner interface {
    Attach(transactionService *TransactionService)
}

type TransactionService struct {
}

func main() {
    c := &UserController{}
    transactionService := &TransactionService{}
    valueField := reflect.ValueOf(c).Elem().Field(0) // Should be UserController.UserModel

    // Trying to call this
    attachMethodValue := valueField.MethodByName("Attach")

    // Argument
    args := []reflect.Value{reflect.ValueOf(transactionService)}

    // They're both non-nil
    fmt.Printf("%+v\n", attachMethodValue)
    fmt.Println(args)

    // PANIC!
    attachMethodValue.Call(args)

    fmt.Println("The end.")
}

Answer 1

由于 UserModel 指针为 nil，它出现了混乱。我想你想要：

c := &UserController{UserModel: &UserModel{}}

playground example

Go Reflect 方法调用无效的内存地址或 nil 指针取消引用

Go Reflect Method Call invalid memory address or nil pointer dereference

reflection

go