设置器在模型中不起作用[重复]

Question

This question already has an answer here:

• Using a setter for a struct type does not work as anticipated 2 answers

I am making this code trying to understand the MVC architecture while learning Go, and I am stuck trying to change values in the model from the controller.

The code right now creates a model that only holds a string, the view shows that string on the terminal, but the controller can not change it (it gets the user input without any problem).

Right now the text I get in the terminal is like this:

Hello World!
asdf //my input
Hello World!

And the output I would like to get would be like this:

Hello World!
asdf //my input
asdf

Here are my files:

model.go

package models

type IndexModel struct {
    Text string
}

func (m *IndexModel) InitModel() string {
    return m.Text
}

func (m *IndexModel) SetText(newText string) {
    m.Text = newText
}

view.go

package views

import "github.com/jufracaqui/mvc_template/app/models"

type IndexView struct {
    Model    models.IndexModel
}

func (v IndexView) Output() string {
    return v.Model.Text
}

controller.go

package controllers

import "github.com/jufracaqui/mvc_template/app/models"

type IndexController struct {
    Model models.IndexModel
}

func (c IndexController) ChangeText(userInput string) {
    c.Model.SetText(userInput)
}

main.go:

package main

import (
    "bufio"
    "os"

    "fmt"

    "github.com/jufracaqui/mvc_template/app/controllers"
    "github.com/jufracaqui/mvc_template/app/models"
    "github.com/jufracaqui/mvc_template/app/views"
)

func main() {
    handleIndex()
}

func handleIndex() {
    model := models.IndexModel{
        "Hello World!",
    }

    controller := controllers.IndexController{
        model,
    }

    viewIndex := views.IndexView{
        model,
    }

    fmt.Println(viewIndex.Model.Text)

    reader := bufio.NewReader(os.Stdin)
    text, _ := reader.ReadString('
')
    controller.ChangeText(text)
    fmt.Println(viewIndex.Model.Text)
}

Edit: How my code ended up after @JimB answer:

model.go:

package models

type IndexModel struct {
    Text string
}

func (m *IndexModel) InitModel() string {
    return m.Text
}

view.go:

package views

import "github.com/jufracaqui/mvc_template/app/models"

type IndexView struct {
    Model    *models.IndexModel
}

func (v IndexView) Output() string {
    return v.Model.Text
}

controller.go:

package controllers

import "github.com/jufracaqui/mvc_template/app/models"

type IndexController struct {
    Model *models.IndexModel
}

func (c IndexController) ChangeText(userInput string) {
    c.Model.Text = userImput
}

main.go:

package main

import (
    "bufio"
    "os"

    "fmt"

    "github.com/jufracaqui/mvc_template/app/controllers"
    "github.com/jufracaqui/mvc_template/app/models"
    "github.com/jufracaqui/mvc_template/app/views"
)

func main() {
    handleIndex()
}

func handleIndex() {
    model := models.IndexModel{
        "Hello World!",
    }

    m := &model

    controller := controllers.IndexController{
        m,
    }

    viewIndex := views.IndexView{
        m,
    }

    fmt.Println(viewIndex.Model.Text)

    reader := bufio.NewReader(os.Stdin)
    text, _ := reader.ReadString('
')
    controller.ChangeText(text)
    fmt.Println(viewIndex.Model.Text)
}

</div>

Answer 1

IndexController.ChangeText needs a pointer receiver, or IndexController.Model needs to be a pointer. You're calling SetText on a copy of the SetText value.

If you expect things to be mutable, it's much easier to consistently use pointers to structs throughout, and make explicit struct values the exception when you really need them.