无法将selectedItem获取到文本框

Question

I'm trying to get listbox selected item from one form 1 to display on textbox on form 2.

So far it's working partly.

The problem is that it only gets the selectedItem that was selected at the start of the application. If the user selects a new item, it still gets the one that was selected as default.

Form 1 MainForm :

public MainForm()
{
    public string GetListBoxSelectedItem()
    {
        if (Animallst.SelectedItem != null) //Animallst is the listbox
        {
            return Animallst.SelectedItem.ToString();
            return string.Empty;
        }
    }

    private void foodbtn_Click(object sender, EventArgs e)
    {
        FoodRegister foodForm = new FoodRegister();
        foodForm.Show();
    }
}

Form 2 FoodRegister :

public partial class FoodRegister : Form
{
    private RecipeManager m_foodmanager = new RecipeManager();

    public FoodRegister() 
    {
        InitializeComponent();

        MainForm main = new MainForm();
        Nametxt.Text = main.GetListBoxSelectedItem();
        //My initializations
        InitializeGUI();
    }
}

Answer 1

These two lines are not at all doing what you want them to do. You're creating an entirely new instance of MainForm , which has nothing to do with the original instance. And so GetListBoxSelectedItem() doesn't do what you want either.

MainForm main = new MainForm();
Nametxt.Text = main.GetListBoxSelectedItem();

Instead, pass a reference to the original Form into the second Form:

public FoodRegister(MainForm main) 
{
    InitializeComponent();

    Nametxt.Text = main.GetListBoxSelectedItem();
    ...

And then call it like this:

FoodRegister foodForm = new FoodRegister(this);
foodForm.Show();

Answer 2

A couple of things to mention:

1. The line return string.Empty is redundant. Because of the line above it, this line becomes unreachable

2. In your FoodRegister for, you create a new instance of your main form. This then wipes anything that the main form was holding - ie Animallst.SelectedItem.ToString();

An easy way to handle this is to set the value to a static variable - that way you won't have to create a new instance of the form to access it.

Main form:

public static string GetListBoxSelectedItem()
{
    if (Animallst.SelectedItem != null) //Animallst is the listbox
    {
        return Animallst.SelectedItem.ToString();
    }
    else { return string.Empty(); }
}

Food Register:

public FoodRegister() 
{
    InitializeComponent();

    MainForm.GetListBoxSelectedItem();
    //My initializations
    InitializeGUI();
}

Answer 3

Haven't played with WinForms in awhile but here goes In Form 2

public partial class FoodRegister : Form
{
    private RecipeManager m_foodmanager = new RecipeManager();
    public FoodRegister() 
    {
        InitializeComponent();
        //My initializations
        InitializeGUI();
    }
    public void SetText(string txt)
    {
         Nametxt.Text = txt;
    }
}

In Form 1

public MainForm()
{
    private readonly FoodRegister foodForm = new FoodRegister();

    private void foodbtn_Click(object sender, EventArgs e)
    {
        foodForm.SetText(Animallst.SelectedItem == null ? "" : Animallst.SelectedItem.ToString());
        foodForm.Show();
    }
}

I replaced

GetListBoxSelectedItem()

with

Animallst.SelectedItem == null ? "" : Animallst.SelectedItem.ToString()