I know how to send information from Form1 to Form2, but how do I edit it and send it back if the data is contained in a List in Form1?

问题

I have this code to send it from Form1 to Form2:

public partial class Form1 : Form
{
    public ShoppingBasket myBasket = new ShoppingBasket();

    public Form1()
    {
        InitializeComponent();
    }

    private void editButton_Click(object sender, EventArgs e)
    {
        int c = lstCart.Items.Count - 1;

        for (int i = c; i <= 0; i++)
        {
            if (lstCart.GetSelected(i))
            {
                Form2 fm2 = new Form2();
                fm2.productNameTextBox.Text = myBasket[i].ProductName;
                fm2.quantityTextBox.Text = Convert.ToString(myBasket[i].Quantity);
                fm2.latestPriceTextBox.Text = Convert.ToString(myBasket[i].LatestPrice);
                fm2.ShowDialog();
            }
        }
    }
}

Then this is my Form2 code:

public partial class Form2 : Form
{
    public Form2()
    {
        InitializeComponent();
    }
    Form1 fm1 = new Form1();

    private void okBtn_Click(object sender, EventArgs e)
    {
        int c = fm1.lstCart.Items.Count - 1;

        for (int i = c; i <= 0; i++)
        {
            if (this.fm1.lstCart.GetSelected(i))
            {
                this.fm1.myBasket[i].ProductName = this.productNameTextBox.Text;
                this.fm1.myBasket[i].Quantity = Convert.ToInt32(this.quantityTextBox.Text);
                this.fm1.myBasket[i].LatestPrice = Convert.ToDecimal(this.latestPriceTextBox.Text);
                this.Close();
            }
        }
    }

    private void cancelBtn_Click(object sender, EventArgs e)
    {
        this.Close();
    }
}

This is my ShoppingBasket class:

public class ShoppingBasket : List<OrderItem>
{
    public ShoppingBasket()
    {

    }

    public decimal BasketTotal { get; set; }

    public new void Add(OrderItem i)
    {
        base.Add(i);
    }

    public new void Remove(OrderItem i)
    {
        base.Remove(i);
    }

OrderItem class:

public class OrderItem
{
    public OrderItem(string productName, 
    decimal latestPrice, int quantity)
    {
        ProductName = productName;
        LatestPrice = latestPrice;
        Quantity = quantity;
        TotalOrder = latestPrice * quantity;
    }

    public string ProductName { get; set; }

    public decimal LatestPrice { get; set; }

    public int Quantity { get; set; }

    public decimal TotalOrder { get; set; }
}

The problem I am getting is that it gives me: 'ArgumentOutOfRangeException was unhandled' saying "Index -1 is out of range. Parameter name: index" pointing to this line: if (this.fm1.lstCart.GetSelected(i))

But previously it has given me another error saying "Object reference not set to an instance of an object."

How do I make it so that the values previously in the selected field in Form1 are changed to the values I pass from Form2 back to Form1?

回答1:

When you make new Form1() inside Form2, you are creating a completely new Form1 with no filled data. It's not the original Form1 that called Form2.

So, what you need is to set that Form1 to the original, not to a new one:

public partial class Form2 : Form
{
    public Form2()
    {
        InitializeComponent();
    }

    public Form1 fm1; //just declare, but let Form1 do the assign job.

    //the rest of the code...
}

And in Form 1

for (int i = c; i <= 0; i++)
{
    if (lstCart.GetSelected(i))
    {
        Form2 fm2 = new Form2();
        fm2.productNameTextBox.Text = myBasket[i].ProductName;
        fm2.quantityTextBox.Text = Convert.ToString(myBasket[i].Quantity);
        fm2.latestPriceTextBox.Text = Convert.ToString(myBasket[i].LatestPrice);

        //here is the news:
        fm2.fm1 = this;

        fm2.ShowDialog();
    }
}

回答2:

As daniel mentioned you need to pass a reference to your form1 into form2, personally I'd do it in a constructor

public Form2(Form1 form)
{
    fm1 = form;
}

Then you really should try to only update a forms fields within the form itself whereever possible so since form2 is modal I'd do something similar to this

using(Form2 fm2 = new Form2(this))
{
    fm2.productNameTextBox.Text = myBasket[i].ProductName;
    fm2.quantityTextBox.Text = Convert.ToString(myBasket[i].Quantity);
    fm2.latestPriceTextBox.Text = Convert.ToString(myBasket[i].LatestPrice);
    if(DialogResult.OK == fm2.ShowDialog(this))
    {
        myBasket[i].ProductName = frm2.productNameTextBox.Text;
        myBasket[i].Quantity = Convert.ToInt32(frm2.quantityTextBox.Text);
        myBasket[i].LatestPrice = Convert.ToDecimal(frm2.latestPriceTextBox.Text);
    }
}

then to close form2 use