CODEWITHSUNDEEP
c#visual-studio-2015listbox
Jonathan Fogelström
Jonathan Fogelström

Reputation: 33

ListBox causes program to crash when clicking in an empty area

I'm creating a flip card program that lets you insert a word and it's description. The word is added to a ListBox whilst the description is held in a string array. I've told the program to find the correct description once a ListBox item is clicked as shown in the code below. although this causes the program to crash if the user clicks on an empty area in the ListBox. How can I get around this?

public partial class Form1 : Form
{
    int i = 0;
    string[] details = new string[20];

    private void insertbtn_Click(object sender, EventArgs e)
    {
        listBox1.Items.Add(inserttbx.Text); //Adds word to the ListBox
    }

    private void editDescbtn_Click(object sender, EventArgs e)
    {
        details[i] = descriptiontbx.Text; //adds text from descriptiontbx to "details" array
        i++;
    }

    private void listBox1_Click(object sender, EventArgs e)
    {
        if(i == 0) //int i equals the amount of items in the ListBox.
        {

        }
        else
        {
            int b = listBox1.SelectedIndex;
            descriptiontbx.Text = details[b]; 
            //"details" string array, will open the correct description
            //depending on which ListBox item is selected.
        }
    }
}

Diagram of my program

Translations:

Infoga: Insert
Redigera: Edit

Note that all the functions in the program are not included in the code!

Upvotes: 1

Views: 671

Answers (1)

ChrisF
ChrisF

Reputation: 137148

ListBox.SelectedIndex is:

A zero-based index of the currently selected item. A value of negative one (-1) is returned if no item is selected

Source

Therefore if no item is selected:

        int b = listBox1.SelectedIndex;
        descriptiontbx.Text = details[b];

will cause the crash as b is -1, which is out of range for an array. Add a check to make sure that SelectedIndex >= 0 before trying to use the value.

Upvotes: 1

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