Combobox SelectedItem not working propely

Question

I'm trying to retrieve the selected item from a combobox, though i can't get it to work.

Form1 form = new Form1();
string cpuCount = form.comboBox1.SelectedItem.ToString();

Now, this is not returning anything. BUT, if i insert this code in my InitializeComponent(), it selects item with index = 3, and return that proper item.

comboBox1.SelectedIndex = 3;

Why does it behave like this? If I now select for example item with index = 5, it still will think the selected item is the one with index = 3.

---------- I think i should expand to show you how my code looks.

Form1 - adding all items to the comboboxes.

public partial class Form1 : Form
{
    Profile profile = new Profile();
    public Form1()
    {
        InitializeComponent();
        Profile profile = new Profile();
        string[] prof = profile.getProfiles();
        foreach (var item in prof)
        {
            comboBox5.Items.Add(Path.GetFileNameWithoutExtension(item));
        }

        int ram = 1024;
        for (int i = 0; i < 7; i++)
        {
            comboBox4.Items.Add(ram + " GB");
            ram = ram * 2;
        }

        int vram = 512;
        string size;
        for (int i = 0; i < 5; i++)
        {
            if(vram > 1000)
            {
                size = " GB";
            }
            else
            {
                size = " MB";
            }
            comboBox2.Items.Add(vram + size);
            vram = vram * 2;
        }

        for (int i = 1; i < 5; i++)
        {
            comboBox1.Items.Add(i * 2);
        }

        for (int i = 0; i < 5; i++)
        {
            comboBox3.Items.Add(i * 2);
        }

        private void button3_Click(object sender, EventArgs e)
        {
            string current = profile.currentProfile();
            profile.saveProfile(current);
        }

    }

So, button3 is my "save"button. And here is my "Profile"-class

class Profile
{
    public string folder { get; set; }
    public Profile()
    {
        this.folder = "Profiles";
        if (!File.Exists(folder))
        {
            Directory.CreateDirectory(folder);
            File.Create(folder + "/default.cfg").Close();
        }
    }

    public string[] getProfiles()
    {
        string[] files = Directory.GetFiles(folder);
        return files;
    }

    public void saveProfile(string filename)
    {
        Form1 form = new Form1();
        string cpuCount = "cpuCount=" + form.comboBox1.SelectedItem;
        string RAM = "maxRAM=" + form.comboBox4.SelectedItem;
        string VRAM = "maxVRAM=" + form.comboBox2.SelectedItem;
        string threads = "cpuThreads=" + form.comboBox3.SelectedItem;
        string path = folder + "/" + filename;
        StreamWriter sw = new StreamWriter(path);
        string[] lines = { cpuCount, RAM, VRAM, threads };

        foreach (var item in lines)
        {
            sw.WriteLine(item);
        }



        sw.Close();

    }

    public string currentProfile()
    {
        Form1 form = new Form1();
        string selected = form.comboBox5.SelectedValue + ".cfg".ToString();
        return selected;
    }
}

Thank you.

Answer 1

The problem is that there is nothing selected in your ComboBox. You create your form and then, without previous user interaction, you want to get the SelectedItem which is null at that moment.

When you create ComboBox control and fill it with items, SelectedItem property is null until you either programratically set it (by using for example comboBox1.SelectedIndex = 3) or by user interaction with the control. In this case you are not doing anything of the above and that is why you are geting the mentioned error.

EDIT Based on the edited question Change your code like this: first change the saveProfile method so you could pass the four strings which you write into the text file. Note that you could alternatively pass the reference of the form but I wouldn't suggest you that. So change the method like this:

public void saveProfile(string filename, string cpuCount, string RAM , string VRAM , string threads)
    {
        string path = folder + "/" + filename;
        using(StreamWriter sw = new StreamWriter(path)) 
        {
             sw.WriteLine("cpuCount=" + cpuCount);
             sw.WriteLine("maxRAM=" + RAM );
             sw.WriteLine("maxVRAM=" + VRAM );
             sw.WriteLine("cpuThreads=" + threads);
        }        
    }

And then call it from button3 Click event handler like this:

private void button3_Click(object sender, EventArgs e)
{
            string current = profile.currentProfile();
            string cpuCount = this.comboBox1.SelectedItem.ToString();
            string RAM =  this.comboBox4.SelectedItem.ToString();
            string VRAM = this.comboBox2.SelectedItem.ToString();
            string threads = this.comboBox3.SelectedItem().ToString();
            profile.saveProfile(current, cpuCount, RAM, VRAM, threads);
}

Or alternatively

private void button3_Click(object sender, EventArgs e)
{
            string current = profile.currentProfile();
            profile.saveProfile(current, this.comboBox1.SelectedItem.ToString(), this.comboBox4.SelectedItem.ToString(), this.comboBox2.SelectedItem.ToString(), this.comboBox3.SelectedItem().ToString());
}

Answer 2

First of all, add a Form_Load Event and put your code in the handler. (use constructor for property initialization and other variable initialization)

private void Form1_Load(object sender, EventArgs e)
{
this.comboBox1.SelectedItem= 5; // This will set the combo box to index 5
string cpuCount = this.comboBox1.SelectedText; // This will get the text of the selected item
}

so you get the value of item at index 5 in cpuCount variable.

The selected clause gives you the values AFTER you have selected something, by default(when you run your app) there is nothing selected in the comoboBox, hence, it displays the value as null, after selecting the item you can use the combobox's selectedItem, selectedIndex, selectedText and selectedValue properties.

You can also use databinding to display items in the combobox, which in my view is a better way then adding the items manually.

to databind your combobox you can use,

// Bind your combobox to a datasource, datasource can be a from a database table, List, Dataset, etc..

 IDictionary<int, string> comboDictionary = new Dictionary<int, string>();
            comboDictionary.Add(1, "first");
            comboDictionary.Add(2, "second");
            comboDictionary.Add(3, "third");
            comboBox1.DataSource = comboDictionary;
            comboBox1.DisplayMember = "Key";
            comboBox1.ValueMember = "Value";

// 

And here now you can use combobox1.SelectedIndex to go through the item collection in the datasource :) and it will give you the value against your keys when you use combobox1.SelectedValue. Hope this helps.

Answer 3

Your ComoboBox doesn't have items in it. So it will not return properly. You are accessing combobox selected value rights after making form object.

And if it comboBox has items then nothing is being selected. By default nothing is selected in comboBox. You need to set it. Use this. What it returns? Set comboBox.SelectedIndex and then get selectedItem.

int selectedIndex = form.comboBox1.SelectedIndex;

Try this. Add some items in ComboBox and then get selectedItem.

Form1 form = new Form1();
form.comboBox1.Add("Item 1");
form.comboBox1.Add("Item 2");
form.comboBox1.Add("Item 3");
form.comboBox1.SelectedIndex = 1;
string cpuCount = form.comboBox1.SelectedItem.ToString();

Answer 4

From what I can see, you are calling form.comboBox1.SelectedItem.ToString() right after the creation of Form1. This means that the cpuCount variable is initialized right after the form is created, thus far before you have the chance to change the selected item with your mouse.

If you want to retrieve the value of the combobox after it is changed, you can use the SelectedIndexChanged event.