Develop Reference

How to add a ListBox programmatically in a Form

I started out C# very recently and sorry if this question sounds dumb.
How do I add a Listbox in a Form that pops out from a Button click?
Note: The Form isn't the one that's added from the Solution Explorer whereby I can just drag a Listbox from the Toolbox to my Form.
So what I want is to create a ListBox in my file drawer1Form where I can add additional items. Thanks for the help in advance!:)
private void drawer1button_Click(object sender, EventArgs e) // Drawer 1 Button
{
drawer1Form df1 = new drawer1Form();
df1.StartPosition = FormStartPosition.CenterScreen;
df1.Show();
}
public partial class drawer1Form : Form // Creates drawer1Form
{
public drawer1Form()
{
Text = "Drawer 1 ";
}
}

Pretty much the same way as you'd do with any other object.
In the class of your form add a
private ListBox myAwesomeListBox;
Then in the button event handler add something like this:
myAwesomeListBox = new ListBox();
myAwesomeListBox.SuspendLayout();
// set all the properties that you want
myAwesomeListBox.Name = "myAwesomeListBox";
myAwesomeListBox.Location = new Point(...); // place it somewhere
myAwesomeListBox.Size = new Size(...); // give it a size
// etc...
df1.Controls.Add(myAwesomeListBox);
myAwesomeListBox.ResumeLayout();
This should be it.
I highly advise you to do it through the designer first though, and then take a look at the generated code in the form's .Designer.cs file, you'll have a very good understanding after reading through that.

How to access the Items of a User Control

I have a C# Form that prints multiple instances of a User Control. Let's say that the form prints 5 instances of the User Control (Please see the link attached). How can I store/save the data inputted in all User Controls? Thanks
Here is the screenshot of the C# Form:

You'll have to store the User Controls when you instantiate them in a List or something.
You could have a class like this:
class SomeUC : UserControl
{
public SomeUC()
{
}
// A public method.
public string GetData()
{
return textBox1.Text;
}
}
Where textBox1 is the Name of a TextBox in your SomeUC
And then inside your main or something.
// Instantiate a List that will hold your UserControls, this has to be outside all methods
List<SomeUC> list = new List<SomeUC>();
// And now when you want to build your UCs
// Instantiate your UserControl
SomeUC uc1 = new SomeUC();
// Store your UserControl in a List or something (Can't help you with that)
list.Add(uc1);
Add as much as you want.
A List is not the only way you can do that, but since you don't know how many UserControls you're going to build beforehand, it makes since to use a List.
And then you can access them from the list by their index.
SomeUC uc1 = list[0];
string data = uc1.GetData();
This is an example of accessing one control (the TextBox) in your SomeUC. For other classes (such as the ComboBox) the interaction is different. Meaning you won't have a Text property in the ComboBox. You'll have to figure out things like that on youself. A little research is what it takes. You can always come back if you couldn't find a solution for something.

You can create a property like this for each item in user control.
public string DG
{
get
{
return txtDG.Text;
}
set
{
txtDG.Text = value;
}
}
Then you can access the control value by using following line in your form.
supposed you have created a usercontrol MyControl and you have placed some object of this control in FlowLayoutPenal (pnlFLP).
To get value from control
string DG = ((MyControl)pnlFLP.Controls[0]).DG;
To set value in control
((MyControl)pnlFLP.Controls[0]).DG = "1";

Try this code for accessing user control in the page
Dim txtName As TextBox = TryCast(UserControlName.FindControl("txtName"), TextBox)

The BindingList Datasource of a Combobox refreshes correctly but the Combobox displays items in the wrong order

I have a BindingList< KeyValuePair < string, string > > that is bound to a ComboBox control. Based on some conditions, the BindingList will be added a new KeyValuePair. Now, the Newly added item shows up at index 0 of the Combobox, instead of at the end.
While debugging, I found that the BindingList has got the right order. (i.e, the new KeyValuePair is appended)
Also, I check the SelectedValue of the ComboBox in it's SelectedIndexChanged handler and it seems to be not of the ListItem that got selected. Instead, it is that of the supposed ListItem, if the ComboBox had got the right order as in its DataSource, - the BindingList..
The code is a small part of a large project.. Plz let me know if the question is not clear. I can put the relevant parts of the code as per our context.
How could something like this happen? What can I do differently?
I have this class something like this.
public class DropdownEntity
{
//removed all except one members and properties
private string frontEndName
public string FrontEndName
{
get {return this.frontEndName; }
set {this.frontEndName= value; }
}
//One Constructor
public DropdownEntity(string _frontEndName)
{
this.FrontEndName = _frontEndName;
//Removed code which initializes several members...
}
//All methods removed..
public override string ToString()
{
return frontEndName;
}
}
In my windows form, I have a tab control with several tabs. In one of the tabs pages, I have a DataGridView. The user is supposed to edit the cells and click on a Next - button. Then, some processing will be done, and the TabControl will be navigated to the next tab page.
The next tab page has the combobox that has the problem I mentioned. This page also has a back button, which will take back.. the user can modify the gridview cells again.. and click on the next button. This is when the order gets messed up.
I am posting here the Click event handler of the Next Button.. Along with the class, with the rest of the code removed.
public partial class AddUpdateWizard : Form
{
//Removed all members..
BindingList<KeyValuePair<string, string>> DropdownsCollection;
Dictionary<string, DropdownEntity> DropdownsDict;
//Defined in a partial definition of the class..
DataGridView SPInsertGridView = new DataGridView();
ComboBox DropdownsCmbBox = new ComboBox();
Button NextBtn2 = new Button();
Button BackBtn3 = new Button();
//Of course these controls are added to one of the panels
public AddUpdateWizard(MainForm mainForm)
{
InitializeComponent();
DropdownsDict = new Dictionary<string, DropdownEntity>();
}
private void NextBtn2_Click(object sender, EventArgs e)
{
string sqlArgName;
string frontEndName;
string fieldType;
for (int i = 0; i < SPInsertGridView.Rows.Count; i++)
{
sqlArgName = "";
frontEndName = "";
fieldType = "";
sqlArgName = SPInsertGridView.Rows[i].Cells["InsertArgName"].Value.ToString().Trim();
if (SPInsertGridView.Rows[i].Cells["InsertArgFrontEndName"].Value != null)
{
frontEndName = SPInsertGridView.Rows[i].Cells["InsertArgFrontEndName"].Value.ToString().Trim();
}
if (SPInsertGridView.Rows[i].Cells["InsertArgFieldType"].Value != null)
{
fieldType = SPInsertGridView.Rows[i].Cells["InsertArgFieldType"].Value.ToString().Trim();
}
//I could have used an enum here, but this is better.. for many reasons.
if (fieldType == "DROPDOWN")
{
if (!DropdownsDict.ContainsKey(sqlArgName))
DropdownsDict.Add(sqlArgName, new DropdownEntity(frontEndName));
else
DropdownsDict[sqlArgName].FrontEndName = frontEndName;
}
else
{
if (fieldType == "NONE")
nonFieldCount++;
if (DropdownsDict.ContainsKey(sqlArgName))
{
DropdownsDict.Remove(sqlArgName);
}
}
}
//DropdownsCollection is a BindingList<KeyValuePair<string, string>>.
//key in the BindingList KeyValuePair will be that of the dictionary.
//The value will be from the ToString() function of the object in the Dictionary.
DropdownsCollection = new BindingList<KeyValuePair<string,string>>(DropdownsDict.Select(kvp => new KeyValuePair<string, string>(kvp.Key, kvp.Value.ToString())).ToList());
DropdownsCmbBox.DataSource = DropdownsCollection;
DropdownsCmbBox.DisplayMember = "Value";
DropdownsCmbBox.ValueMember = "Key";
//Go to the next tab
hiddenVirtualTabs1.SelectedIndex++;
}
private void BackBtn3_Click(object sender, EventArgs e)
{
hiddenVirtualTabs1.SelectedIndex--;
}
//On Selected Index Changed of the mentioned Combobox..
private void DropdownsCmbBox_SelectedIndexChanged(object sender, EventArgs e)
{
if (DropdownsCmbBox.SelectedValue != null)
{
if (DropdownsDict.ContainsKey((DropdownsCmbBox.SelectedValue.ToString())))
{
var dropdownEntity = DropdownsDict[DropdownsCmbBox.SelectedValue.ToString()];
DropdownEntityGB.Text = "Populate Dropdowns - " + dropdownEntity.ToString();
//Rest of the code here..
//I see that the Datasource of this ComboBox has got the items in the right order.
// The Combobox's SelectedValue is not that of the selected item. Very Strange behavior!!
}
}
}
}
The very first time the user clicks the Next Button, it's fine. But if he clicks the Back Button again and changes the Data Grid View cells.. The order will be gone.
I know, it can be frustrating to look at. It's a huge thing to ask for help. Any help would be greatly appreciated!
Please let me know if you need elaboration at any part.
Thanks a lot :)

I think you have two problems here.
First, if you want to retain the order of the items you should use an OrderedDictionary instead of a regular one. A normal collection will not retain the order of the items when you use Remove method. You can see more info about this related to List here.
You could use such dictionary like this:
DropDownDict = new OrderedDictionary();
// Add method will work as expected (as you have it now)
// Below you have to cast it before using Select
DropDownCollection = new BindingList<KeyValuePair<string, string>>(DropDownDict.Cast<DictionaryEntry>().Select(kvp => new KeyValuePair<string, string>(kvp.Key.ToString(), kvp.Value.ToString())).ToList());
The second problem could be that you change the display name (FrontEndName) of already existing items, but the key is preserved. When you add a new item, try to remove the old one that you're not using anymore and add a new item.

The Sorted Property of the Combobox is set to True! I didn't check that until now. I messed up. Terribly sorry for wasting your time Adrian. Thanks a lot for putting up with my mess here.. :)

Two comboBoxes with same members, when one selected, other must be unable to select same member

So I have two comboBoxes (comboBoxFromAccount and comboBoxToAccount). Each has the same datasource, which is AccountsList (a list of BankAccount objects that was passed from the parent form).
I would like to make it so that if an item is selected in one of the comboBoxes, it would no longer be selectable in the other. The way I'm trying to do this is by copying the list of BankAccounts from the comboBoxFromAccount to the comboBoxTo account, and removing the selected index of comboBoxFromAccount from the comboBoxToAccount.
I think I'm close, but what seems to happen is I have a blank comboBoxToAccount.
Here is my code:
private BankAccountCollection accountsListTransferTo = new BankAccountCollection();
// public property for passing collection data to the dialog
public BankAccountCollection AccountsList
{
get { return accountsListTransferTo; }
set { accountsListTransferTo = value; }
}
// Initial loading
private void TransferFundsDialog_Load(object sender, EventArgs e)
{
textBoxAmount.Text = String.Empty;
textBoxAmount.Select();
comboBoxFromAccount.DataSource = AccountsList;
accountsListTransferTo.AddRange(AccountsList); // Copy content
accountsListTransferTo.Remove(comboBoxFromAccount.SelectedItem as BankAccount); // Remove item
comboBoxToAccount.DataSource = accountsListTransferTo; // Data binding
}
private void comboBoxFromAccount_SelectedIndexChanged(object sender, EventArgs e)
{
accountsListTransferTo.Clear(); // Clear list, if you don't to it, AddRange will just add more items.
accountsListTransferTo.AddRange(AccountsList); // Copy ALL accounts
accountsListTransferTo.Remove(comboBoxFromAccount.SelectedItem as BankAccount); // Remove selected, so user cannot transfer to same account
// Refresh data binding
comboBoxToAccount.DataSource = null;
comboBoxToAccount.DataSource = accountsListTransferTo;
// Select very first item in "TO" combobox
comboBoxToAccount.SelectedIndex = 0;
}
Help would be appreciated.

Try removing the line
comboBoxToAccount.DataSource = null;
I have a vague recollection about comboboxes having problems with this.

Another possible problem that I can see is that you are using accountsListTransferTo both as your master collection and the one where you are removing the selected account from. Every time comboBoxFromAccount_SelectedIndexChanged is called one more account will disappear from the collection (and therefore from the available options in comboBoxToAccount).
I think I have seen comboboxes behave in a way where the SelectedIndexChanged (or a similar) event is triggered as new items are being added. If that is the case here it will explain the empty comboBoxToAccount, because comboBoxFromAccount_SelectedIndexChanged will run once for each bank account being added, essentially removing them from the master list and then rebinding the reduced list. You can easily verify this with a break point in your event handler.

Using a class initiated in one method in another method

I have a C# WPF app that every time the user opens a new file, the contents are displayed in a datagrid.
public partial class MainWindow : Window
{
public TabControl tc = new TabControl();
public MainWindow()
{
InitializeComponents();
}
private FromFile_click(object sender, RoutedEventArgs e)
{
//gets information from file and then...
if (numberOfFiles == 0)
{
masterGrid.Children.Add(tc);
}
TabItem ti = new TabItem();
tc.Items.Add(ti);
DataGrid dg = new DataGrid();
ti.Content = dg;
dg.Name = "Grid"+ ++numberOfFiles;
dg.ItemSource = data;
}
private otherMethod(object sender, RoutedEventArgs e)
{
}
}
My question is, how do I use the data in dg in the method "otherMethod"? Also, is it possible to change the parent of dg from the method "otherMethod"?

Assuming you're not calling otherMethod within FromFile_Click, you need to make it an instance variable - like your TabControl is, except hopefully not public. I'm assuming otherMethod is actually meant to handle an event of some kind, rather than being called directly.
Now this is assuming that you want one DataGrid per instance of MainWindow, associated with that window. If that's not the case, you'd need to provide more information.

You have to pass it as a parameter to the other method otherMethod or make it a member variable.

set the DataGrid dg as a property instead of declaring inside the FromFile_click.
This way when you assign "dg" it will work from any other method (few restrictions apply)