C# WinForms - Clearing the list of items in ListBox when DataBinding to a Dictionary

Hi,

try lbxSelectedLocations.Items.clear()

Thanks roxviper,

That doesn't work becuase the listbox has been databind and it throws an exception, the Items can't be cleared because of the databind.

http://support.microsoft.com/kb/319927

Ok, So I tried setting the DataSource = null, the problem is that after that is done, when I try to bind it again the ListBox doesn't display anything

https://www.experts-exchange.com/questions/24098833/Comboxbox-Listbox-WPF-DataBinding-Issues.html

Sorry, I didn't mention that I'm looking for a .net 2.0 solution

I don't understand the problem here.. This is a simple example, and it sets/resets the data source for listbox without any problem. Can you please exaplin better where the problem is:

private void btAdd_Click(object sender, EventArgs e)
{
    Dictionary<int, string> list = new Dictionary<int, string>();

    list.Add(0, "a");
    list.Add(1, "b");
    list.Add(2, "c");

    listBox1.DataSource = new BindingSource(list, null);
    listBox1.DisplayMember = "Value";
    listBox1.ValueMember = "Key";

}

private void btnRemove_Click(object sender, EventArgs e)
{
    listBox1.DataSource = null;
}

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Priest04,

After the DataSource has been set to null, the next time I go to set the DataSource with a new list of selectedOptions, the ListBox doesn't show the new list.

What if you bind an empty list exactly the way you do with the above one?


    Dictionary<int, string> list = new Dictionary<int, string>();
    listBox1.DataSource = new BindingSource(list, null);
    listBox1.DisplayMember = "Value";
    listBox1.ValueMember = "Key";

It throws an exception when I try to bind an empty list to it

But if try simple example I gave above, you click btnAdd to set Datasrouce, then you click btnRemove to set datasource to null, and then again btnAdd to set it again, and no problem occur. So, it is not a problem with actual binding?

Hi Priest04,

After setting the datasource to null, and then when I tried adding it again - the Listbox doesn't show anything - it stays empty and doesn't show anything.

Q-M, its important to understand this: is this happening with your code, or mine?

I 've gone and changed my lines of code from:

lbxSelectedCourses.DataBindings.Clear();  
to
lbxSelectedCourses.DataSource = null;

Try to run it, and after I set the DataSource to null, I tried binding a new Dictionary list that has items in it, and the listbox didn't show anything.

Ok, but first we need to clear something - this is not a problem with actual databinding. This I say because, if you just paste my code into new project, you will see that it works flawlessly. So the problem is proably somewhere else, you have several if and switch statements, so maybe the problem is with them. You need to put some breakpoint and see what part of code will run, check if Dictionary actually has items in it...

After debugging and adding breakpoints in my code, I can verify that everything is working fine with all the switch statements I have in my code.

I did notice that after setting lbxSelectedLocations.DataSource = null; to the Locations listbox
I added the following code:
foreach (KeyValuePair<int, string> selItem in lbxSelectedLocations.Items)
{
         MessageBox.Show(selItem.Value);
}

And it popped up with the list of listbox items, even though I set the datasource to null.

case PublicEvaluationReportSearchOptions.Locations:
	lbxSelectedLocations.DataSource = null;
	foreach (KeyValuePair<int, string> selItem in lbxSelectedLocations.Items)
	{
	    MessageBox.Show(selItem.Value);
	}
	break;

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Can you please post the complete code here, so we can test this?

Ok here is the main form where I display the listboxes

public partial class PublicCourseEvaluationReport : System.Windows.Forms.Form
    {        
        public PublicCourseEvaluationReport()
        {
            InitializeComponent();            
        }

        public void LoadThisForm()
        {
            InitializeDataGridView();
            this.MdiParent = ApplicationForms.MainFormRef;
            this.Show();
        }

        private void InitializeDataGridView()
        {
            //Get XML Style template from DB
            dvgEvaluationResults.Columns.Clear();
            WebValues wbTemplate = WebValues.GetWebValue("PublicCourseEvalDisplayTemplate");
            if (string.IsNullOrEmpty(wbTemplate.WebVal_Value))
            {
                //Load these default settings
                //Set the selection background color for all the cells in Master Grid
                dvgEvaluationResults.DefaultCellStyle.SelectionBackColor = ColorTranslator.FromHtml("#0054E3");
                dvgEvaluationResults.DefaultCellStyle.SelectionForeColor = ColorTranslator.FromHtml("#000000");

                //Set RowHeadersDefaultCellStyle.SelectionBackColor so that its default
                //value won't override DataGridView.DefaultCellStyle.SelectionBackColor.
                dvgEvaluationResults.RowHeadersDefaultCellStyle.SelectionBackColor = Color.Empty;

                //Set Row Styles
                dvgEvaluationResults.RowsDefaultCellStyle.BackColor = ColorTranslator.FromHtml("#FFFFFF");
                dvgEvaluationResults.AlternatingRowsDefaultCellStyle.BackColor = ColorTranslator.FromHtml("#D5DEE1");

                //Set Column Header Style
                DataGridViewCellStyle headerCellStyle = new DataGridViewCellStyle();
                headerCellStyle.BackColor = ColorTranslator.FromHtml("#577B87");
                headerCellStyle.ForeColor = ColorTranslator.FromHtml("#FFFFFF");
                using (Font fnt = new Font("Verdana", 8))
                {
                    headerCellStyle.Font = fnt;
                }
                dvgEvaluationResults.ColumnHeadersDefaultCellStyle = headerCellStyle;
            }
            //else
            //{
            //    //Go through the XML Template and set the datagrid settings
            //    string cellStyle = "";
            //}

            //Add Columns to DataGrid
            DataGridViewColumn column;
            column = new DataGridViewTextBoxColumn();
            column.Name = "Evnt_ID";
            column.HeaderText = "Event ID";
            column.Width = 80;
            dvgEvaluationResults.Columns.Add(column);

            column = new DataGridViewTextBoxColumn();
            column.Name = "Evnt_Dates";
            column.HeaderText = "Event Dates";
            column.Width = 120;
            dvgEvaluationResults.Columns.Add(column);

            column = new DataGridViewTextBoxColumn();
            column.Name = "Course_Title";
            column.HeaderText = "Course Title";
            column.Width = 400;
            dvgEvaluationResults.Columns.Add(column);

            column = new DataGridViewTextBoxColumn();
            column.Name = "Location";
            column.HeaderText = "Location";
            column.Width = 100;
            dvgEvaluationResults.Columns.Add(column);

            column = new DataGridViewTextBoxColumn();
            column.Name = "Venue";
            column.HeaderText = "Venue";
            column.Width = 250;
            dvgEvaluationResults.Columns.Add(column);

            column = new DataGridViewTextBoxColumn();
            column.Name = "Instructors";
            column.HeaderText = "Instructor(s)";
            column.Width = 150;
            dvgEvaluationResults.Columns.Add(column);

            column = new DataGridViewTextBoxColumn();
            column.Name = "Date_Submitted";
            column.HeaderText = "Date Submitted";
            column.Width = 120;
            dvgEvaluationResults.Columns.Add(column);

            column = new DataGridViewTextBoxColumn();
            column.Name = "Participant_Name";
            column.HeaderText = "Participant Name";
            column.Width = 150;
            dvgEvaluationResults.Columns.Add(column);

            column = new DataGridViewTextBoxColumn();
            column.Name = "Company";
            column.HeaderText = "Company";
            column.Width = 250;
            dvgEvaluationResults.Columns.Add(column);

            column = new DataGridViewTextBoxColumn();
            column.Name = "Question_Number";
            column.HeaderText = "#";
            column.Width = 30;
            dvgEvaluationResults.Columns.Add(column);

            column = new DataGridViewTextBoxColumn();
            column.Name = "Question_Text";
            column.HeaderText = "Question Text";
            column.Width = 400;
            dvgEvaluationResults.Columns.Add(column);

            column = new DataGridViewTextBoxColumn();
            column.Name = "Question_Answer";
            column.HeaderText = "Question Answer";
            column.Width = 150;
            dvgEvaluationResults.Columns.Add(column);

            column = new DataGridViewTextBoxColumn();
            column.Name = "Question_Comment";
            column.HeaderText = "Question Comment";
            column.Width = 450;
            dvgEvaluationResults.Columns.Add(column);

            column = new DataGridViewTextBoxColumn();
            column.Name = "InHouse_Reference";
            column.HeaderText = "InHouse Reference";
            column.Width = 200;
            dvgEvaluationResults.Columns.Add(column);
        }

        public void UpdateSearchItems(PublicEvaluationReportSearchOptions searchOption, Dictionary<int, string> selectedOptions)
        {
            //Only add items when the user has made selections
            if (selectedOptions.Count > 0)
            {
                switch (searchOption)
                {
                    case PublicEvaluationReportSearchOptions.Courses:
                        lbxSelectedCourses.DataSource = new BindingSource(selectedOptions, null);
                        lbxSelectedCourses.DisplayMember = "Value";
                        lbxSelectedCourses.ValueMember = "Key";
                        break;
                    case PublicEvaluationReportSearchOptions.Events:
                        lbxSelectedEvents.DataSource = new BindingSource(selectedOptions, null);
                        lbxSelectedEvents.DisplayMember = "Value";
                        lbxSelectedEvents.ValueMember = "Key";
                        break;
                    case PublicEvaluationReportSearchOptions.Locations:
                        lbxSelectedLocations.DataSource = new BindingSource(selectedOptions, null);
                        lbxSelectedLocations.DisplayMember = "Value";
                        lbxSelectedLocations.ValueMember = "Key";                        
                        break;
                    case PublicEvaluationReportSearchOptions.Venues:
                        lbxSelectedVenues.DataSource = new BindingSource(selectedOptions, null);
                        lbxSelectedVenues.DisplayMember = "Value";
                        lbxSelectedVenues.ValueMember = "Key";
                        break;
                    case PublicEvaluationReportSearchOptions.Questions:
                        lbxSelectedQuestions.DataSource = new BindingSource(selectedOptions, null);
                        lbxSelectedQuestions.DisplayMember = "Value";
                        lbxSelectedQuestions.ValueMember = "Key";
                        break;
                    case PublicEvaluationReportSearchOptions.Answers:
                        lbxSelectedAnswers.DataSource = new BindingSource(selectedOptions, null);
                        lbxSelectedAnswers.DisplayMember = "Value";
                        lbxSelectedAnswers.ValueMember = "Key";
                        break;
                }
            }
            else
            {
                //Clear the list box items
                switch (searchOption)
                {
                    case PublicEvaluationReportSearchOptions.Courses:
                        lbxSelectedCourses.DataSource = null;
                        break;
                    case PublicEvaluationReportSearchOptions.Events:
                        lbxSelectedEvents.DataSource = null;
                        break;
                    case PublicEvaluationReportSearchOptions.Locations:
                        lbxSelectedLocations.DataSource = null;
                        foreach (KeyValuePair<int, string> selItem in lbxSelectedLocations.Items)
                        {
                            MessageBox.Show(selItem.Value);
                        }
                        break;
                    case PublicEvaluationReportSearchOptions.Venues:
                        lbxSelectedVenues.DataSource = null;
                        break;
                    case PublicEvaluationReportSearchOptions.Questions:
                        lbxSelectedQuestions.DataSource = null;
                        break;
                    case PublicEvaluationReportSearchOptions.Answers:
                        lbxSelectedAnswers.DataSource = null;
                        break;
                }
            }
        }

        private void btnSearch_Click(object sender, EventArgs e)
        {
            //TODO: Get all items in the ListBoxes and pass them to the search method
            Dictionary<int, string> selCourses, selEvents, selLocations, selVenues, selQuestions, selAnswers;
            
            selCourses = new Dictionary<int, string>();
            foreach (KeyValuePair<int, string> pair in lbxSelectedCourses.Items){ selCourses.Add(pair.Key, pair.Value); }
            
            selEvents = new Dictionary<int, string>();
            foreach (KeyValuePair<int, string> pair in lbxSelectedEvents.Items) { selEvents.Add(pair.Key, pair.Value); }

            selLocations = new Dictionary<int, string>();
            foreach (KeyValuePair<int, string> pair in lbxSelectedLocations.Items) { selLocations.Add(pair.Key, pair.Value); }

            selVenues = new Dictionary<int, string>();
            foreach (KeyValuePair<int, string> pair in lbxSelectedVenues.Items) { selVenues.Add(pair.Key, pair.Value); }

            selQuestions = new Dictionary<int, string>();
            foreach (KeyValuePair<int, string> pair in lbxSelectedQuestions.Items) { selQuestions.Add(pair.Key, pair.Value); }

            selAnswers = new Dictionary<int, string>();
            foreach (KeyValuePair<int, string> pair in lbxSelectedAnswers.Items) { selAnswers.Add(pair.Key, pair.Value); }

            
        }

        private void formLinkLabel_LinkClicked(object sender, LinkLabelLinkClickedEventArgs e)
        {
            //Determine which LinkLabel raised the event
            LinkLabel sendingLabel = (LinkLabel)sender;
            Dictionary<int, string> selItems = new Dictionary<int, string>();
            Dictionary<int, string> selParItems = new Dictionary<int, string>();
            Reports.PublicCourseEvaluationReportSelection reportSearch = new PublicCourseEvaluationReportSelection();
            switch (sendingLabel.Name)
            {
                case "lkblCourses":
                    foreach (KeyValuePair<int, string> selItem in lbxSelectedCourses.Items)
                    {
                        selItems.Add(selItem.Key, selItem.Value);
                    }
                    reportSearch.LoadThisForm(this, PublicEvaluationReportSearchOptions.Courses, selItems, null);
                    break;
                case "lkblEvents":
                    //Get List of Events Selected
                    foreach (KeyValuePair<int, string> selItem in lbxSelectedEvents.Items)
                    {
                        selItems.Add(selItem.Key, selItem.Value);
                    }
                    foreach (KeyValuePair<int, string> selItem in lbxSelectedCourses.Items)
                    {
                        selParItems.Add(selItem.Key, selItem.Value);
                    }
                    //Get List Courses Selected so that we can load the list of Events based off Courses
                    reportSearch.LoadThisForm(this, PublicEvaluationReportSearchOptions.Events, selItems, selParItems);
                    break;
                case "lkblLocations":
                    foreach (KeyValuePair<int, string> selItem in lbxSelectedLocations.Items)
                    {
                        selItems.Add(selItem.Key, selItem.Value);
                    }
                    reportSearch.LoadThisForm(this, PublicEvaluationReportSearchOptions.Locations, selItems, null);
                    break;
                case "lkblVenues":
                    //Get List of Venues Selected
                    foreach (KeyValuePair<int, string> selItem in lbxSelectedVenues.Items)
                    {
                        selItems.Add(selItem.Key, selItem.Value);
                    }
                    //Get List of Locations Selected so that we can load the list of venues based off locations
                    foreach (KeyValuePair<int, string> selItem in lbxSelectedLocations.Items)
                    {
                        selParItems.Add(selItem.Key, selItem.Value);
                    }
                    reportSearch.LoadThisForm(this, PublicEvaluationReportSearchOptions.Venues, selItems, selParItems);
                    break;
                case "lkblQuestions":
                    foreach (KeyValuePair<int, string> selItem in lbxSelectedQuestions.Items)
                    {
                        selItems.Add(selItem.Key, selItem.Value);
                    }
                    reportSearch.LoadThisForm(this, PublicEvaluationReportSearchOptions.Questions, selItems, null);
                    break;
                case "lkblAnswers":
                    //Get List of Answers Selected
                    foreach (KeyValuePair<int, string> selItem in lbxSelectedAnswers.Items)
                    {
                        selItems.Add(selItem.Key, selItem.Value);
                    }
                    //Get List of Questions Selected so that we can load the list of answers based off the questions
                    foreach (KeyValuePair<int, string> selItem in lbxSelectedQuestions.Items)
                    {
                        selParItems.Add(selItem.Key, selItem.Value);
                    }
                    reportSearch.LoadThisForm(this, PublicEvaluationReportSearchOptions.Answers, selItems, selParItems);
                    break;
            }
        }
    }

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This is the 2nd form where we select the search options

public partial class PublicCourseEvaluationReportSelection : System.Windows.Forms.Form
    {
        PublicEvaluationReportSearchOptions searchOption;
        PublicCourseEvaluationReport parentForm;

        public PublicCourseEvaluationReportSelection()
        {
            InitializeComponent();
        }

        /// <summary>
        /// Methhod to load this form based on the search option and selected items
        /// </summary>
        /// <param name="parent">Parent Form</param>
        /// <param name="option">PublicEvaluationReportSearchOptions</param>
        /// <param name="selectedOptions">Selected Search Options</param>
        /// <param name="selectedParentOptions">Selected Parent Search Options</param>
        public void LoadThisForm(Form parent, PublicEvaluationReportSearchOptions option, Dictionary<int, String> selectedOptions, Dictionary<int, String> selectedParentOptions)
        {            
            //Set Form values
            parentForm = (PublicCourseEvaluationReport)parent;
            searchOption = option;
            
            lblSearch.Text = "Search Options";
            lbxOptions.DataBindings.Clear();
            Dictionary<int, string> items = new Dictionary<int, string>();
            StringBuilder strNoItems = new StringBuilder();
            switch (searchOption)
            {
                case PublicEvaluationReportSearchOptions.Courses:
                    lblSearch.Text = "Search Courses";

                    //Load list of all courses into ListBox
                    items = Course.GetEnabledCoursesList();
                    if (items.Count <= 0) { strNoItems.Append(" - No Courses found"); }
                    break;
                case PublicEvaluationReportSearchOptions.Events:
                    lblSearch.Text = "Search Events";
                    
                    //Load list of all completed Events, based on the selected courses
                    items = Event.GetCompletedEvents(DateTime.Now.AddYears(-3), DateTime.Now, selectedParentOptions);
                    if (items.Count <= 0) { strNoItems.Append(" - No Completed Events found"); }
                    break;
                case PublicEvaluationReportSearchOptions.Locations:
                    lblSearch.Text = "Search Locations";

                    //Load list of all Locations
                    items = StaffAdmin.DAL.Location.GetLocationsList(true);
                    if (items.Count <= 0) { strNoItems.Append(" - No Locations found"); }
                    break;
                case PublicEvaluationReportSearchOptions.Venues:
                    lblSearch.Text = "Search Venues";

                    //Load list of Venues based on selected Locations
                    items = Venue.GetVenueListFromLocations(selectedParentOptions);
                    if (items.Count <= 0) { strNoItems.Append(" - No Venues found"); }
                    break;
                case PublicEvaluationReportSearchOptions.Questions:
                    lblSearch.Text = "Search Evaluation Questions";

                    //Load list of all Public Course Evaluation Questions
                    items = CourseEvaluationQuestion.GetQuestionTextList(500);
                    if (items.Count <= 0) { strNoItems.Append(" - No Evaluation Questions found"); }
                    break;
                case PublicEvaluationReportSearchOptions.Answers:
                    lblSearch.Text = "Search Evaluation Answers";

                    //Load list of all Public Course Evaluation Question Answers based on selected Questions
                    items = CourseEvaluationAnswers.GetAnswerListFromMultipleQuestions(selectedParentOptions, (selectedParentOptions.Count == 0 ? true : false));
                    if (items.Count <= 0) { strNoItems.Append(" - No Evaluation Answers found"); }
                    break;
            }
            if (items.Count > 0)
            {
                //Bind list to the ListBox
                lbxOptions.DataSource = new BindingSource(items, null);
                lbxOptions.DisplayMember = "Value";
                lbxOptions.ValueMember = "Key";
                lbxOptions.SelectedItems.Clear();
                
                //Set selected items
                if (selectedOptions.Count > 0)
                {
                    int index = 0;
                    foreach (KeyValuePair<int, string> pairs in selectedOptions)
                    {
                        index = lbxOptions.Items.IndexOf(pairs);
                        if (index >= 0) { lbxOptions.SetSelected(index, true); }
                    }
                }
            }
            else{ lblSearch.Text += strNoItems.ToString(); }
            this.Show();
        }

        /// <summary>
        /// Clear selected items in the listbox
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnClearSelected_Click(object sender, EventArgs e)
        {
            lbxOptions.SelectedItems.Clear();
        }

        /// <summary>
        /// Method that returns a list of selected search items to the parent form and closes this form
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnSelect_Click(object sender, EventArgs e)
        {
            Dictionary<int, string> selItems = new Dictionary<int, string>();
            if (lbxOptions.SelectedItems.Count > 0)
            {
                foreach (KeyValuePair<int, string> selItem in lbxOptions.SelectedItems)
                {
                    selItems.Add(selItem.Key, selItem.Value);
                }
            }
            parentForm.UpdateSearchItems(searchOption, selItems);
            this.Close();
        }
    }

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Thanks Priest04,

The attached code I had already made the changes to set the listboxe's DataSource = null and I was still getting the same problem.

I won't have time today to look through your code but I'll run through it on Monday.

No, you still had it here:

public void LoadThisForm(Form parent, PublicEvaluationReportSearchOptions option, Dictionary<int, String> selectedOptions, Dictionary<int, String> selectedParentOptions)
        {            
            //Set Form values
            parentForm = (PublicCourseEvaluationReport)parent;
            searchOption = option;
           
            lblSearch.Text = "Search Options";
            lbxOptions.DataBindings.Clear();


and here

        /// <summary>
        /// Clear selected items in the listbox
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnClearSelected_Click(object sender, EventArgs e)
        {
            lbxOptions.SelectedItems.Clear();
        }

Tested it out and still was getting the same problem. So I went and looked at the selectionMode properties on each of the listboxes and changed them from None to MultiSimple and that did the trick.

Thanks for all your help guys