Question

I have a Winform application I’m modifying for a friend. It has a listview and wants me to add a checkbox to each row and make them mutually exclusive. So in my testing of how to make it work I found a strange behavior and as hopping someone could tell me what I’m missing.

If I display the List view with no checkbox checked. When I click right on the checkbox I cannot get it to check, but the row dose get selected. If I click on the item (the name in this case) in the column it does get checked and selected.

No matter where I click on a row, any checkboxes in rows not selected will be uncheck. Here is my little test program. I’m using .NET 4

public partial class Form1 : Form {
    public Form1() {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e) {
        TestListView.Items.Add("Bob");
        TestListView.Items.Add("Ann");
        TestListView.Items.Add("Frank");
    }

    void TestListView_MouseClick(object sender, System.Windows.Forms.MouseEventArgs e) {
        ListViewItem currentItem = TestListView.GetItemAt(e.X, e.Y);
        if (currentItem != null) {
            foreach (ListViewItem item in TestListView.Items) {
                if (item.Text == currentItem.Text) {
                    item.Checked = true;
                    item.Selected = !currentItem.Selected;
                }
                else 
                    item.Checked = false;
            }
        }
    }
}   

Answer 1

I’m currently having a very similar issue as well, however in response to Timwi it’s not the code doing the unchecking. I’ve been stepping through it very slowly and as the code fires when clicking on a checkbox, it states that it has checked it. But when the form resumes, it is unchecked again. After reading Timwi post, he lead me onto the answer. It’s not the code doing the unchecked, but the winforms event firing afterwards that unchecks the box. This fixes it:

My code is:

private bool allowCheck = false;
private bool preventOverflow = true;

private void lstvwRaiseLimitStore_MouseClick(object sender, MouseEventArgs e)
    {
        preventOverflow = false;
        ListViewItem item = lstvwRaiseLimitStore.HitTest(e.X, e.Y).Item;
        if (item.Checked)
        {
            allowCheck = true;
            item.Checked = false;
        }
        else
        {
            allowCheck = true;
            item.Checked = true;
        }
    }

private void lstvwRaiseLimitStore_ItemChecked(object sender, ItemCheckedEventArgs e)
    {
        if (!preventOverflow)
        {
            if (!allowCheck)
            {
                preventOverflow = true;
                e.Item.Checked = !e.Item.Checked;
            }
            else
                allowCheck = false;
        }
    }

So what it is doing, first I have to set a flag to prevent overflow, otherwise when the form is built or when you uncheck windows checking the box, it keeps looping the code and will eventually stack overflow. Next flag is the actual allow checking of the checkbox via your code and not via another method.

Clicking on them item, it locates where the click was and then sets the flag to allow a check to be done. The code then checks the box and the item checked section kicks off, becuase it was done by our code, it does nothing but reset the allowcheck flag.

If you clicked on a line, it does nothing else, however if it was a checkbox, at the end of our code, the Windows function kicks off and tries to check the box, becuase the allowcheck flag is false, the code first sets a flag to say I’m already preventing a check and then resets the check back to it’s intial status. Becuase this is done, the itemchecked event kicks off again, but the code has set the flag to prevent it from doing anything. Then the code finishes and it has prevented windows from checking the check box and only allowed our code.

Hope it helps!