Winforms checkedlistbox检查一个项目

Question

I have a CheckedListBox control on my form, and I want the user to only be able to check one item at a time within this list (so effectively I'd want something that would mimic a "RadioListBox").

Is this possible to do with a CheckedListBox or would I have to improvise doing it some other way?

The CheckedListBox is populated on the form load by loading items from a database, in case that matters.

Thanks

Edit

I think I should clarify, I am not looking to limit the amount a user can SELECT (ie the SelectionMode property), rather how many they can CHECK.

Answer 1

You could do it by adding an event check on CheckedListBox for ItemCheck and use function like this:

    private static bool checkIfAllowed(CheckedListBox listBox) {
        if (listBox.CheckedItems.Count > 0) {
            return false;
        }
        return true;
    }

Then in the event you would have like:

  if (checkIfAllowed) { 
     ...
  } else {

  }

Additionally you could improve this by adding another function/method that will uncheck all items before allowing item to be checked. So when users click some checkbox all other checkboxes are unchecked.

To uncheck all checked items just use:

    private static void uncheckAll(CheckedListBox listBox) {
        IEnumerator myEnumerator;
        myEnumerator = listBox.CheckedIndices.GetEnumerator();
        int y;
        while (myEnumerator.MoveNext() != false) {
            y = (int)myEnumerator.Current;
            listBox.SetItemChecked(y, false);
        }
    }

So in ItemCheck event you would have to run uncheckAll(yourListBox) first and then simply let the item be checked.

Edit: I've tested it with following code and it works. Without the if it throws exception.

    private void checkedListBox1_ItemCheck(object sender, ItemCheckEventArgs e) {
        if (e.NewValue == CheckState.Checked) {
            IEnumerator myEnumerator;
            myEnumerator = checkedListBox1.CheckedIndices.GetEnumerator();
            int y;
            while (myEnumerator.MoveNext() != false) {
                y = (int)myEnumerator.Current;
                checkedListBox1.SetItemChecked(y, false);
            }
        }

    }

Answer 2

尝试设置.SelectionMode = SelectionMode.One属性。

Answer 3

This code is could be much more simple, requires one variable. Every time you will check a new box, it will uncheck the last one, leading to the fact that there won't be two checked items or more checked at the time. Make sure the property SelectionMode = SelectionMode.One; is set as mentioned.

    private int lastCheck = -1;
    private void CheckListBox_IndexChanged(object sender, EventArgs e) {
        int toUncheck = lastCheck;
        if (toUncheck != -1)
            CheckListBox.SetItemChecked(toUncheck, false);
        lastCheck = CheckListBox.SelectedIndex;
        CheckListBox.SetItemChecked(lastCheck, true);
    }

Or alternativly you could set lastCheck to the default checked box if required, do this by:

    private void FormFoo_Load(object sender, EventArgs e) {
        CheckListBox.SelectedIndex = 0;
        lastCheck = CheckListBox.SelectedIndex;
    }

and then the rest of the code that I mentioned above comes below.

Notice*: I've used lastCheck = **CheckListBox.SelectedIndex;** to support keyboard moving, just in case.

Answer 4

I had to do something similar to select a single user from a massive list. There isn't a RadioListBox to speak of, so I just coded it manually...

Sorry it's in VB, I just pasted it in, the logic is the same.

Private m_NoFire As Boolean = False

Private Sub lstSource_ItemCheck( _
        ByVal sender As Object, _
        ByVal e As System.Windows.Forms.ItemCheckEventArgs) Handles lstSource.ItemCheck

    'When the checked state is set programatically,
    'this event will still fire and cause the loop
    'to run - infinatly. This line prevents that.
    If m_NoFire Then Exit Sub
    m_NoFire = True

    'Ensure only one item is selected
    For i As Integer = 0 To lstSource.Items.Count - 1
        If Not lstSource.SelectedIndex = i Then
            lstSource.SetItemChecked(i, False)
        End If
    Next

    m_NoFire = False

End Sub '-- lstSource_ItemCheck