C＃在列表框上禁用Ctrl键

Question

I'm looking to disable the Ctrl key on a ListBox. I followed the example at Disable list box CTRL+C & CTRL+X in D&D . It took some playing, since I'm using System.Windows.Input and using System.Windows.Forms . I was able to resolve the references, except for the e object. It tells me there is no Handled definition within System.Windows.Forms.PreviewKeyDownEventArgs . What am I missing here? Thanks!

  private void lbSigns_PreviewKeyDown(object sender, 
                System.Windows.Forms.PreviewKeyDownEventArgs e)
    {
        //
        // This if statement detects if the Control Key is pressed.
        //
        if ((System.Windows.Input.Keyboard.Modifiers & 
          System.Windows.Input.ModifierKeys.Control) == 
                 System.Windows.Input.ModifierKeys.Control)
        {
            e.Handled = true;
        }
    }

OK, I'm getting closer with @Tsukasa 's code. Here's what I have now.

    List<int> alreadySelectedIndexes = new List<int>();

    private void lbSigns_SelectedIndexChanged(object sender, EventArgs e)
    {

        TrackSelection((ListBox)sender, alreadySelectedIndexes);

        bool allowSelection = false;

        int currentSelectedIndex = -1;

        //make sure we have an item selected
        if (!lbSigns.SelectedIndex.Equals(-1))
        {
            //if first selection we allow it
            if (alreadySelectedIndexes.Count.Equals(1))
            {
                allowSelection = true;
            }
            else
            {
                //get the last item index that was selected from our list
                currentSelectedIndex = alreadySelectedIndexes[alreadySelectedIndexes.Count - 1];

                //make sure we have a previous index item
                if ((currentSelectedIndex - 1) >= 0)
                {
                    //check if previous item before currently selected is checked
                    if (lbSigns.GetSelected(currentSelectedIndex - 1))
                    {
                        allowSelection = true;
                    }
                }

                //make sure we have a next index item
                if ((currentSelectedIndex + 1) <= lbSigns.Items.Count - 1)
                {
                    //check if next item after currently selected is checked
                    if (lbSigns.GetSelected(currentSelectedIndex + 1))
                    {
                        allowSelection = true;
                    }
                }
                //make sure we have both a next and a previous item
                if (((currentSelectedIndex - 1) >= 0) && ((currentSelectedIndex + 1) <= lbSigns.Items.Count - 1))
                {
                    //if both are selected, deny the selection
                    if (lbSigns.GetSelected(currentSelectedIndex - 1) && lbSigns.GetSelected(currentSelectedIndex + 1))
                    {
                        allowSelection = false;
                    }
                }
            }
        }

        //unselect item because it wasn't before or after an already selected item
        if (!allowSelection && !currentSelectedIndex.Equals(-1))
        {
            lbSigns.SetSelected(currentSelectedIndex, false);
        }
    }

    private void TrackSelection(ListBox listBox, List<int> alreadySelectedList)
    {
        ListBox.SelectedIndexCollection indexCollection = listBox.SelectedIndices;

        foreach (int index in indexCollection)
        {
            if (!alreadySelectedList.Contains(index))
            {
                alreadySelectedList.Add(index);
            }
        }

        foreach (int index in new List<int>(alreadySelectedList))
        {
            if (!indexCollection.Contains(index))
            {
                alreadySelectedList.Remove(index);
            }
        }
    }

But, this is letting me de-select an item surrounded by 2 selected items. Once de-selected, it won't let me re-select that item, even though it has selected items on either side of it. I added in the section that follows the comment: //make sure we have both a next and a previous item

Answer 1

Updated 2

Ok this doesn't allow deselection between selected items, although there is another issue.

Issue: you can hold down the mouse button and ctrl+mouse left and drag up and down. This doesn't call the event until finished. I'm not sure what event to hook to try and correct that.

I do however have a better way I can post later. I would create a global keyboard hook on both the left and right control keys. In the event that fires when that key is detected. If the ListBox has input focus then we handle the key causing only the shift button being able to be used to select multiple items. You want to make sure it's only when input focus is on the ListBox otherwise you would be eating the key for all other apps since it's a global hook.

        //hold already selected items. Last item will be last selected
    List<int> alreadySelectedIndexes = new List<int>();

    //used to skip listBox1_SelectedIndexChanged on TrackSelection
    bool ignoreSelectedChanged = false;

    private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        //prevent overflow of caused by TrackSelection
        if (!ignoreSelectedChanged)
        {
            TrackSelection((ListBox)sender, alreadySelectedIndexes);

            bool allowSelection = false;

            int currentSelectedIndex = -1;

            //make sure we have an item selected
            if (!listBox1.SelectedIndex.Equals(-1))
            {
                //if first selection we allow it
                if (alreadySelectedIndexes.Count.Equals(1))
                {
                    allowSelection = true;
                }
                else
                {
                    //get the last item index that was selected from our list
                    if ((alreadySelectedIndexes.Count - 1) >= 0)
                    {
                        currentSelectedIndex = alreadySelectedIndexes[alreadySelectedIndexes.Count - 1];

                        //make sure we stay in array range
                        if ((currentSelectedIndex - 1) >= 0)
                        {
                            //check if previous item before currently selected is checked
                            if (listBox1.GetSelected(currentSelectedIndex - 1))
                            {
                                allowSelection = true;
                            }
                        }

                        //make sure we stay in array range
                        if ((currentSelectedIndex + 1) <= listBox1.Items.Count - 1)
                        {
                            //check if next item after currently selected is checked
                            if (listBox1.GetSelected(currentSelectedIndex + 1))
                            {
                                allowSelection = true;
                            }
                        }
                    }
                }

                bool isSelected = false;
                if (currentSelectedIndex >= 0)
                {
                    isSelected = listBox1.GetSelected(currentSelectedIndex);

                    if (!isSelected)
                    {
                        //we can remove it from the list now
                        alreadySelectedIndexes.Remove(currentSelectedIndex);

                        //reselect it if in the middle of already selected items
                        if (alreadySelectedIndexes.Contains(currentSelectedIndex + 1) && alreadySelectedIndexes.Contains(currentSelectedIndex - 1))
                        {
                            ignoreSelectedChanged = true;
                            allowSelection = true;
                            listBox1.SetSelected(currentSelectedIndex, true);
                        }
                    }
                }
            }

            if (!currentSelectedIndex.Equals(-1) && !allowSelection)
            {
                ignoreSelectedChanged = true;
                listBox1.SetSelected(currentSelectedIndex, false);
            }

            //unselect item because it wasn't before or after the last selected item

        }
        ignoreSelectedChanged = false;
    }

    private void TrackSelection(ListBox listBox, List<int> alreadySelectedList)
    {
        ListBox.SelectedIndexCollection indexCollection = listBox.SelectedIndices;

            foreach (int index in indexCollection)
            {
                if (!alreadySelectedList.Contains(index))
                {
                    alreadySelectedList.Add(index);
                }
            }

        foreach (int index in new List<int>(alreadySelectedList))
        {
            if (!indexCollection.Contains(index))
            {
                //remove first index in list
                alreadySelectedList.Remove(index);
                //add index back to end of list so we know what was deselected
                alreadySelectedList.Add(index);
            }
        }
    }

Answer 2

            using System;
            using System.Collections.Generic;
            using System.ComponentModel;
            using System.Data;
            using System.Drawing;
            using System.Linq;
            using System.Text;
            using System.Threading.Tasks;
            using System.Windows.Forms;

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

                    private void listBox1_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e)
                    {
                        if (e.Control)
                        {
                            return;
                        }
                    }
                }
            }