Select / 根据在一个列表框中选择一个项目取消选择多个列表框中的项目 - C# Windows forms

Question

I have a scenario where I have three listboxes. Multiple Items can be selected in the listboxes. Based on the selection of items in one listbox, I need to select and deselect the corresponding rows in the other listboxes.

I have the code below, but I am missing something. When I select and deselecting the item, it selects and deselects the other rows items incorrectly.

            for (int count = 0; count < listBox_1.SelectedIndices.Count; count++)
            {
                // Determine if the item is selected.
                if (listBox_1.GetSelected(count) == true)
                {
                    listBox_2.SetSelected(listBox_1.SelectedIndices[count], false);
                    listBox_3.SetSelected(listBox_1.SelectedIndices[count], false);
                }
                else if (listBox_1.GetSelected(count) == false)
                {
                    // Select all items that are not selected.
                    listBox_2.SetSelected(listBox_1.SelectedIndices[count], true);
                    listBox_3.SetSelected(listBox_1.SelectedIndices[count], true);
                }

            }

Here Selection of items in LB1 should control the selection in LB2 and LB3. Now, since Item 2 and 3 are selected in LB1 - items 2 and 3 should be selected in LB2 and LB3 as well. But that's not what's happening.

======================================== UPDATE

How do I replicate the behavior when the user selects the items in ListBox2 or ListBox3

    private void listBox_1_SelectedIndexChanged_(object sender, EventArgs e)
    {
        listBox_2.ClearSelected();
        listBox_3.ClearSelected();

        int userSelectedIndex = listBox_1.Items.Count;
        if (listBox_1.SelectedIndices.Count > 0)
        {
            for (int count = 0; count < listBox_1.Items.Count; count++)
            {
                // Determine if the item is selected.
                if (listBox_1.GetSelected(count) == true)
                {
                    if (count <= listBox_2.Items.Count)
                        listBox_2.SetSelected(count, true);
                    if (count <= listBox_3.Items.Count)
                        listBox_3.SetSelected(count, true);
                }
                else if (listBox_1.GetSelected(count) == false)
                {
                    // Select all items that are not selected.
                    if (count <= listBox_2.Items.Count)
                        listBox_2.SetSelected(count, false);
                    if (count <= listBox_3.Items.Count)
                        listBox_3.SetSelected(count, false);
                }
            }
       }
    }

WHEN users selects items in ListBox 2, items in LB1 and LB3 should be selected as well.

    private void listBox_2_SelectedIndexChanged(object sender, EventArgs e)
    {
        listBox_1.ClearSelected();  // ITS giving error here.
        listBox_3.ClearSelected(); 
           
        int userSelectedIndex = listBox_2.Items.Count;
        if (listBox_2.SelectedIndices.Count > 0)
        {
            for (int count = 0; count < listBox_2.Items.Count; count++)
            {
                // Determine if the item is selected.
                if (listBox_2.GetSelected(count) == true)
                {
                    if (count <= listBox_1.Items.Count)
                        listBox_1.SetSelected(count, true);
                    if (count <= listBox_3.Items.Count)
                        listBox_3.SetSelected(count, true);
                }
                else if (listBox_2.GetSelected(count) == false)
                {
                    // Select all items that are not selected.
                    if (count <= listBox_1.Items.Count)
                        listBox_1.SetSelected(count, false);
                    if (count <= listBox_3.Items.Count)
                        listBox_3.SetSelected(count, false);
                }
            }
       }
    }

Answer 1

It is unclear where this code is called. I would simply clear the other list2 and list3 boxes and then set the same selected indexes as the ones in list box 1... some thing like...

listBox_2.ClearSelected();
listBox_3.ClearSelected();
foreach (int selectedItem in listBox_1.SelectedIndices) {
  listBox_2.SetSelected(selectedItem, true);
  listBox_3.SetSelected(selectedItem, true);
}

Edit per OP comment…

I am still not following what the requirements are, however, if you want all the ListBoxes to have the “same selected INDEXES” in each ListBox , then the code below may help.

One possible issue you may have with your current solution is a possible circular reference. Example, In the listBox_1_SelectedIndexChanged code, there is line of code…

listBox_2.SetSelected(count, true);

… this sets the selected index in list box 2 which will fire the listBox_2_SelectedIndexChanged event. Then… inside that event code you have the code…

listBox_1.SetSelected(count, true);

… which will fire the list box 1 event “again.”

It should be obvious that this may create an infinite circular reference where each event simply calls the other event and never ends.

Given that the code in the event needs to possibly “set” an index in one of the other ListBoxes , then it may be necessary to turn-off/unsubscribe the list box from its SelectedIndexChanged event before the code sets the index and then turn-on/re-subscribe to the event after the index has been set.

Therefore in the solution below, Since the same event is used for ALL three ListBoxes , the code turns-off/un-subscribes from each ListBox event before the code starts, and then turns-on/re-subscribes to the events when done.

In addition, as @zaggler correctly notes, checking if the ListBox actually HAS an index of the given value, it becomes necessary to check that the index is in a valid range before setting the index to avoid an index out of bounds exception.

private void listBox_SelectedIndexChanged(object sender, EventArgs e) {
  listBox_1.SelectedIndexChanged -= new EventHandler(listBox_SelectedIndexChanged);
  listBox_2.SelectedIndexChanged -= new EventHandler(listBox_SelectedIndexChanged);
  listBox_3.SelectedIndexChanged -= new EventHandler(listBox_SelectedIndexChanged);
  ListBox lb_1 = (ListBox)sender;
  ListBox lb_2;
  ListBox lb_3;
  switch (lb_1.Name) {
    case "listBox_1":
      lb_2 = listBox_2;
      lb_3 = listBox_3;
      break;
    case "listBox_2":
      lb_2 = listBox_1;
      lb_3 = listBox_3;
      break;
    default:
      lb_2 = listBox_1;
      lb_3 = listBox_2;
      break;
  }
  lb_2.ClearSelected();
  lb_3.ClearSelected();

  foreach (int selectedItem in lb_1.SelectedIndices) {
    if (selectedItem < lb_2.Items.Count) {
      lb_2.SetSelected(selectedItem, true);
    }
    if (selectedItem < lb_3.Items.Count) {
      lb_3.SetSelected(selectedItem, true);
    }
  }
  listBox_1.SelectedIndexChanged += new EventHandler(listBox_SelectedIndexChanged);
  listBox_2.SelectedIndexChanged += new EventHandler(listBox_SelectedIndexChanged);
  listBox_3.SelectedIndexChanged += new EventHandler(listBox_SelectedIndexChanged);
}

Answer 2

Here Selection of items in LB1 should control the selection in LB2 and LB3. Now, since Item 2 and 3 are selected in LB1 - items 2 and 3 should be selected in LB2 and LB3 as well. But that's not what's happening.

I would recommend looping through all items of listBox_1 ...

for (int idx = 0; idx <= listBox_1.Items.Count - 1; idx++)
            {
                if (listBox_1.GetSelected(idx))
                {
                    if (idx <= listBox_2.Items.Count)
                        listBox_2.SetSelected(idx, true);
                    if (idx <= listBox_3.Items.Count)
                        listBox_3.SetSelected(idx, true);
                }
                else
                {
                    if (idx <= listBox_2.Items.Count)
                        listBox_2.SetSelected(idx, false);
                    if (idx <= listBox_3.Items.Count)
                        listBox_3.SetSelected(idx, false);
                }
            }

Please note, I put a check as well to make sure the index would exist, otherwise it could throw an error if the index doesn't exist.