Check List Box before Adding New Item

问题

I am trying to check that an item doesn't already exist in a list box before I add the new item.

            if (TeamNameTextBox.Text != "")
        {
            if (TeamNameListBox.Items.FindByValue(TeamNameListBox.Text) == null)
            {
                TeamNameListBox.Items.Add(TeamNameTextBox.Text);
                TeamNameTextBox.Text = "";

                int teamCountUpdate = TeamNameListBox.Items.Count;
                if (teamCountUpdate == 1)
                {
                    TeamCount.Text = teamCountUpdate.ToString() + " Team";
                }
                else
                {
                    TeamCount.Text = teamCountUpdate.ToString() + " Teams";
                }
            }
            else
            {
                AddTeamSeasonError.Text = "This team has already been added";
            }
        }
        else
        {
            AddTeamSeasonError.Text = "Please select a team";
        }

I have got it to check if the text box is blank, but I need to check that the item a user is trying to add is not already in the the list box.

I have tried the line:

if (TeamNameListBox.Items.FindByValue(TeamNameListBox.Text) == null)

But that doesn't work, any suggestions on how I can do the check?

回答1:

think you should at least try to use TeamNameTextBox instead of TeamNameListBox as argument

if (TeamNameListBox.Items.FindByValue(TeamNameTextBox.Text) == null)

回答2:

Use this:

if (!TeamNameListBox.Items.Contains(TeamNameTextBox.Text))
                TeamNameListBox.Items.Add(TeamNameTextBox.Text);

回答3:

I suppose you mean

// search if the textbox value is found in the list. this comment shouldn't be part of the code
if (TeamNameListBox.Items.FindByValue(TeamNameTextBox.Text) == null)

instead of

if (TeamNameListBox.Items.FindByValue(TeamNameListBox.Text) == null) // code from question

EDIT: There is no need to put the name of the type of the control next to the variable.
i.e. instead of TeamNameListBox, use teamNames. And, instead of TeamNameTextBox, use teamName.

来源：https://stackoverflow.com/questions/15532657/check-list-box-before-adding-new-item

标签

ASP.NET

listbox