搜索项目具有自定义数据的列表框

Question

I am loading data into the list box with attached DateTime data. Now I want to search the listbox for an item that contains tagID (eg: e2003450976543). When I search the listbox I cannot find the tagID even though I can see it. I am assuming that the search parameters are not excluding the attached DateTime data. Here is my code:

class ExpiringItem
{
    private string text;
    public ExpiringItem(string text)
    {
        this.text = text;
        this.Added = DateTime.Now;
    }
    public DateTime Added { get; private set; }
    public override string ToString()
    {
        return text;
    }
}

private void timer1_Tick(object sender, EventArgs e)
{
    for (int i = listBox1.Items.Count -1; i > -1; i--)
    {
        var exp = (ExpiringItem)listBox1.Items[i];
        var timeVisible = DateTime.Now - exp.Added;
        if (timeVisible.TotalSeconds > 30)
            listBox1.Items.RemoveAt(i);

    }
}

To insert I am using: lstTagsHold.Items.Add(new ExpiringItem(txtTagID.Text));

Basically all I want to do is check if the tagID exists in the listbox or not...

For the test I am using: if (lstHold.Items.Contains(TagID))..

Answer 1

I guess the tagID is equal to this.text in your code.

You need to know that ListBox does not contain a list of string, but a list of objects. You can see the tagID because you have override the ToString() method to present the text.

And according to var exp = (ExpiringItem)listBox1.Items[i]; , the exp.text should be your tagID, but it's private . Please write a public property for it, and your tagID is there.

Answer 2

The Items.Contains methos test for identity of the param with the object stored in the ListBox.Items. But as you don't have the objects but only a string value it can't work, so you need to search through the Items..:

After making text public as JC has noted, you can access it in a function like this:

int findFirstID(ListBox lb, string id)
{
    for (int i = 0; i < lb.Items.Count; i++)
    {
        var ei = lb.Items[i] as ExpiringItem;
        // if text is public:
        if (ei.text == id) return i;
        // if it isn't:
        if (ei.ToString()== id) return i;

    }
    return -1;
}

This will return the index of the first item with the ID you search for or -1 if it is not found.

If all you want is to check if is is in the listBox you can use a little LINQ :

// if text is public:
if (listBox1.Items.Cast<ExpiringItem>().Where(x => x.text == yourID).Count() > 0) ..

// if it isn't::
if (listBox1.Items.Cast<ExpiringItem>().Where(x => x.ToString()== yourID).Count() > 0) ..