在Winform应用程序中如果列表框为空或项目小于0时如何停止计时器

Question

I am making a windows app.

• A button1 which gets the items in listBox1 from server at the start.
• A button2 which starts the timer1.
• A timer1 which removes items from listBox1 .
• A progressBar1 which shows the progress of this process.

Here is the code:

private void button1_Click(object sender, EventArgs e)
{
    jabber.Send("<iq type='get' to='" + textBox1.Text + "@conference.jabber.com' id='qip_1026'><query xmlns='http://jabber.org/protocol/muc#admin'><item affiliation='outcast' /></query></iq>");
}

private void button2_Click(object sender, EventArgs e)
{
    progressBar1.Maximum = listBox1.Items.Count;
    timer1.Start();
    timer1.Interval = 4000;
}

private void timer1_Tick(object sender, EventArgs e)
{
    if (listBox1.Items.Count > 0)
    {
        jabber.Send("<iq type='set' to='" + textBox7.Text + "@conference.jabber.com'><query xmlns='http://jabber.org/protocol/muc#admin'><item jid='" + listBox1.Items[0].ToString() + "' affiliation='none'/></query></iq>");
        listBox1.Items.RemoveAt(0);
        progressBar1.Value += 1;
        label.Text = listBox1.Items.Count.ToString();
    }
    else
    {
        timer1.Enabled = False;
    }
}

The above code works well till there is one item left in listBox1.

The error is:

System.ArgumentOutOfRangeException was unhandled Message=InvalidArgument=Value of '0' is not valid for 'index'. Parameter name: index

It raises an error when listBox1 reaches 0. I want to stop the timer when listbox1 is empty or gets no items or 0 items.

Answer 1

try this

            int count = City.Items.Count - 1;
            for (int i = count; i > 0; i--){
                City.Items.RemoveAt(i);
               }

Answer 2

Here is what worked for me.

private void button1_Click(object sender, EventArgs e)
{
jabber.Send("<iq type="get" to="" + textBox1.Text + "@conference.jabber.com" id="qip_1026"><query xmlns="http://jabber.org/protocol/muc#admin"><item affiliation="outcast" /></query></iq>");
}

private void button2_Click(object sender, EventArgs e)
{
progressBar1.Maximum = listBox1.Items.Count;
progressBar1.Value = 0;
// Set the timer interval to four seconds
timer1.Interval = 4000;
// Start the timer
timer1.Start();
}

private void timer1_Tick(object sender, EventArgs e)
 {
// Disable the timer while we are working in this procedure so
// it doesn't tick while we are working in this procedure
timer1.Enabled = False;
// Send only if there are items in the ListBox
if (listBox1.Items.Count > 0)
{
    jabber.Send("<iq type="set" to="" + textBox7.Text + "@conference.jabber.com"><query xmlns="http://jabber.org/protocol/muc#admin"><item jid="" + listBox1.Items[0].ToString() + "" affiliation="none" /></query></iq>");
    listBox1.Items.RemoveAt(0);
    progressBar1.Value += 1;
    label.Text = listBox1.Items.Count.ToString();
}
// Re-enable only if there are items left in the ListBox
if (listBox1.Items.Count > 0)
{
     timer1.Enabled = True;
}
 }

Answer 3

The problem is in this code:

  private void timer1_Tick(object sender, EventArgs e)
    {
        if (listBox1.Items.Count > 0)
        {
            jabber.Send("<iq type='set' to='" + textBox7.Text + "@conference.jabber.com'><query xmlns='http://jabber.org/protocol/muc#admin'><item jid='" + listBox1.Items[0].ToString() + "' affiliation='none'/></query></iq>");
            listBox1.Items.RemoveAt(0);
            progressBar1.Value += 1;
            label.Text = listBox1.Items.Count.ToString();
        }
        else
        {
            timer1.Enabled = False;
        }
    }

So what is happening is that you are using count to check >0 then calling jabber to do the work, It the call becomes slow- you will see multiple timers getting fired back. So a big queue will be collected there. You need to modify the code a bit here using lock to hold the list and allow jabber to do its work:

private void timer1_Tick(object sender, EventArgs e)
    {
        lock (listBox1)
        {
            if (listBox1.Items.Count > 0)
            {
                jabber.Send("<iq type='set' to='" + textBox7.Text +
                            "@conference.jabber.com'><query xmlns='http://jabber.org/protocol/muc#admin'><item jid='" +
                            listBox1.Items[0].ToString() + "' affiliation='none'/></query></iq>");
                listBox1.Items.RemoveAt(0);
                progressBar1.Value += 1;
                label.Text = listBox1.Items.Count.ToString();
            }
            else
            {
                timer1.Enabled = False;
            }
        }
    }

Lock will also ensure that the items are removed correctly. To save the file as per comment below :

 public class ChatHistoryManager
{
    private readonly RichTextBox richTextBox;
    private Timer timer = new Timer();
    public ChatHistoryManager(RichTextBox richTextBox)
    {
        this.richTextBox = richTextBox;
        this.InitializeTimer();
    }

    public string Location { get; set; }
    private void InitializeTimer()
    {
        this.timer.Tick += timer_Tick;
        this.timer.Enabled = true;          
        this.timer.Interval = (int) TimeSpan.FromHours(1).TotalMilliseconds;
    }

    void timer_Tick(object sender, EventArgs e)
    {
        this.SaveFile();
    }

    public void SaveFile()
    {
        //Save the file to the location
        this.richTextBox.SaveFile(this.Location,RichTextBoxStreamType.RichText);
    }

    public void Stop()
    {
        this.timer.Stop();
    }
}

Now we need to set in form like this:

  private void Form1_Load(object sender, EventArgs e)
    {
        ChatHistoryManager chatHistoryManager = new ChatHistoryManager(this.richTextBox1);
        chatHistoryManager.Location = @"C:\Development\test.txt";
    }