ASP.NET C＃AJAX控件倒数计时器仅在对未来时间进行硬编码时才有效

Question

I have a AJAX C# ASP.NET control and it works properly (counts down from 2 hours from current time only when the datetime is hardcoded. I would like to pass in dates as a variable but every time I do so, the timer stops working.

Here's what works...

 protected void Timer1_Tick(object sender, EventArgs e)
    {
        String DateTimeFuture = DateTime.Now.AddHours(2).ToString();
        DateTime NeededByDateTime = DateTime.Parse("03/18/2017 10:00:00 AM");
        TimeSpan time1 = new TimeSpan();
        time1 = NeededByDateTime - DateTime.Now;
        if ((time1.Hours == 0) && (time1.Minutes == 0) && (time1.Seconds == 0))
        {
            Label1.Text = "Time Expired!";
            //Return article to results
        }
        else
        {
            string countDown = string.Format("{0} Days, {1} Hours, {2} Minutes, {3} Seconds til launch.", time1.Days, time1.Hours, time1.Minutes, time1.Seconds);
            Label1.Text = countDown.ToString();
        }

    }

Here's what doesn't work...

protected void Timer1_Tick(object sender, EventArgs e)
    {
        String DateTimeFuture = DateTime.Now.AddHours(2).ToString();
        DateTime NeededByDateTime = DateTime.Parse(DateTimeFuture);
        TimeSpan time1 = new TimeSpan();
        time1 = NeededByDateTime - DateTime.Now;
        if ((time1.Hours == 0) && (time1.Minutes == 0) && (time1.Seconds == 0))
        {
            Label1.Text = "Time Expired!";
        }
        else
        {
            string countDown = string.Format("{0} Days, {1} Hours, {2} Minutes, {3} Seconds til launch.", time1.Days, time1.Hours, time1.Minutes, time1.Seconds);
            Label1.Text = countDown.ToString();
        }

    }

Any ideas as to why it isn't working for the second piece of code?

UPDATE:

If you would like to try to get the example working for your environment, you'll need the following code in your page.

 <form method="post" runat="server" action="Page.aspx">
                <asp:ScriptManager ID="ScriptManager1" runat="server" />

            <asp:UpdatePanel ID="UpdatePanel1" Visible="true" runat="server" >
                <ContentTemplate>
                    <asp:Timer ID="Timer1" runat="server" Interval="1000" OnTick="Timer1_Tick">
                    </asp:Timer>
                    <asp:Label ID="Label1" runat="server"></asp:Label>
                </ContentTemplate>
            </asp:UpdatePanel>
</form>

Answer 1

What exactly doesn't work? Does it throw an exception. What is the value of the contentNeededByDateTime variable after you parse the date? Is it correct?

There may be an issue with the current culture. So to make sure that you pass the correct format to the parser, instead of ToString(), use some explicit formatting: http://www.csharp-examples.net/string-format-datetime/

I assume this is just a test code and you're going to pass the variable as a string parameter. So you just need to make sure that you pass the value in the correct format.

UPDATE

Based on the comments bellow, I understand the issue a little bit more. You can't declare the date inside the method because it gets updated every time this method is called which is probably every second. If you want to be able to have a countdown for each user. Get the date and time when a user request the page with the timer and save it to Session:

Session["NeededByDateTime"] = DateTime.Now.AddHours(2);

And then the method would look like this:

protected void Timer1_Tick(object sender, EventArgs e)
{
    //for the sake of simplicity but you should check if it exists first
    DateTime NeededByDateTime = (DateTime)Session["NeededByDateTime"]; 

    time1 = NeededByDateTime - DateTime.Now;
    if ((time1.Hours == 0) && (time1.Minutes == 0) && (time1.Seconds == 0))
    {
        Label1.Text = "Time Expired!";
    }
    else
    {
        string countDown = string.Format("{0} Days, {1} Hours, {2} Minutes, {3} Seconds til launch.", time1.Days, time1.Hours, time1.Minutes, time1.Seconds);
        Label1.Text = countDown.ToString();
    }

}

Answer 2

Your example won't work, since time1 is always going to be equal to 2 hours every time the Timer calls the Tick method.

protected void Timer1_Tick(object sender, EventArgs e)
{
    String DateTimeFuture = DateTime.Now.AddHours(2).ToString(); // NOW + 2 HOURS
    DateTime NeededByDateTime = DateTime.Parse(DateTimeFuture);
    TimeSpan time1 = new TimeSpan();
    time1 = NeededByDateTime - DateTime.Now; // NOW + 2 HOURS - NOW = 2 HOURS
    if ((time1.Hours == 0) && (time1.Minutes == 0) && (time1.Seconds == 0))
    {
        Label1.Text = "Time Expired!";
    }
    else
    {
        string countDown = string.Format("{0} Days, {1} Hours, {2} Minutes, {3} Seconds til launch.", time1.Days, time1.Hours, time1.Minutes, time1.Seconds);
        Label1.Text = countDown.ToString();
    }
}

You should declare the NeededByDateTime variable outside the Tick method, so it remains constant and not updated on every tick.

private DateTime NeededByDateTime = DateTime.Now.AddHours(2); //.., or whatever you want 

protected void Timer1_Tick(object sender, EventArgs e)
{
    TimeSpan time1 = NeededByDateTime - DateTime.Now;
    if ((time1.Hours == 0) && (time1.Minutes == 0) && (time1.Seconds == 0))
    {
        Label1.Text = "Time Expired!";
    }
    else
    {
        string countDown = string.Format("{0} Days, {1} Hours, {2} Minutes, {3} Seconds til launch.", time1.Days, time1.Hours, time1.Minutes, time1.Seconds);
        Label1.Text = countDown.ToString();
    }
}