从日历事件中设置usercontrol属性

Question

On the following code the method that's calling the property change is SetCaloriesBurnedStats(selectedDate) , everything else is working correctly.

I have a simple user control:

public string BigText { get; set; }
public string SmallText { get; set; }
public Color BigTextColor{get; set;}
public bool ArrowUp{get; set;}
public string SubBigText{get; set;}

protected void Page_Load(object sender, EventArgs e)
{
    lblBigText.Text = BigText;
    lblSmallText.Text = SmallText;
    lblBigText.ForeColor = BigTextColor;
    lblSubBigText.ForeColor = BigTextColor;
    lblSubBigText.Text = SubBigText;

    if (ArrowUp)
    {
        imgArrow.ImageUrl = "~/Images/trend-up-arrow.jpg";
    }
    else
    {
        imgArrow.ImageUrl = "~/Images/trend-down-arrow.jpg";
    }
}

It works fine on page load on my web forms, but I'm trying to set it from a calendar selectionchange event.

protected void Calendar_SelectionChanged(object sender, EventArgs e)
{
    DateTime selectedDate = Calendar.SelectedDate.Date;
    DateTime today = DateTime.Now.Date;

    if (selectedDate == today)
    {
        lblLogDayHeader.Text = "Today's Activity Log";
        lblSmallDate.Text = "Today";
    }
    else
    {
        lblLogDayHeader.Text = String.Concat("Activity Log For: ", Calendar.SelectedDate.ToShortDateString());
        lblSmallDate.Text = Calendar.SelectedDate.ToShortDateString();
    }

    SetActivityTable(selectedDate);
    SetCaloriesBurnedStats(selectedDate);
}

private void SetCaloriesBurnedStats(DateTime selectedDate)
{
    if (selectedDate.Date == DateTime.MinValue) { return; }

    using (var db = new DbConn())
    {
        var todaysCaloriesBurned =
            db.Activity.Where(c => c.Id == pId && SqlFunctions.DateDiff("DAY", c.DateOfEntry, selectedDate) == 0).Select(c => c.Calories).DefaultIfEmpty(0).Sum();

        Stat_CaloriesBurnedToday.BigText = todaysCaloriesBurned.ToString();
    }
}

On my webform I have the control added.

<uc1:Stat runat="server" BigTextColor="#07beb8" SubBigText="cals" SmallText="Calories burned today" ID="Stat_CaloriesBurnedToday" />

It always returns NULL, but in the debugger I'm watching the BigText property being set to the correct value, but when I continue running the app it shows nothing on the label.

This only happens when I'm trying to set the BigText property from the Calendar selectionchange event.

Here is the code for my web forms page load which doesn't call the event if the calendar date isn't changed.

protected void Page_Load(object sender, EventArgs e)
{
    DateTime calSelDate = Calendar.SelectedDate;
    DateTime selectedDate = DateTime.Now.Date;
    if (!Page.IsPostBack)
    {
        if (calSelDate == DateTime.MinValue)
        {
            SetActivityTable(selectedDate);
            SetCaloriesBurnedStats(selectedDate);
        } //Else set the table and stats in the Calender_SelectedDate event
    }
    ActivityChart = ReturnAllActivitiesForChart();
    SetAvgCaloriesBurnedDailyStats();
}

What am I missing here?

Answer 1

What am I missing here?

You are missing the most important part of the puzzle...the Page Life Cycle. Here's what's happening

1. The page loads -> BigText hasn't been set. It's null
2. The user control loads -> lblBigText is assigned the value of BigText which is null
3. You click on the Calendar and the page posts back
4. The page loads again -> BigText hasn't been set. It's null
5. The user control again -> lblBigText is assigned the value of BigText which is null
6. Calendar_SelectionChanged event is triggered -> BigText is set
7. The page is sent back to the user

Notice in step 6 that Calendar_SelectionChanged is triggered after Page_Load and the BigText property is actually set. However, label lblBigText is not assigned the value of this property

Solution

Open move all the initialization logic inside your UserControl's Page_Load "event" to an event that is triggered later in the page life cycle and before Render is triggered. The safest place would be OnPreRender as shown below...

    public string BigText { get; set; }
    public string SmallText { get; set; }
    public Color BigTextColor{get; set;}
    public bool ArrowUp{get; set;}
    public string SubBigText{get; set;}

    protected override void OnPreRender(object sender, EventArgs e)
    {
        base.OnPreRender(e);

        lblBigText.Text = BigText;
        lblSmallText.Text = SmallText;
        lblBigText.ForeColor = BigTextColor;
        lblSubBigText.ForeColor = BigTextColor;
        lblSubBigText.Text = SubBigText;

        if (ArrowUp)
        {
            imgArrow.ImageUrl = "~/Images/trend-up-arrow.jpg";
        }
        else
        {
            imgArrow.ImageUrl = "~/Images/trend-down-arrow.jpg";
        }
    }

Always remember that event handlers are always triggered after OnLoad and Page_Load but before OnPreRender .