The most recent project he wanted was a little ICS generator. ICS is the iCalendar format that can be consumed by either Outlook or Google Calendar or any other calendaring utility that can accept that standard format. We needed to be able to provide some custom information and have some static information and send the ICS file into the response stream from the server so they could download the file.

I did a quick search and came across this excellent iCal class that is lightweight and did everything I needed it to do. With a couple of query string parameters being consumed on the other end I was able to have it output my custom iCal information rather quickly. If anyone is interested in the rest of the code for the iCal stuff please reply to this feed and I’ll post it.

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}
}

Unfortunately, this code failed miserably. I could not get anything but the first item in the list to be selected. So instead I decided that the selected index would have to be set as one of the last items in the Page_Load event. I then added this before the end of the postback conditional:
DeliveryDay.SelectedIndex = DateTime.Now.Day - 1;
That is when the errors started occurring. I tried to clear the selection using DeliveryDay.ClearSelection(); to give me the desired result of clearing the selected item before I set the index of the item I wanted. This also generated the same errors. I continued to try to resolve this issue by using the FindByText() and FindByValue() methods and even tried to change my list item values by adding the date to them thinking there might be something wrong with the value and the text being the same. Of course that was not the case.
Eventually I started thinking about the ListItem object. I realized that I was adding the same object to each of DropDownList's ItemCollection object. I finally realized that this was my error. So I changed my code to this:

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
for (int i = 0; i < 60; i++)
{

SetListWithMonths();
DeliveryYear.Text = DateTime.Now.Year.ToString();
DeliveryHour.SelectedIndex = 0;
DeliveryMinute.SelectedIndex = 0;
}
}

Now, each list contains their own ListItem object and there can be no sharing of the object between the different lists. I had mistakenly believed that each ListItem added to the collection would be passed by Value and that setting the Selected list item in one list would not affect the selected item in another list. After the page loads this seems to be the case but when initializing the page content using the same list item it can cause a world of grief.
I hope this post saves someone else a bunch of time because the information is invaluable to me!

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I had to learn how WPF manages the display thread. I am typically a web developer so I don’t often work in a multi-threaded environment for desktop applications. I knew I needed a thread that managed the display of each object but I didn’t know how to pump those messages back to the display object from my background thread. I decided I would research it.

I found that WPF uses something called the Dispatcher which manages the thread that is allowed to update the display. I found a couple of tutorials which walked you through creating new threads using the Dispatcher to spawn those threads. I don’t know how well it worked though because as I tried to add some fake application latency “Thread.Sleep(2000)” the whole display object would sleep for those two seconds. That is not what I wanted at all. This is the code I was using to spawn a new StartApplication Thread.

this.Dispatcher.BeginInvoke(DispatcherPriority.Normal, new StartUpApp(StartUpApplication));

Where StartUpApp was my delegate and StartUpApplication was the method that matched the delegate signature.

Anyway, that was failing miserably so I was talking to a friend of mine who’s worked with his own multi-threaded applications and we talked about threading in general. He really didn’t help me along in the process, so I took a short break from what I was working on.

I came back to reading more documentation on the MDSN and realized that the Dispatcher message pump would always push messages back to the display thread. This meant that any Thread that was started could call back to the Dispatcher and send those messages back. So, here is what I finally came up with:


private void StartAppButton_Click(object sender, RoutedEventArgs e)
{
i = 0;
Thread startUp = new System.Threading.Thread(StartUpApplication);
startUp.Start();
}

This was exactly what I was looking for. Now that I can pump messages back to the display from the processing thread I can flush out the rest of the functionality of the application.

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