Threads Not Returning Key:Value Pairs

I am writing a small app (using 2022r4.1) that will run on a Windows tablet connected to a (sometimes there) WiFi network. As such, I must have a local copy of some MSSQL data, which I have chosen to store locally using SQLite.

Normally, the data will be synchronized every minute when on WiFi and be perhaps a dozen records. Total time about 3-4 seconds. But if the device is new or has been offline for while there might be 1000 records or so, and the app hangs while bringing them in.

Enter a thread. The last time I used them it was a beautiful disaster. The threads worked beautifully, and the ODBC driver (written in the 1990s) was a disaster; it did not like multiple threads calling it. This time things are more modern.

When the updates are occurring I want to show the user a small progress bar that something is happening in the background. For this I need to use the method AddUserInterfaceUpdate and the event UserInterfaceUpdate. I prefer to do the synchronization at the App level, not specifically tied to a window, and therefore I added a Thread property a couple of handlers for the Run and UserInterfaceUpdate of this property. This is the same technique that I use to handle timers when writing services for Windows, and it works like a charm.

Here is the setup code:

thdSyncPacking = new Thread
AddHandler thdSyncPacking.UserInterfaceUpdate, AddressOf UpdateProgressBars
AddHandler thdSyncPacking.Run, AddressOf SyncRemotePacking
thdSyncPacking.Priority = 1

I start the thread with thdSyncPacking.Run and SyncRemotePacking computes the progress and does this after each record is processed:


When the event fires I get a set of key:value pairs. And they are all empty.

Thinking my declaration was incorrect I added the thread to one of my windows and handled the events normally. I again got empty pairs.

Could someone please enlighten me as to why this might be happening? I don’t HAVE to have the progress bar, but it sure would be nice.

What is the method signature of UpdateProgressBars?

When the event fires, you should be getting an array of dictionaries.

Please make a sample project and post it so we can see what you are doing.

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Sorry Julia and Greg; my client has had me working on other things. I will try to get a sample app uploaded today.

Greg: I am getting the array. It’s just empty.

Thanks to both of you, but I found my problem in setting up a simple test program. I was not going deep enough into my array of dictionaries and was misreading what the debugger was telling me. Hair sufficiently pulled out, I will proceed with my original project.

However, I will show the three basic elements for anyone that might find them useful later. First the thread setup in App.Opening:

' This code appears in App.Opening
' thdTestSync is a Thread property defined in App

' Set up the thread to do something and handle updates from that something
thdTestSync = new Thread
AddHandler thdTestSync.UserInterfaceUpdate, AddressOf UpdateDisplay
AddHandler thdTestSync.Run, AddressOf TestSync
thdTestSync.Priority = 1

' Start the thread

Next, the updating of progress in TestSync:

' This is TestSync(t As Thread).  It just updates the progress

var lngRows As Int64

for lngRows = 1 to 10
  ' Keep track of progress


Finally, the displaying of progress triggered by UserInterfaceUpdate:

' This is Update Display(t As Thread, dcData() As Dictionary).  It shows the progress.

' dcData is an array of dictionaries.  Must step through the array
for each dcEntry as Dictionary in dcData
  ' dcEntry is one of the dictionaries in the array.  Must also step through the the dictionary, though each has only one entry
  for each deList As DictionaryEntry in dcEntry
    ' deList is the sole Dictionary Entry in dcEntry.  Show its key:value pair
    wndMain.lstResults.AddRow deList.Key.StringValue + " = " + deList.Value.StringValue


I think the boils the Thread handling concept down to its bare minimum.

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