WPF - How to model a loop operation in the UI - wpf

Question

I am creating a quick'n'dirty utility that will enable editing of data read sequentially from a set of files. Here's a very simplified explanation of what will happen in a single iteration of a loop:
Read a line from the input stream
Parse it and use the parsed results to populate form controls
Allow user editing and await a confirmation button click
Retrieve the updated form control values and write to the output stream
What I can't figure out is how to integrate the processing loop with the event-driven UI. For example, how do I suspend operation of the loop while waiting for user input.
I understand that this is possible by launching the loop operation on its own thread and writing code to manage its interaction with the UI thread, but I am wondering if there is a simpler approach that works out of the box.
Thanks for any ideas you may be able to offer.
Tim

Answer 1

I can think of 2 approaches to do that:
The easiest is probably to use a modal dialog: when your worker thread needs input from the user, display a dialog, which is a blocking operation. Something like that:
// Worker thread loop
while(...)
{
...
// prompt user for data (invoke synchronously on UI thread)
UserData data = (UserData)window.Invoke(PromptUserData);
...
}
...
UserData PromptUserData()
{
UserInputDialog dlg = new UserInputDialog();
dlg.ShowDialog();
return dlg.UserData;
}
The other option, if you don't want to use a modal dialog, is to use a wait handle to synchronize the worker thread and the UI:
private readonly AutoResetWaitHandle _userInputWaitHandle = new AutoResetWaitHandle(false);
...
// Worker thread loop
while(...)
{
...
// Setup the UI to allow user input
window.Invoke(SetupUIForInput);
// Wait for the input to be validated
_userInputWaitHandle.WaitOne();
...
}
...
void SetupUIForInput()
{
// Enable the UI
inputForm.Enabled = true;
// Whatever else you need to do...
...
}
void buttonOK_Click(object sender, EventArgs e)
{
// Signal the worker thread to continue
_userInputWaitHandle.Set();
}

Answer 2

You wouldn't really implement a loop in the narrow sense.
You would do something like this (pseudo code):
OnStartOperationButtonClick()
{
if(!ReadLine())
return;
ParseLineAndPopulateControls();
ShowEditingControls();
}
OnConfirmationButtonClick()
{
GetControlValuesAndWriteToOutputStream();
if(!ReadLine())
{
HideEditingControls();
return;
}
ParseLineAndPopulateControls();
}
No need for a separate thread, given that reading and parsing the line doesn't take long.