How to call a method from a thread?

General
1

Folks:

Thread1 is a control in Window1.
Using a pushbutton, Thread1.Start works.
Thread1.Run() works fine with a progress bar.
Now I want Tread1.Run() to call a method, Method1.
Xojo launches but then gives ThreadAccessingUIException at the call to Method1.

  1. How do I define a method that can be called from Thread1?

  2. How do I move Thread1 out of Window1 into standard Module1, so that Thread1 is independent of Window1? My intention is to launch multiple threads in a Xojo app that processes in background with no windows.

Any advice welcome :smiley:

2

There is nothing wrong is calling methods from a thread. In fact, under my Thread.Run Event is a method.

The only thing you cannot do is to update, read or write anything on the UI from a thread directly. The ThreadAccessingUIException shows your method is doing that.

If you need to get some properties from the UI, copy them into a global property and read off from there. It can be a string array, an integer, boolean or string.

One method is laid out in Updating the User Interface with the New Thread Class – Xojo Programming Blog

Before that, what we did was to use a timer. Within your method, increment a property which contains the value you want to update in the UI then use the timer to do the update.

3

Nothing in your thread is allowed to access the user interface (such as changing something in a window). You should look at the thread documentation and learn about the AddUSerInterfaceUpdate() method and the UserInterfaceUpdate event.

4

Thanks, Edwin and Tim.
Problem 1. was because Method1 output a MessageBox :frowning:
Now Method1 can be called from both the main line and the thread without error.
Yes, am using AddUSerInterfaceUpdate() method and the UserInterfaceUpdate event to update a listbox and progress bar as described in an old Forum thread. Thank you, author of that post. It seems to work fine without a timer.

5

Create a new class in your project and set its Super’s value to “Thread”. That works on Console apps too, if you really don’t need any UI.

1 Like
6

Worth remembering that the threads are cooperative and will only use a single CPU core.

7

Thanks, Arnaud. I also got this to work in code:
var t as new Thread
Addhandler t.run, AddressOf threadCode
t.Start

8

Ian, oh no!

9

If you use AddHandler remember to remove the handler before the instance is destroyed otherwise you will get a leak.

10

Just worth a note: this works specifically for threads because Xojo keeps an internal list of them. Should it be other objects, like a shell, it would vanish at the end of that method because the variable (the only reference to it) would go out of scope.