Android Question Change DoEvents in ClsExplorer

asales · Mar 20, 2018

I'm trying to update this code of the File Explorer class:
https://www.b4x.com/android/forum/threads/class-file-explorer-with-visualization.19003/
to use Sleep(0) instead the DoEvents.

I'm stopped in this part of the code, because if I use Sleep(0) (or 100 or 1000) don't works.

B4X:

Do While WaitUntilOK
   ' Main loop - we wait until the OK btn is pressed or the back key is used
   DoEvents
Loop

I think this will be useful to @Robert Valentino too, that posted this thread (if him don't found an answer):
https://www.b4x.com/android/forum/threads/clsexplorer-without-doevents.88865/

Thanks in advance for any tips.

Claudio Oliveira · Mar 20, 2018

This code is inside private sub CommonExplorer, which is called by public subs Explorer or Explorer2. In both cases, the call to CommonExplorer is the very last statement before End Sub.
Unlike DoEvents, which interrupts processing and allows UI updating, Sleep() returns to the calling sub which, in this particular case, immediatly ends. Maybe this interrupts the code flow.
It's just a guess. I'm absolutely not sure, but even if I'm wrong, I do believe this is a good starting point and most certainly I'll learn a bit more about Sleep, Wait For and resumable subs...

Erel · Mar 20, 2018

I haven't seen the relevant code however the correct way to use sleep without changing the current code flow is by waiting for the resumable sub to complete.

B4X:

Sub BusySub As ResumableSub
 Do While WaitUntilOK
  Sleep(10)
 Loop
 Return True
End Sub

'call it like this:
Wait For (BusySub) Complete (Success As Boolean)

This is explained in the resumable subs video tutorial.

Informatix · Mar 20, 2018

asales said:
I'm trying to update this code of the File Explorer class:
https://www.b4x.com/android/forum/threads/class-file-explorer-with-visualization.19003/
to use Sleep(0) instead the DoEvents.

I'm stopped in this part of the code, because if I use Sleep(0) (or 100 or 1000) don't works.

B4X:

Do While WaitUntilOK ' Main loop - we wait until the OK btn is pressed or the back key is used DoEvents Loop

I think this will be useful to @Robert Valentino too, that posted this thread (if him don't found an answer):
https://www.b4x.com/android/forum/threads/clsexplorer-without-doevents.88865/

Thanks in advance for any tips.

Do you have any problem with DoEvents?
The code suggested by Erel seems ok but it is untested.

asales · Mar 20, 2018

Informatix said:
Do you have any problem with DoEvents?
The code suggested by Erel seems ok but it is untested.

No problem! The lib works fine.
I just want to avoid this message "DoEvents is deprecated."

Informatix · Mar 23, 2018

I tried the code suggested by Erel and it does not do what's expected because the code is not blocked. When you call the explorer, the code after this call executes immediately. A possible solution is to create a Result event and to wait for this event in the calling code but that would break all projects using the Explorer class.
Until now, I was not able to replace the DoEvents calls in my different libraries/classes/apps by a Sleep/WaitFor. Moreover I never had the slightest problem with these DoEvents so I don't understand why it is now undesirable.

Erel · Mar 25, 2018

Informatix said:
ntil now, I was not able to replace the DoEvents calls in my different libraries/classes/apps by a Sleep/WaitFor

It is difficult to reproduce the issues with DoEvents and modal dialogs. However many of the Google Play crash reports that include nativePollOnce are related to them: https://www.b4x.com/android/forum/pages/results/?query=nativePollOnce

Informatix said:
I was not able to replace the DoEvents calls in my different libraries/classes/apps by a Sleep/WaitFor

Sleep behavior is indeed different than DoEvents.
If you used DoEvents to allow the UI to be kept responsive while doing a lengthy task then you can replace it with Sleep(0), make that sub return ResumableSub and call it with Wait For (LongSub) Complete (ReturnValue As Boolean)

Informatix · Mar 26, 2018

Erel said:
It is difficult to reproduce the issues with DoEvents and modal dialogs. However many of the Google Play crash reports that include nativePollOnce are related to them: https://www.b4x.com/android/forum/pages/results/?query=nativePollOnce

https://www.b4x.com/android/forum/pages/results/?query=nativePollOnce
DoEvents is maybe complicated to use because there are cases, for example, where it cannot be used directly and must be called via CallSubDelayed (e.g. it will crash your app if you call it directly in a libGDX event, as this event is not run on the main thread). But who is to blame? The programmer or the function?

The message saying to replace DoEvents in the Log window worries many users. Alas, I have nothing to answer to them. I'm unable to replace these DoEvents by something similar.

Erel said:
Sleep behavior is indeed different than DoEvents.
If you used DoEvents to allow the UI to be kept responsive while doing a lengthy task then you can replace it with Sleep(0), make that sub return ResumableSub and call it with Wait For (LongSub) Complete (ReturnValue As Boolean)

I think that I understand how Sleep and WaitFor work (and I use both of them in my code). Nethertheless, I'm unable to replace DoEvents successfully (in ULV, in my Archiver libs, in BetterDialogs, in FileExplorer...), either because I need to block the flow where the call is made (the case discussed above) or because I need to update the UI from a progression event. For the first case, I can change the philosophy of the code and use an event to return the result of the call. This way, I can use Wait For to stop the flow and wait for the result. But in the latter case, which is the most current in my code, I do not see an alternative. Example:

B4X:

Sub PerformMainOp
   DisplayTask("Unzip toto")
   Arc.Unzip("toto")

   DisplayTask("Unzip tata")
   Arc.Unzip("tata")

   DisplayTask("Unzip tutu")
   Arc.Unzip("tutu")
End Sub

Sub DisplayTask(Text As String)
   'Displays the current task
   lblTask.Text = Text
   DoEvents 'Forces an update of the UI
End Sub

Sub UltArc_Progress(Bytes As Long)
   DisplayProgression(Bytes & "/" & TotalSize)
End Sub

Sub UpdateLabel(Lbl As Label, NewText As String)
   Lbl.Text = NewText
End Sub

Sub DisplayProgression(Text As String)
   'Displays the current progression
   CallSubDelayed3(Me, "UpdateLabel", lblProgression, Text) 'Allows to update the label from any thread
   DoEvents
End Sub

XbNnX_507 · Mar 26, 2018

if (wait for) works the way it should be then this should work...

B4X:

Sub PerformMainOp
   DisplayTask("Unzip toto")
   Arc.Unzip("toto")

   DisplayTask("Unzip tata")
   Arc.Unzip("tata")

   DisplayTask("Unzip tutu")
   Arc.Unzip("tutu")
End Sub

Sub DisplayTask(Text As String)
   'Displays the current task
   lblTask.Text = Text
   'DoEvents 'Forces an update of the UI
   wait for (RefreshUI) Complete ( Value as Object )
End Sub

Sub RefreshUI As ResumableSub
    Sleep    ( 0 )
    Return     Null
End Sub

Sub UltArc_Progress(Bytes As Long)
   DisplayProgression(Bytes & "/" & TotalSize)
End Sub

Sub UpdateLabel(Lbl As Label, NewText As String)
   Lbl.Text = NewText
End Sub

Sub DisplayProgression(Text As String)
   'Displays the current progression
   CallSubDelayed3(Me, "UpdateLabel", lblProgression, Text) 'Allows to update the label from any thread
   wait for (RefreshUI) Complete ( Value as Object )
End Sub

Informatix · Mar 26, 2018

XbNnX_507 said:

if (wait for) works the way it should be then this should work...

B4X:

Sub PerformMainOp
   DisplayTask("Unzip toto")
   Arc.Unzip("toto")

   DisplayTask("Unzip tata")
   Arc.Unzip("tata")

   DisplayTask("Unzip tutu")
   Arc.Unzip("tutu")
End Sub

Sub DisplayTask(Text As String)
   'Displays the current task
   lblTask.Text = Text
   'DoEvents 'Forces an update of the UI
   wait for (RefreshUI) Complete ( Value as Object )
End Sub

Sub RefreshUI As ResumableSub
    Sleep    ( 0 )
    Return     Null
End Sub

Sub UltArc_Progress(Bytes As Long)
   DisplayProgression(Bytes & "/" & TotalSize)
End Sub

Sub UpdateLabel(Lbl As Label, NewText As String)
   Lbl.Text = NewText
End Sub

Sub DisplayProgression(Text As String)
   'Displays the current progression
   CallSubDelayed3(Me, "UpdateLabel", lblProgression, Text) 'Allows to update the label from any thread
   DoEvents
End Sub

It's something I tried. No update at all. The label remains empty.
Note that there's a second DoEvents in DisplayProgression.

EDIT: changing the Sleep value to something else than 0 does not change anything.

XbNnX_507 · Mar 26, 2018

Informatix said:
It's something I tried. No update at all. The label remains empty.

Either we don't understand how it works or we are implementing the wrong way.
Maybe Erel could help with this.

Erel · Mar 27, 2018

I did take a quick look on this code and it is indeed not a simple change in this case. You can always add 'ignore to those lines and the warnings will disappear.

Android Question Change DoEvents in ClsExplorer

asales

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Claudio Oliveira

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Erel

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Informatix

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asales

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Informatix

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