Android Question Sleep(0) and Msgbox2Async is crashing

divinglog · Aug 27, 2020

Hello

When I use Sleep together with async messagebox (in a class module) the code is crashing. Removing Sleep(0) from the loop works and the messagebox is shown, but the progressdialog is not shown. Is there any way to use both together?

B4X:

Public Sub Import(ImportFile As String) As ResumableSub
    ProgressDialogShow2("Importing...", False)
 
    For j = 0 To ImportTable.RowCount - 1
        'Prepare source data code
        Sleep(0)
    Next
 
    ProgressDialogHide
    Msgbox2Async("Do you want to import %1 rows?", "Import", "Yes", "", "No", Null, True) '< Crash when using Sleep(0) in the loop
    Wait For Msgbox_Result (MsgResult As Int)
 
    If MsgResult = DialogResponse.POSITIVE Then
        '...
    End If
End Sub

Crash Log:

B4X:

java.lang.RuntimeException: java.lang.NullPointerException: Attempt to read from field 'java.lang.ref.WeakReference anywheresoftware.b4a.BA$SharedProcessBA.activityBA' on a null object reference
    at anywheresoftware.b4a.keywords.Common$13.run(Common.java:1706)
    at android.os.Handler.handleCallback(Handler.java:883)
    at android.os.Handler.dispatchMessage(Handler.java:100)
    at android.os.Looper.loop(Looper.java:214)
    at android.app.ActivityThread.main(ActivityThread.java:7356)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
Caused by: java.lang.NullPointerException: Attempt to read from field 'java.lang.ref.WeakReference anywheresoftware.b4a.BA$SharedProcessBA.activityBA' on a null object reference
    at anywheresoftware.b4a.keywords.Common.Msgbox2Async(Common.java:486)
    at com.divinglog.divelog.import$ResumableSub_Import.resume(import.java:361)
    at anywheresoftware.b4a.keywords.Common$13.run(Common.java:1704)
    ... 7 more

DonManfred · Aug 28, 2020

The sub return as soon as you use sleep or wait for.
make the datafilling a resumeablesub.

[B4X] Resumable Subs - Sleep / Wait For

New video tutorial: Resumable subs is a new feature added in B4J v5.50 / B4i v4.00 / B4A v7.00. It dramatically simplifies the handling of asynchronous tasks. (This feature is a variant of stackless coroutines.) The special feature of resumable subs is that they can be paused, without...

www.b4x.com

[B4X] Resumable subs that return values (ResumableSub)

Remember that that a call to Sleep or Wait For in a resumable sub causes the code flow to return to the parent. Example: Sub Button1_Click Sum(1, 2) Log("after sum") End Sub Sub Sum(a As Int, b As Int) Sleep(100) 'this will cause the code flow to return to the parent Log(a + b) End Sub...

www.b4x.com

Erel · Aug 28, 2020

I'm not sure where this error comes from. Can you reproduce it in a small project and upload it?

divinglog · Aug 28, 2020

Erel said:
I'm not sure where this error comes from. Can you reproduce it in a small project and upload it?

No problem, I've attached a small project. Thank you Erel!

Edit: OK, I found out that the code is working directly in the Activity module. If it is in a class module, it crashes. So I think the activity reference is lost because of the Sleep() function and the messagebox cannot be displayed.

agraham · Aug 28, 2020

divinglog said:
I found out that the code is working directly in the Activity module. If it is in a class module, it crashes

I confirm this. It looks like it is something arcane to do with the code being in a class.

Erel · Aug 30, 2020

It is related to the class not having an activity context.

It will work with this code:

B4X:

Sub Class_Globals
    Private stub As Button 'ignore
End Sub

divinglog · Aug 30, 2020

Perfect, thank you Erel, that works!

JohnC · Aug 31, 2020

Erel said:
It is related to the class not having an activity context.

It will work with this code:

B4X:

Sub Class_Globals Private stub As Button 'ignore End Sub

Will a permanent fix for this be in the next version of B4A so this line doesn't need to be added?

Erel · Aug 31, 2020

It might change at some point. I cannot say for now.

JohnC · Aug 31, 2020

Is this an issue that is related to this bug?

Wait For with CallSub doesn't work

Hi, I want to do some Jobs on start of an App. Since there are user interactions and I have to handle with MsgBoxAsync and Wait For, there are Services to start and so on, it's quite difficult to keep the order of the jobs. Especially because anything runs in Activity_Create, and some jobs...

www.b4x.com

Erel · Sep 1, 2020

Yes and the same solution works. It will be fixed but not in 10.2.

Android Question Sleep(0) and Msgbox2Async is crashing

divinglog

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