Android Question Wait for... waits?

LucaMs · Oct 17, 2017

The Test project works: the file (sqlite DB) is saved and it is then accessible.

Real project log (shortly):
Service Create
Service Start
Wait For SubName
Activity Main Create
Activity Main Resume
** Service httputils2 Create
** Service httputils2 Start
** Service httputils2 Start
List of files received.
Downloading...
Activity Main Pause
' other "empty" Activities start
Saving file on device
Saved.
Initialize the db file:
crash -
android.database.sqlite.SQLiteCantOpenDatabaseException: unknown error (code 14): Could not open database

Wait For (SubName...) seems to not wait, correct?

Erel · Oct 17, 2017

Please create a small project that reproduces this issue and upload it. It is impossible to say what happens without seeing the code.

LucaMs · Oct 17, 2017

Erel said:
Please create a small project that reproduces this issue and upload it. It is impossible to say what happens without seeing the code.

An example without httpjobs (simulated).

Erel · Oct 17, 2017

There are several mistakes in this code:
1. If you want to wait for a sub to complete then you should make it return a ResumableSub object and use this syntax:

B4X:

Wait For (HttpJobSim1) Complete(Result As Object) 'you can change the result type

[B4X] Resumable subs that return values (ResumableSub)

2. Wait For doesn't block the program flow. Wait For is equivalent to Return where the sub will be resumed at a later point: [B4X] Resumable Subs - Sleep / Wait For
This means that Activity_Create will be executed before Service_Create is resumed and completed.

If you want that Activity_Create will wait for the resumable Service_Create to complete then you will need to change Activity_Create to:

B4X:

Sub Activity_Create(FirstTime As Boolean)
   If FirstTime Then
     Wait For Service_Complete
   End If
   Log("Starter.MyVar = " & Starter.MyVar)
End Sub

'and service create:
Sub Service_Create
   Wait For (MyRoutine) Complete (Result As Int)
   MyVar = Result
   CallSubDelayed(Main, "Service_Complete")
End Sub

I think that it is a mistake to wait for the httpjobs to complete before you load the layout. A better approach is to use CallSubDelayed to call a different sub in the activity.

LucaMs · Oct 17, 2017

Erel said:
There are several mistakes in this code:
1. If you want to wait for a sub to complete then you should make it return a ResumableSub object and use this syntax:

Watch line 17 in Starter:

Wait For (MyRoutine) Complete (Result As Int)

I have not used the same for the two "simulated" http jobs, only because it is an example .

Erel said:
2. Wait For doesn't block the program flow. Wait For is equivalent to Return where the sub will be resumed at a later point: [B4X] Resumable Subs - Sleep / Wait For
This means that Activity_Create will be executed before Service_Create is resumed and completed.

Yes, I remembered this ... afterwards
Its name is a bit misleading; it waits without waiting , the flow returns to the sub which contains the Wait For when the "waited" routine is completed.

Erel said:
If you want that Activity_Create will wait for the resumable Service_Create to complete then you will need to change Activity_Create to:

Thank you for this example.

Erel said:
I think that it is a mistake to wait for the httpjobs to complete before you load the layout. A better approach is to use CallSubDelayed to call a different sub in the activity.

As you wrote elsewhere, the Starter Service is the best place to initialize a global DB, so I tried that code (#1).

Thank you.

Erel · Oct 17, 2017

LucaMs said:
Its name is a bit misleading; it waits without waiting

Think about it like this: it is not the main thread that waits for the event (as we never want to hold the main thread) it is the resumable sub that waits for the event.

Dey · Oct 17, 2017

Erel said:
There are several mistakes in this code:
1. If you want to wait for a sub to complete then you should make it return a ResumableSub object and use this syntax:

B4X:

Wait For (HttpJobSim1) Complete(Result As Object) 'you can change the result type

[B4X] Resumable subs that return values (ResumableSub)

2. Wait For doesn't block the program flow. Wait For is equivalent to Return where the sub will be resumed at a later point: [B4X] Resumable Subs - Sleep / Wait For
This means that Activity_Create will be executed before Service_Create is resumed and completed.

If you want that Activity_Create will wait for the resumable Service_Create to complete then you will need to change Activity_Create to:

B4X:

Sub Activity_Create(FirstTime As Boolean) If FirstTime Then Wait For Service_Complete End If Log("Starter.MyVar = " & Starter.MyVar) End Sub 'and service create: Sub Service_Create Wait For (MyRoutine) Complete (Result As Int) MyVar = Result CallSubDelayed(Main, "Service_Complete") End Sub

I think that it is a mistake to wait for the httpjobs to complete before you load the layout. A better approach is to use CallSubDelayed to call a different sub in the activity.

Just to say does not center anything with the thread.

Thanks Erel is the most important feature you have entered
Wait For ResumableSub

I have rewritten all DB JRDC2 management and finally I have the situation in hand!

You just have to do a try to figure out how it works and work gets a lot easier!
Thanks again

LucaMs · Oct 17, 2017

Dey said:
is the most important feature you have entered

[OT] This one is a big revolution too:
https://www.b4x.com/android/forum/threads/b4x-xui-cross-platform-native-ui-library.84359/

Android Question Wait for... waits?

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