Android Question How to write a function with a return value when there is a ResumableSub call inside

beelze69 · Feb 14, 2022

Hi,

I have a User-Defined Function which returns a String type value..

Inside the function, I am invoking the SQL Query using WAIT

A broad template of the code is shown below:

Code Template:

Public Sub myfunc(pid As Long) As String
    Dim SenderFilter As Object
        dim mySqlQuery as String
        mySQLQuery="SELECT ..."

    SenderFilter=Starter.SQL.ExecQueryAsync("SQL", mySQLQuery,Null)

    Wait For (SenderFilter) SQL_QueryComplete (Success As Boolean, RS As ResultSet)
    If Success Then

        Return(RS.GetString(<Field Name>))
    Else
        Log(LastException)
    End If


End Sub

However, the IDE gives compile error saying that

'Error description: Resumable subs return type must be ResumableSub (or none)'

My Doubt:

How to write a user-defined-function returning a datatype but which is a resumable sub in it...

Thanks

agraham · Feb 14, 2022

Change the return type to ResumableSub, return the value as normal with 'Return whatever' and call it using Wait For. You can nest ResumableSubs as follows.

B4X:

Sub Button1_Click
    Wait For (test1) Complete (val As String)
    Log(val)   
End Sub

Private Sub test1 As ResumableSub
    Wait For (test2) Complete (val As String)
    Return val
End Sub

Private Sub test2 As ResumableSub
    Sleep(0)
    Return "Result"
End Sub

See this tutorial

[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

beelze69 · Feb 15, 2022

agraham said:
Change the return type to ResumableSub, return the value as normal with 'Return whatever' and call it using Wait For. You can nest ResumableSubs as follows.

B4X:

Sub Button1_Click Wait For (test1) Complete (val As String) Log(val) End Sub Private Sub test1 As ResumableSub Wait For (test2) Complete (val As String) Return val End Sub Private Sub test2 As ResumableSub Sleep(0) Return "Result" End Sub

See this tutorial

[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

Hi Agraham,

Thanks for pointing to that link!

Some more issues:

1) I get the warning 'Not all code paths return a value'

How can that be removed ?

2) I got a CursorIndexOutOfBoundsException error in SQLLITE when I did not use Do While Rs.Nextrow ... Loop ...

This is despite the fact that you know there will be only 1 record match (For example, you want the employee name given an employee id and you know there will be only one record match. You are the database designer and you have ensured primary key validation on the employee id and so you know that there will be only one unique entry for every employee_id) and there was no need to have a loop...

Is this the right way to FIRE EVERY SQLLITE query (even if the database designer knows fully well that there will be only 1 record match) ?

Please clarify..

Thanks..

agraham · Feb 15, 2022

beelze69 said:
1) I get the warning 'Not all code paths return a value'

Not from that code fragment you quoted above. If you mean your original fragment in the first post you have a Sub with a Return statement in a conditional block but not also at the end of the Sub if the conditional isn't met.

B4X:

Public Sub myfunc(pid As Long) As String
    '... some code
    If Success Then
        Return(RS.GetString(<Field Name>))
    Else
        Log(LastException)
        ' Need a Return something here'
    End If
    ' or here
End Sub

beelze69 said:
Is this the right way to FIRE EVERY SQLLITE query

Looks fine to me but I don't use SQL so I might be wrong

DonManfred · Feb 15, 2022

beelze69 said:
Inside the function, I am invoking the SQL Query using WAIT

[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

agraham · Feb 15, 2022

I already posted that link above ?

Erel · Feb 15, 2022

beelze69 said:
I got a CursorIndexOutOfBoundsException error in SQLLITE when I did not use Do While Rs.Nextrow ... Loop ...

The "do while" is not important. Calling rs.NextRow is a must.

Correct code:

B4X:

 Wait For (SenderFilter) SQL_QueryComplete (Success As Boolean, RS As ResultSet)
    If Success Then
         rs.NextRow 'must be at least one record
         Dim res As SAtring = RS.GetString(<Field Name>)
         rs.Close '<------
         Return res
    Else
        Log(LastException)
    End If
   Return "" 'or any other value that you like to represent an error

Mahares · Feb 15, 2022

Erel said:
Correct code:

Shouldn't Return rs be Return res

beelze69 · Feb 17, 2022

agraham said:
Not from that code fragment you quoted above. If you mean your original fragment in the first post you have a Sub with a Return statement in a conditional block but not also at the end of the Sub if the conditional isn't met.

B4X:

Public Sub myfunc(pid As Long) As String '... some code If Success Then Return(RS.GetString(<Field Name>)) Else Log(LastException) ' Need a Return something here' End If ' or here End Sub

Looks fine to me but I don't use SQL so I might be wrong

Thanks Agraham,

I got it ... Erel's example shows the right way to do it.. Thanks for the help...

beelze69 · Feb 17, 2022

Mahares said:
Shouldn't Return rs be Return res

Thanks Mahares

beelze69 · Feb 17, 2022

Erel said:

The "do while" is not important. Calling rs.NextRow is a must.

Correct code:

B4X:

 Wait For (SenderFilter) SQL_QueryComplete (Success As Boolean, RS As ResultSet)
    If Success Then
         rs.NextRow 'must be at least one record
         Dim res As SAtring = RS.GetString(<Field Name>)
         rs.Close '<------
         Return res
    Else
        Log(LastException)
    End If
   Return "" 'or any other value that you like to represent an error

Thanks Erel for giving this example..

beelze69 · Feb 17, 2022

DonManfred said:
[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

Thanks DonManfred

Android Question How to write a function with a return value when there is a ResumableSub call inside

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