Remember that that a call to Sleep or Wait For in a resumable sub causes the code flow to return to the parent.
Example:
Output:
This is the reason why it is not possible to simply return a value.
Solution
Resumable subs can return a new type named ResumableSub. Other subs can use this value to wait for the sub to complete and get the desired return value.
Output:
The above Button1_Click code is equivalent to:
The steps required are:
1. Add As ResumableSub to the resumable sub signature.
2. Call Return with the value you like to return.
3. In the calling sub, call the resumable sub with Wait For (<sub here>) Complete (Result As <matching type>)
Notes & Tips
- If you don't need to return a value but still want to wait for the resumable sub to complete then return Null from the resumable sub and set the type in the calling sub to Object.
- Multiple subs can safely call the resumable sub. The complete event will reach the correct parent.
- You can wait for resumable subs in other modules (in B4A it is relevant for classes only).
- The Result parameter name can be changed.
Example:
B4X:
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 Subafter sum
3
This is the reason why it is not possible to simply return a value.
Solution
Resumable subs can return a new type named ResumableSub. Other subs can use this value to wait for the sub to complete and get the desired return value.
B4X:
Sub Button1_Click
Wait For(Sum(1, 2)) Complete (Result As Int)
Log("result: " & Result)
Log("after sum")
End Sub
Sub Sum(a As Int, b As Int) As ResumableSub
Sleep(100)
Log(a + b)
Return a + b
End SubOutput:
3
result: 3
after sum
The above Button1_Click code is equivalent to:
B4X:
Sub Button1_Click
Dim rs As ResumableSub = Sum(1, 2)
Wait For(rs) Complete (Result As Int)
Log("result: " & Result)
Log("after sum")
End SubThe steps required are:
1. Add As ResumableSub to the resumable sub signature.
2. Call Return with the value you like to return.
3. In the calling sub, call the resumable sub with Wait For (<sub here>) Complete (Result As <matching type>)
Notes & Tips
- If you don't need to return a value but still want to wait for the resumable sub to complete then return Null from the resumable sub and set the type in the calling sub to Object.
- Multiple subs can safely call the resumable sub. The complete event will reach the correct parent.
- You can wait for resumable subs in other modules (in B4A it is relevant for classes only).
- The Result parameter name can be changed.
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