Android Question ExternalStorage: Copy to USB with progress on main UI thread

public Sub CopyToUSB(sourceDir As String, sourceFile As String, dest As String) 
    dest = ProcessPath(dest)
        
    Dim inStream As InputStream = File.OpenInput(sourceDir, sourceFile)
    Dim totalSize As Long = File.Size(sourceDir, sourceFile)
    
    Dim outFile As ExternalFile = FindDeepFile(Storage.Root, dest, True)
    Dim outStream As OutputStream = Storage.OpenOutputStream(outFile)
    
    CopyStreams(inStream, outStream, totalSize)
    
    inStream.Close
    outStream.Flush
    outStream.Close
    
    OnCopyComplete(sourceDir & "/" & sourceFile, dest)
End Sub

Private Sub CopyStreams(in As InputStream, out As OutputStream, totalSize As Long)
    Dim buffer(FILE_COPY_BUFFER_SIZE) As Byte
    Dim read As Int = 0
    
    Dim lastProgress As Int = -1
    Dim bytesWritten As Long  = 0
    Do While(True)
        read = in.ReadBytes(buffer, 0, buffer.Length)
            If read = -1 Then
            Exit
        End If       
         out.WriteBytes(buffer, 0, read)
        bytesWritten = bytesWritten + read       
        Dim progress As Int = (bytesWritten / totalSize) * 100
        If progress > lastProgress Then
            lastProgress = progress           
            OnCopyProgress(progress)
        End If       
       Loop   
End Sub

Private Sub OnCopyProgress(progress As Int)    
    CallSub2(module, eventName  & "_CopyProgress", progress)
End Sub

Sub ES_CopyProgress(progress As Int)
    CallSubDelayed2("Upload","DisplayCopyProgress", progress)
End Sub

Sub DisplayCopyProgress(progress As Int)
    Sleep(0)
    Log("USB Copying " & progress)
    lbl_Process_Status.Text = "Progess: " & progress
End Sub