Begin reversible block

Command group	Flag affected	Reversible	Execute on client	Platform(s)
Constructs	NO	NO	NO	All

Syntax

Description

This command begins a reversible block of commands. All reversible commands enclosed within the commands Begin reversible block/End reversible block are reversed when the method containing this block finishes. However, a reversible block in the $construct() method of a window class reverses when the window is closed not when the method is terminated as is normally the case. Omnis always steps backwards through a reversible block of commands, thus the first command is reversed last.

Reversible blocks let you create subroutines that restore the values of variables, the current record buffer, and so on, to their previous state when the method terminates. Most commands are reversible: those that are not usually involve an irreversible action such as changing the data in an Omnis data file or running another program. Methods called from within a reversible block are not reversed.

Example

# A method can contain more than one block of reversible commands. In this case,

# commands contained within all the blocks are reversed when the method terminates.

 
# All the commands in the following example are reversed when the method containing

# the block is finished

Begin reversible block

  
Disable menu line
 
mMyMenu/5

  
Set current list
 
iMyList

  
Build open window list
 (
Clear list
)

  
Calculate
 
iVar
 as 
0

  
Open window instance
 
wMyWindow

End reversible block
# When this block is reversed:

# The window instance wMyWindow is closed

# iVar returns to its former value

# iMyList is restored to its former contents and definition

# The current list is set to the former value

# Menu line 5 is enabled

 
# The following method hides fields Entry1 and Entry2 and installs the menu mCustomers

Begin reversible block

  
Hide fields
 
Entry1,Entry2

  
Install menu
 
mCustomers

End reversible block
OK message
 (
Icon
)
 {
MCUSTOMERS is now visible
}

# When this method ends, first MCUSTOMERS is removed, then the fields are shown.

 
# In the following example, the current list is iMyList

Begin reversible block

  
Set current list
 
iMyList2

  
Define list
 
fAccounts
.
Code
,
fAccounts
.
Surname
,
fAccounts
.
Balance

  
Set main file
 
fAccounts

  
# Build list  from select table

  
Enter data
End reversible block
# When this method terminates and the command block is reversed, the Main file is reset,

# the former list definition is restored and the current list is restored to iMyList.