There are two optional parameters that are supported by all sections whose entries are separated into parameters except for [Languages], [Types], [Components] and [Tasks]. These are:

BeforeInstall

The name of a function that is to be called once just before an entry is installed. The function must either be a custom function in the [Code] section or a support function.

May include a comma separated list of parameters that Setup should pass to the function. Allowed parameter types are String, Integer and Boolean. String parameters may include constants. These constants will not be automatically expanded. If you want to pass an expanded constant, there's one special support function that may be called from within a parameter list for this: ExpandConstant.

Example:

[Files]
Source: "MYPROG.EXE"; DestDir: "{app}"; BeforeInstall: MyBeforeInstall
Source: "A\MYFILE.TXT"; DestDir: "{app}"; BeforeInstall: MyBeforeInstall2('{app}\A\MYFILE.TXT')
Source: "B\MYFILE.TXT"; DestDir: "{app}"; BeforeInstall: MyBeforeInstall2('{app}\B\MYFILE.TXT')
Source: "MYPROG.CHM"; DestDir: "{app}"; BeforeInstall: Log('Before MYPROG.CHM Install')

AfterInstall

The name of a function that is to be called once just after an entry is installed. The function must either be a custom function in the [Code] section or a support function.

May include a comma separated list of parameters that Setup should pass to the function. Allowed parameter types are String, Integer and Boolean. String parameters may include constants. These constants will not be automatically expanded. If you want to pass an expanded constant, there's one special support function that may be called from within a parameter list for this: ExpandConstant.

Example:

[Files]
Source: "MYPROG.EXE"; DestDir: "{app}"; AfterInstall: MyAfterInstall
Source: "A\MYFILE.TXT"; DestDir: "{app}"; AfterInstall: MyAfterInstall2('{app}\A\MYFILE.TXT')
Source: "B\MYFILE.TXT"; DestDir: "{app}"; AfterInstall: MyAfterInstall2('{app}\B\MYFILE.TXT')
Source: "MYPROG.CHM"; DestDir: "{app}"; AfterInstall: Log('After MYPROG.CHM Install')

All BeforeInstall and AfterInstall functions must not have a return value.

A BeforeInstall or AfterInstall function isn't called if Setup already determined the entry it shouldn't be processed.

A BeforeInstall or AfterInstall function for a [Files] section entry using a wildcard is called once per file matching the wildcard. Use CurrentFileName to check for which file the function is called.

Here is an example of a [Code] section containing the functions used above. Functions CurrentFileName and Log are support functions and therefore not included in this [Code] section.

[Code]
procedure MyBeforeInstall();
begin
  MsgBox('About to install MyProg.exe as ' + CurrentFileName + '.', mbInformation, MB_OK);
end;

procedure MyBeforeInstall2(FileName: String);
begin
  MsgBox('About to install ' + FileName + ' as ' + CurrentFileName + '.', mbInformation, MB_OK);
end;

procedure MyAfterInstall();
begin
  MsgBox('Just installed MyProg.exe as ' + CurrentFileName + '.', mbInformation, MB_OK);
end;

procedure MyAfterInstall2(FileName: String);
begin
  MsgBox('Just installed ' + FileName + ' as ' + CurrentFileName + '.', mbInformation, MB_OK);
end;