Easy question. How I can modify INSTALLDIR in my project

[Hazard]

Hi, community.

Easy question. How I can modify "INSTALLDIR" from a dialog windows?
I have downloaded this example here:

http://community.flexerasoftware.com/showthread.php?t=201283


I added to the button "Next" (dialog "InstallWelcome") an additional action, "DoAction" = "DisplayINSTALLDIR"

function DisplayINSTALLDIR(hMSI)
    STRING szInstDir;
    STRING szInstDir2;
    NUMBER nvCount;
    INT result;
begin
	nvCount = MAX_PATH;
	
	MsiGetProperty(hMSI, "INSTALLDIR", szInstDir, nvCount);;

	SprintfBox(INFORMATION, "INSTALLDIR", szInstDir);	
	
	szInstDir = "c:\\Projects";
	
	result = MsiSetProperty(hMSI, "INSTALLDIR", szInstDir);
	
	result = MsiGetProperty(hMSI, "INSTALLDIR", szInstDir2, nvCount);
	
	SprintfBox(INFORMATION,"Deferred Execution", szInstDir2);		
	
end;

But, unfortunately, the result is very strange. The MessageBox shows empty value.

So, I think I have some fundamental misunderstanding. Please, help me.

How does it possible to change "INSTALLDIR" value?

The project is attached...

[Hazard]

Some strange things. Now the ShowMessage shows right value.

[jforst]

Make sure to set nvcount before each call to to MsiGetProperty.

[Hazard]

I think the problem was with the uncompiled script. It seems that you will debug the script very carefully, always compile it before debugging, because sometimes I saw the values of my constants that were modified before.