Delphi XE3 and Crystal Reports

Question

Some time ago (actually almost 5 years ago) there was an example posted here that showed a method of displaying Crystal Reports in Delphi 2007 using the ActiveX report viewer. I have found that it also works in Delphi XE3. The snippet I have a question about is as follows:

for i := 1 to oRpt.Database.Tables.Count do begin
oRpt.Database.Tables[i].ConnectionProperties.Item['User ID'] := 'username';
oRpt.Database.Tables[i].ConnectionProperties.Item['Password'] := 'password';
end;

My question: since oRpt is a variant and not typed, how do I find the properties of the report viewer and set their values inside the proc that displays or prints the report ??

Answer 1

Read the documentation. :-)

There are two ways to connect to an ActiveX server: at compile-time (early binding) or at run-time (late binding). There's [an article at MSDN that explains in more detail.

Early binding is what is used when you use typed variables (such as using the TWordApplication or TExcelApplication from the component palette). The type library is used to determine what types and interfaces are supported, and methods can be looked up using a DispInterface from the v-table; the compiler can then validate that functions exist and check for typos and such, and figure out what's available for Code Completion and Code Insight).

Accessing an ActiveX server by way of a variant (as your code snippet demonstrates) is late binding. Nothing is known to the compiler until the code is actually executed, at which point the methods are attempted to be called via an IDispatch interface, and it either succeeds or fails at that point. Because the compiler knows nothing about what your variant might contain, there's no way to know at design or compile time what methods and types are available.

Because your code is using late binding, there's no way to know what properties might be available except for reading the documentation (or trial and error, of course, which isn't really an option). (The other alternative is to use early binding, if there's a type library available for the ActiveX server, at which point you stop using a variant and switch to an interface that the compiler can use to determine what's available to you.)