Delphi in a Nutshell

Name

VarDispProc Variable

Syntax

var VarDispProc: Pointer;

procedure Invoke(Result: PVariant; const Instance: Variant;
  CallDesc: PCallDesc; Params: Pointer); cdecl;
VarDispProc := @Invoke;

Description

VarDispProc points to a procedure that invokes an IDispatch method from a Variant reference. When a Variant refers to a COM server, it is actually storing an IDispatch interface and has the VarType of varDispatch. When your program calls a method or uses a property of the COM server, the Variant object must call the IDispatch.Invoke method. Delphi relies on the VarDispProc procedure to do this.

Result is a pointer to a Variant where a function result should be stored, or it is nil if no result is expected. Instance is the Variant that contains the IDispatch interface invoking the method or property. CallDesc points to a record that describes the method to be invoked, and Params points to an array that describes the method arguments.

Tips and Tricks

• Do not assign nil to VarDispProc. Unlike similar procedure pointers in Delphi, if VarDispProc is nil, Delphi does not have a default behavior, and you get an access violation instead.

• The initial value of VarDispProc points to a procedure that reports runtime error 17 (EVariantError).

• The ComObj unit defines this procedure to handle all the details for you. It also declares the PCallDesc type.

See Also

DispCallByIDProc Variable, Dispinterface Keyword, IDispatch Interface, Interface Keyword, OleVariant Type, Variant Type