Incorrect parameter for custom event handler

c++ builder

    Sponsored Links


  • 1. message procedure
    What do you do with something like this: procedure WMSetCursor(var Message: TWMSetCursor); message WM_SetCursor; I have no clue how to deal with this to convert it to CBuilder. ~ JD
  • 2. Component's icon in runtime
    Hi, I'm looking for a way to retrieve in runtime (by the shipped program) the component's icon of the installed package as it appears on the IDE. It's for fault logging purpose, using the icon to indicate the type of control. Any idea? Tks & Rgds, Martin
  • 3. override - dynamic - virtual
    In some components written in Delphi, one might see the keyword override at the end of the proceedure definition. I'm uncertain as to what it (override) actually means and how it is reflected when writing a component in CBuilder. When I see 'override', does the function actually subplant the the default block of code? Is the default block of code executed ONLY if the function calls it's inherited method? As for how 'override' translate to CBuilder, is it enough to simply declare the function to override it? For example: protected: DYNAMIC void __fastcall MouseDown(TMouseButton Button, TShiftState Shift, int X, int Y); Are all events that respond to system notifications DYNAMIC in CBuilder component writing? I'm also confused by this example: Delphi: procedure BoundsChanged; override; CBuilder: virtual void __fastcall BoundsChanged(); The problem is in CBuilder it's defined as virtual which totally clouds the issue of when a Delphi function is virtual and how to deal with it in CBuilder. The same goes for dynamic Delphi functions. Are all methods that respond to Windows messages virtual in CBuilder component writing? ~ JD
  • 4. How to paint a border.
    Hi everyone, I am making a new component that inherits from TCustomControl. How can I paint a border?. I already set the 'BorderWidth' property to 1 to separate the client area. Thanks, Hernan Diaz

Incorrect parameter for custom event handler

Postby Myles Rippenhagen » Wed, 26 Oct 2005 02:43:50 GMT


I have created several custom components and generally have had great 
success with them, but I am currently running into a problem where when I 
double-click on a published custom event (on the "Events" tab of the "Object 
Inspector" in the IDE), the inserted method declaration contains the wrong 
variable name.  The signature matches another, similar custom event, and it 
seems to be picking up the parameter name from this other definition.  I 
have double-checked that I am referencing the correct typedef in the 
definition of my custom component and I didn't see any problem.  I am using 
BCB6 Enterprise on WinXP.  Following are the important bits of the code.

typedef void __fastcall (__closure *BeforePostEvent) (TObject* Sender, bool 
typedef void __fastcall (__closure *OnPutToDatabaseEvent) (TObject* Sender, 
bool &DoDefault);
   OnPutToDatabaseEvent FOnPutToDatabaseEvent;
   __property OnPutToDatabaseEvent OnPutToDatabase = 
{read=FOnPutToDatabaseEvent, write=FOnPutToDatabaseEvent};

When I double-click on the "OnPutToDatabase" event in the IDE, the inserted 
code labels the bool parameter "CanPost" instead of "DoDefault".  It appears 
to just pick up the first typedef with a matching signature instead of using 
the typdef that I specified.

Any suggestions??

Re: Incorrect parameter for custom event handler

Postby Remy Lebeau (TeamB) » Wed, 26 Oct 2005 03:12:24 GMT

That is a long-standing known issue.  The OI matches events by signatures
only, not names.  You have two different events that have the exact same
signature (return value, calling convention, parameter data types, and
parameter ordering).  The OI always generates code using the first event
type that matches the required signature.

That is exactly why you are seeing what you have described.  There is
nothing you can do to prevent the OI from behaving that way.  You will just
have to change the signature of one of your events so that they no longer
match each other.

The OI does not care about typedefs.  It only cares about signatures.


Similar Threads:

1.Why event handler first parameters are incorrect

I noticed that DataGridView CellValidated() and other event handler first 
parameter is object:


        void Grid_CellValidated(object sender, DataGridViewCellEventArgs e) 

Why ? Correct signature must be

void Grid_CellValidated(DataGridView sender, DataGridViewCellEventArgs e) {


2.Custom event handler

Hello, all.  I am trying to develop my first component and I am trying to
figure something out.  I created a MouseMove event handler for my component
(TMyComponent::MouseMove) and it works fine.  I added my component to a new
project (TMyComponent *MyComponent1) and I want perform a task in the
MyComponent1MouseMove event.  My problem is that the TMyComponent::MouseMove
function is executing, but the TForm1::MyComponent1MouseMove function is
not.  I set the OnMouseMove event to MouseMove for the MyComponent1
instance, but it still only calls the component handler, not the custom
handler.  Why won't it call my custom handler?  Actually, I will need both
functions to execute.  Will I need to explicitly call
TMyComponent::MouseMove() from within the TForm1::MyComponent1MouseMove
function to get both to execute?  Any feedback will be greatly appreciated.



3.Custom event handlers in .NET Winforms

4.Custom Event Handler

I am getting an error down below, this same code works in VB, what gives?

private void Form1_Load(object sender, System.EventArgs e)


System.Windows.Forms.LinkLabel l = new System.Windows.Forms.LinkLabel();

FileSystemWatcher watcher = new FileSystemWatcher();

watcher.Path = @"C:\TempFolder";

watcher.Filter = "*.txt";

//error here: Cannot implicitly convert type System.EventHandler to

watcher.Created += new System.EventHandler(OnCreated);

watcher.EnableRaisingEvents = true;


private void OnCreated(object sender, System.EventArgs e)




5.Custom event handlers and searching a listview

6. Passing in a OnMouseDown/OnMouseUp event handler as a parameter of a function

7. How to pass more than two parameters in the event handler

8. TADODataset.Parameters.Refresh results in incorrect parameter names

Return to c++ builder


Who is online

Users browsing this forum: No registered users and 93 guest