Write your own dialogs

Let's built a custom dialog, that works just like the C++ Builder's dialog components.
But we don't want to develop a full blown component (with published properties and methods for creation and destroying, and more complicated stuff...) because that would be a bit overkill.

Let's suppose that you want a simple dialogbox that looks like the one above. You want to call that dialog from your code by clicking Button1 on your main form:

void __fastcall TForm1::Button1Click(TObject *Sender)
{
  if (UserDialog->Execute())
    Label1->Caption = "Username: " + UserDialog->UserName;
  else  
    Label1->Caption = "Error: no username was entered";
}

Building the example

1. Add a new form to your project and call it UserDialog.
2. Save the new unit as UserDlg.
3. Set the form's Caption to 'Please enter your username:' and set its BorderStyle property to bsDialog.
4. Add three components:
   - a TEdit; clear its Text property.
   - a TBitButton; set its property Kind to bkOK.
   - a second TBitButton; set its property Kind to bkCancel.
5. In UserDlg.h, add two lines under public: as follows:

   public:		    // User declarations
     String UserName;
     __fastcall TUserDialog(TComponent* Owner);
     bool Execute();

6. In UserDlg.cpp, add the following function implementation at the end of the unit:

   bool TUserDialog::Execute()
   {
     UserDialog->ShowModal();
     return (ModalResult == mrOk);
   }
   

7. Through the Object Inspector, create an event handler for OnClick of Button1 and complete it as follows:

   void __fastcall TUserDialog::BitBtn1Click(TObject *Sender)
   {
     UserName = Edit1->Text;
   }

8. Select Unit1.cpp and switch to Design mode.
9. In the menu, select File / Use unit... and select UserDlg.cpp
10. Save all and test your program.

That's all! But how does your program's magic work?

• The function Execute shows the UserDialog form in a "modal" way, that means: the window will open on top of the other window(s) and the application does not continue before UserDialog is closed.
• If the user clicks the OK button, the dialog is automatically closed and our Execute function returns True.
• If the Cancel button is clicked, the dialog also closes, but we receive False.
• Also when the UserDialog is closed in another way, we get False.
• Finally, the text of the edit-box is copied to the public variable UserName, from where other units can access it.