(C++ VCL) TForm

The Component you put all others on. Without any others on it, it is an empty window. Can be found in Forms.hpp.

TForm related functions

GetFormImage, obtain a TBitmap from a TForm

Multiple TForms

There are multiple options when you want to develop an application with multiple forms. You can use Auto-created Forms (default) or create them dynamically yourself. Also you can choose between using normal Forms or use MDI Parents and MDI Childs. MDI is an abbreviation for 'Multiple Document Interface'.

An Auto-created Form showing another auto-created Form

To have multiple (non-parent) TForms in your program, do (using default names):

Create an VCL Application (called Project1 with Unit1 and Form1)
Create a new Form (called Unit2 and Form2)
Save all in the same directory under their default names
Select Form1
Select 'Project | Add to Project | Unit2.cpp'
Select 'File | Include Unit Hdr | Unit2'

Now you can type, e.g. under an OnClick event:

  Form2->Show();

An Auto-created MDI Form showing another auto-created MDI Child

Start a new VCL Application
Set the Form Name to FormParent.
Set FormParent's FormStyle to fsMDIForm.
Save this Form as UnitFormParent.cpp.
Create a new Form called FormChild
Set FormChild's FormStyle to fsMDIChild
Save this Form as UnitFormChild.cpp
Select FormParent
Select 'Project | Add to Project | UnitFormChild.cpp'
Select 'File | Include Unit Hdr | UnitFormChild'

Now you can type, e.g. under an OnClick event:

  FormChild->Show();

Note that this is not the standard use of an MDI application, as we only have one single Child, which only has one instance. But the Child DOES have different behaviour compared to standard Forms.

An Auto-created MDI Form showing multiple dynamically-created MDI Childs

Start a new VCL Application
Set the Form Name to FormParent.
Set FormParent's FormStyle to fsMDIForm.
Save this Form as UnitFormParent.cpp.
Create a new Form called FormChild
Set FormChild's FormStyle to fsMDIChild
Save this Form as UnitFormChild.cpp
Select FormParent
Select 'Project | Add to Project | UnitFormChild.cpp'
Select 'File | Include Unit Hdr | UnitFormChild'
Do 'Project | Options | (tab) Forms', then remove 'FormChild' from the Auto-create list

Creating an instance of a Child can be done like this:

  //Somewhere in code of FormParent, e.g. under an OnClick Event
  TFormChild * child = new TFormChild(this);
  //Code
  delete child;

Or using a auto_ptr:

  //Headers
include <memory>


  //Somewhere in code of FormParent, e.g. under an OnClick Event
  std::auto_ptr<TFormChild> child(new TFormChild(this));
  //Code

But this simple code is not enough, as you probably want to keep the Child Forms on the Parent Form. So you could use a vector storing these child pointers. I use the shared_ptr for this:

//UnitFormParent.h
//Add these headers
include <vector>

include <boost/shared_ptr>


//Add to the private section of the class declaration:
std::vector<boost::shared_ptr<TFormChild> > mChilds;

Then add to FormParent's definitions:

//A button for creating a new Child
void __fastcall TFormMain::ButtonNewClick()
{
  mChilds.push_back(boost::shared_ptr<TFormChild>(new TFormChild(this)));
  //Optionally: (you'll need to add a Label to the Child)
  mChilds.back()->Label1->Caption = "Child #" + IntToStr(Tag);
  ++Tag;
}
//---------------------------------------------------------------------------
//A button for removing a Child
void __fastcall TFormMain::ButtonDeleteClick()
{
  if (!mChilds.empty()) mChilds.pop_back();
}
//---------------------------------------------------------------------------

Transparency

Making a Form transparent is easy. First set the AlphaBlend property to true. Then the AlphaBlendValue determines the transparency. An AlphaBlendValue of 0 denotes total transparence (you won't see it anymore), an AlphaBlendValue of 255 denotes the standard non-transparency.

Custom shape

Here's a simple example showing to change your Form's shape:

__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
  HRGN h1 =CreateEllipticRgn(0,0,100,100);
  HRGN h2 =CreateEllipticRgn(90,0,190,100);
  HRGN h3 =CreateEllipticRgn(180,0,280,100);
  CombineRgn(h1,h1,h2,RGN_OR);
  CombineRgn(h1,h1,h3,RGN_OR);
  SetWindowRgn(Handle,h1,true);
  DeleteObject(h1);
  DeleteObject(h2);
  DeleteObject(h3);
}

'TForm' Links

C++ CLX TForm
Pascal VCL TForm
Pascal CLX TForm

Code links

last edited (December 23, 2006) by bilderbikkel, Number of views: 3271, Current Rev: 10 (Diff)

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