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(C++ VCL) TForm

VCL data type for a form, the Component you put all others on. Without any others on it, it is an empty window. Can be found in the header file Forms.hpp.

For code snippets using TForm, go to the VCL graphics code snippets page

Page overview

Page overview 1

Multiple TForms 1

An Auto-created Form showing another auto-created Form 1

An Auto-created MDI Form showing another auto-created MDI Child 1

An Auto-created MDI Form showing multiple dynamically-created MDI Childs 2

Get a TForm in a TForm 3

Transparency 3

TForm troubles 3

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):

*        Start a new VCL Application (called Project1 with Unit1 and Form1)

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 std::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 std::vector storing these child pointers. I use the boost::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();

}

//---------------------------------------------------------------------------

Get a TForm in a TForm

You can get a TForm in a TForm as if it were a TPanel. Go to the page 'Get a TForm in a TForm'

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.

TForm troubles

Never change the TForm constructor to the following:

__fastcall TFormParent::TFormParent(TComponent* Owner, const int i) //Don't do this!

: TForm(Owner)

//Rest of the code

{

//Rest of the code

}

This will (strangely) result in a stack overflow.

One workaround is to use AnsiString instead of an integer:

__fastcall TFormParent::TFormParent(TComponent* Owner, const AnsiString i)

: TForm(Owner)

//Rest of the code

{

//Rest of the code

}

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