The C++ Builder (and Turbo C++) TForm class ('Form' from now on) can be created either statically or dynamically.

View the code of 'Create Forms Dynamically' in plain text

When to consider creating Forms dynamically

Consider creating Forms dynamically when:

you want to create multiple instances of the same Form
you've added additional constructor parameters
you want to have a hierarchy in your Forms
you want to create Forms one by one
you want to create Forms in idle time
you want Forms to be created by a seperate thread

Do's and don'ts when creating Forms dynamically

When you want to dynamically create a Form

do make it an 'Available Form' ('Project | Options | Forms'), instead of an automatically created Form
do make a Form refer to itself as 'this', instead of using, for example 'Form1'

How to create a Form dynamically

A Form can be created dynamically as follows:


//Put this line among the other #includes

#include <memory>



//Your method

void __fastcall TFormMain::YourMethod()

{

  std::auto_ptr<TFormDynamic> f(new TFormDynamic(this));

  f->ShowModal();

}

Sure you can use a plain pointer, but then don't forget to delete it. And if you don't want to forget to delete this pointer (among others), use a std::auto_ptr.

Instead of passing 'this', you might sometimes consider passing '0' as an argument to the constructor of TFormDynamic.

Communicate with the creator of a Form

In the code snippet above, the Form called TFormDynamic is constructed using a pointer to the TFormMain Form. This enables the newly created TFormDynamic to be potentially able to communicate with the TFormMain.

Communicate with the creator of a Form in the constructor only

The constructor of a Form takes as an argument the TComponent that has created it. Therefore, you can easily use it locally:


//Put this line among the other #includes

#include <cassert>



__fastcall TFormDynamic::TFormDynamic(TComponent* Owner)

: TForm(Owner)

{

  TFormMain * const formMain = dynamic_cast<TFormMain>(Owner);

  assert(formMain!=0); //Assume cast succeeded



  //Use formMain

}

Communicate with the creator of a Form using a member variable

You can also make the TFormMain pointer a member variable of TFormDynamic:


//UnitFormDynamic.h



//A forward declaration

//Put it after the #includes and before the next line

class TFormMain;



class TFormDynamic : public TForm

{

__published: // IDE-managed Components

//Stuff

private: // User declarations

TFormMain * const mFormMain;

public: // User declarations

__fastcall TFormDynamic(TComponent* Owner);

};



//UnitFormDynamic.cpp



//Put this line among the other #includes

#include <cassert>



__fastcall TFormDynamic::TFormDynamic(TComponent* Owner)

: TForm(Owner),

mFormMain(dynamic_cast<TFormMain>(Owner)

{

assert(mFormMain!=0); //Assume cast succeeded



//Use mFormMain

}

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