Problems with this->CreateGraphics()

  • Thread starter Thread starter saunderl
  • Start date Start date
S

saunderl

Hello Everyone,

I'm trying to just play with managed VC++. I just want to draw a box
on the form when it is clicked. Here is my click event handler

System::Void Test_Click(System::Object^ sender, System::EventArgs^ e)

{
// Create a Graphics object for the Control.
Graphics* g = this->CreateGraphics() ;

g->DrawRectangle(gcnew Pen(Color::Green, 1.0), 1, 1, 100, 100);
}

Trying to create a graphics object this way (Graphics* g =
this->CreateGraphics();)
I get this error:

Error 1 error C3699: '*' : cannot use this indirection on type
'System::Drawing::Graphics' c:\documents and settings\saul01\my
documents\visual studio
2005\projects\cc2\managedxp\managedxp\Test.h 77


Trying to create a graphics object this way (Graphics g =
this->CreateGraphics();)

Error 1 error C3767: 'System::Drawing::Graphics::Graphics': candidate
function(s) not accessible c:\documents and settings\saul01\my
documents\visual studio
2005\projects\cc2\managedxp\managedxp\Test.h 77


I'm using VS2005 and all the other code was generated by Visual Studio.

Thanks for the help, L. Lee Saunders
 
You can only draw your box while in the Paint event of your form. Thus, you
need something along the lines of (typed from memory, so might be a little
off):

void OnPaint( Object^, PaintEventArgs^ e ) override
{
Graphics graphics = e->Graphics ;
graphics->DrawRectangle(...) ;
}

However, the error you got is becuase you're mixing syntaxes. '*' is the
pointer character in 'old style' syntax, you need to use '^' in the new
syntax. And note you're (trying to) using both at the same time! : )

[==P==]
 
Hello Everyone,

Further more, I cannot even create variable of type Graphics even in:

System::Void Test_Paint(System::Object^ sender,
System::Windows::Forms::PaintEventArgs^ e)

I get the same errors. I can though draw using:

e->Graphics->DrawRectangle(gcnew Pen(Color::Green, 1.0), 1, 1, 100,
100);

Thanks for the help, L. Lee Saunders
 
correction:

void OnPaint( Object^, PaintEventArgs^ e ) override
{
Graphics^ graphics = e->Graphics ; // important!!! :)
graphics->DrawRectangle(...) ;
}

Peter Oliphant said:
You can only draw your box while in the Paint event of your form. Thus,
you need something along the lines of (typed from memory, so might be a
little off):

void OnPaint( Object^, PaintEventArgs^ e ) override
{
Graphics graphics = e->Graphics ;
graphics->DrawRectangle(...) ;
}

However, the error you got is becuase you're mixing syntaxes. '*' is the
pointer character in 'old style' syntax, you need to use '^' in the new
syntax. And note you're (trying to) using both at the same time! : )

[==P==]

Hello Everyone,

I'm trying to just play with managed VC++. I just want to draw a box
on the form when it is clicked. Here is my click event handler

System::Void Test_Click(System::Object^ sender, System::EventArgs^ e)

{
// Create a Graphics object for the Control.
Graphics* g = this->CreateGraphics() ;

g->DrawRectangle(gcnew Pen(Color::Green, 1.0), 1, 1, 100, 100);
}

Trying to create a graphics object this way (Graphics* g =
this->CreateGraphics();)
I get this error:

Error 1 error C3699: '*' : cannot use this indirection on type
'System::Drawing::Graphics' c:\documents and settings\saul01\my
documents\visual studio
2005\projects\cc2\managedxp\managedxp\Test.h 77


Trying to create a graphics object this way (Graphics g =
this->CreateGraphics();)

Error 1 error C3767: 'System::Drawing::Graphics::Graphics': candidate
function(s) not accessible c:\documents and settings\saul01\my
documents\visual studio
2005\projects\cc2\managedxp\managedxp\Test.h 77


I'm using VS2005 and all the other code was generated by Visual Studio.

Thanks for the help, L. Lee Saunders
Click to expand...
Click to expand...
 
Just to emphasize, this is not proper syntax:

Graphics* graphics ;

this is:

Graphics^ graphics ;

[==P==]
 
Thanks Peter!

Why oh why does every example of Microsofts uses the * ?

I've seen examples with the ^ but I've never seen a discussion on what
it is or used for.

Thanks again, Lee
 
Why oh why does every example of Microsofts uses the * ?
Click to expand...

There are two "dialects" of C++ that can be used to target the .Net
environment. The older is called Managed Extensions for C++ aka MC++. The
newer one - just out last month with VS 2005 - is called C++/CLI (common
language infrastructure) or something.

MC++ uses pointers syntax _both_ for addresses of native objects and for the
GC handles to managed objects.

C++/CLI stresses the difference between pointer and handle by using the
circumflex (^).
I've seen examples with the ^ but I've never seen a discussion on what
it is or used for.
Click to expand...

You can start reading here

http://msdn.microsoft.com/msdnmag/issues/05/02/PureC/

and then google for

C++/CLI

Regards,
Will
 
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