[solved]class doesn't name a type

[mehdi.nine]

Hi, I have to class, USB and MainForm.
in USB class i want to have an object of Mainform class but it has following error:
@
C:\Users(Mahdi)\Documents\QT\untitled1\usb.h:28: error: 'MainForm' does not name a type
@
this is USB.h
@
#include "mainform.h"
using namespace std;
class USB:public QThread
{

private:

int Digital_Packet_Count;
int Analog_Packet_Count;
int TAkhasosi_Packet_Count;
ContentControl *Temp_Content;
MainForm *m;
.
.
.
@
this is MainForm class:
@
namespace Ui {
class MainForm;
}

class MainForm : public QWidget
{
Q_OBJECT

public:

QList<QWidget*> All_Images;
QList<QMovie*> All_Gif;
explicit MainForm(QWidget *parent = 0);
~MainForm();

@
what is problem?(ContentControl is another class that i have an object from it in USB class but it has no problem)

[koahnig]

Try
@
Ui::MainForm *m;
@

[mehdi.nine]

i did it but has following error:
@
C:\Users(Mahdi)\Documents\QT\untitled1\usb.h:22: error: 'MainForm' in namespace 'Ui' does not name a type
@

[dbzhang800]

Hi, note that, QWidget and subclass of it can only be used main thread.

[mehdi.nine]

Hi, can you explain more?

[SGaist]

Hi,

Short version: QWidget and QWidget based classes can only be used from the GUI thread. The one that is started when you call app.exec();

You can't create and use widgets from other threads

[mehdi.nine]

thanks. so i can't use from MainForm Object in USB class any way?

[SGaist]

No,

You should have your class USB do all the handling it needs to do (I suppose it's low level stuff), give it an interface where you can connect a GUI on it and keep the two things separated.

It will make your design cleaner keeping either responsibilities separated

[mehdi.nine]

thanks for all replies.
i found the problem. i MainForm class i include usb.h and in usb.h i include MainForm.h. when i delete usb.h from MainForm problem has solved.