Link2019: Unresolved external symbol for calling dialog qt - c++

Question

I'm kind of new to QT programming, and I encountered this strange error when I was trying to have the program open a new dialog that I have created with a press of a button.
I am trying to open table.ui, robotdance.ui, and graph.ui from scouting.ui by pressing a button. In scouting.cpp:
table *teamtable = new table(this); teamtable->show();
I have included the header files for the .ui's into the scouting.cpp, but it's giving me this error:
scouting.obj:-1:
error: LNK2019: unresolved external symbol "public: __thiscall graph::graph(class QWidget *)" (??0graph##QAE#PAVQWidget###Z) referenced in function "private: void __thiscall Scouting::on_actionGraphs_triggered(void)" (?on_actionGraphs_triggered#Scouting##AAEXXZ)
Two more errors are shown which are similar to this one.
Why is this happening? I followed this guy's tutorial and did what he did but he doesn't seem to get any errors.
scouting.cpp:
http://pastebin.com/NEEu9jmM
table.h:
http://pastebin.com/BMDCkcwJ
table.cpp
is in the additional comment section, since I can't post more than 2 links.

Answer 1

I believe you are building your application on windows. I suspect that visual studio project files are not updated with the added files, and that is causing the problem. Just delete the visual studio build folder, and rebuild. It will work fine.

Answer 2

Usually there are two possible reasons for this:
A) You did not add graph.cpp (and other .cpp files) to your .pro file
B) Your header file looks somewhat like this
class graph : public QWidget
{
public:
graph( QWidget* parent );
~graph();
...
}
but your source file (.cpp) does not contain this:
#include "graph.h"
graph::graph( QWidget* parent ) :
QWidget( parent )
{
...
}
graph::~graph()
{
...
}

Answer 3

This is an error from linker that can not link all of the object files together.
your header and source files added to your project?
if you are using any library in Qt, you might add them to your project's .pro file (for example: QT += core gui webkitwidgets network)
add all of library directives of classes that you are using in your codes.
(such as #include <QDialog>)
Don't forget to delete all of compiler generated output directory from your project's path, take attention DO NOT remove your project's source directory, after delete project's output directory first right click on your project and click Run qmake then build your project.