title: File not found: mainwindow.obj
body: <ol>
  <li>I created a GUI Application -> QMainWindow</li>
  <li>I added 1 item to the menu + the slot.</li>
  <li>I created a new item -> QDialog</li>
  <li><p>I the slot method i try to show the created dialog but i get this errors:</p>
  
  <p>mainwindow.obj:-1: error: LNK2019: unresolved external symbol "public: __cdecl EditStudentDialog::EditStudentDialog(class QWidget *)" (??0EditStudentDialog@@QEAA@PEAVQWidget@@@Z) referenced in function "private: void __cdecl MainWindow::on_actionNew_triggered(void)" (?on_actionNew_triggered@MainWindow@@AEAAXXZ)</p>
  
  <p>mainwindow.obj:-1: error: LNK2019: unresolved external symbol "public: virtual __cdecl EditStudentDialog::~EditStudentDialog(void)" (??1EditStudentDialog@@UEAA@XZ) referenced in function "private: void __cdecl MainWindow::on_actionNew_triggered(void)" (?on_actionNew_triggered@MainWindow@@AEAAXXZ)</p></li>
  </ol>
  
  <p>This is the main window:</p>
  
  <pre><code>#ifndef MAINWINDOW_H
  #define MAINWINDOW_H
  
  #include &lt;QMainWindow&gt;
  
  namespace Ui {
  class MainWindow;
  }
  
  class MainWindow : public QMainWindow
  {
      Q_OBJECT
  
  public:
      explicit MainWindow(QWidget *parent = 0);
      ~MainWindow();
  
  private slots:
      void on_actionNew_triggered();
  
  private:
      Ui::MainWindow *ui;
  };
  
  #endif // MAINWINDOW_H
  
  #include "mainwindow.h"
  #include "ui_mainwindow.h"
  #include "editstudentdialog.h"
  
  MainWindow::MainWindow(QWidget *parent) :
      QMainWindow(parent),
      ui(new Ui::MainWindow)
  {
      ui-&gt;setupUi(this);
  }
  
  MainWindow::~MainWindow()
  {
      delete ui;
  }
  
  void MainWindow::on_actionNew_triggered()
  {
      EditStudentDialog editDialog;
      editDialog.setModal(true);
      editDialog.exec();
  }
  </code></pre>
  
  <p>This is the dialog ( just an empty one, no controls on it ):</p>
  
  <pre><code>#ifndef EDITSTUDENTDIALOG_H
  #define EDITSTUDENTDIALOG_H
  
  #include &lt;QDialog&gt;
  
  namespace Ui {
  class EditStudentDialog;
  }
  
  class EditStudentDialog : public QDialog
  {
      Q_OBJECT
  
  public:
      explicit EditStudentDialog(QWidget *parent = 0);
      ~EditStudentDialog();
  
  private:
      Ui::EditStudentDialog *ui;
  };
  
  #endif // EDITSTUDENTDIALOG_H
  
  
  #include "editstudentdialog.h"
  #include "ui_editstudentdialog.h"
  
  EditStudentDialog::EditStudentDialog(QWidget *parent) :
      QDialog(parent),
      ui(new Ui::EditStudentDialog)
  {
      ui-&gt;setupUi(this);
  }
  
  EditStudentDialog::~EditStudentDialog()
  {
      delete ui;
  }
  </code></pre>
  
  <p>What am I doing wrong?</p>
  
  <p>EDIT: This is the .pro file</p>
  
  <pre><code>QT       += core gui
  
  greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
  
  TARGET = GUI1
  TEMPLATE = app
  
  
  SOURCES += main.cpp\
          mainwindow.cpp \
      editstudentdialog.cpp
  
  HEADERS  += mainwindow.h \
      editstudentdialog.h
  
  FORMS    += mainwindow.ui \
      editstudentdialog.ui
  </code></pre>
  
  <p>PS: I tried to clean the project and then build it but still the same issue.</p>
  
  <p>EDIT 2: I am using Qt Creator 2.7 with Qt 5.0.2</p>