Get and Set Methods

[020394]

Anyone can teach me how to implement the get and set method in qt ?

//HEADER FILE
public:
    explicit PatientGui(QWidget *parent = 0);
 
    ~PatientGui();
    QString ID;
 
 
 
    QString getID() const;
    void setID(const QString &value);
 
//CPP FILE
QString PatientGui::getID() const 
{
    return ID;
}
 
void PatientGui::setID(const QString &value)
{
    ID = ui->nric->text();
}
 
//IN THE NEXT GUII WANT TO PASS DATA TO
 
  ui->Patientidentifier->setText(getID());

//HEADER FILE
public:
    explicit PatientGui(QWidget *parent = 0);

    ~PatientGui();
    QString ID;


 
    QString getID() const;
    void setID(const QString &value);

//CPP FILE
QString PatientGui::getID() const 
{
    return ID;
}

void PatientGui::setID(const QString &value)
{
    ID = ui->nric->text();
}

//IN THE NEXT GUII WANT TO PASS DATA TO

  ui->Patientidentifier->setText(getID());

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I gotten this error"error: undefined reference to `Infusion::getID()'"

Can anyone tell me what I did wrong ? I think the way i do iot is wrong , please teach me how to implement it correctly