Example 6 [QT simple entry QVariant use, a new method to achieve function overloading]

Outline

QVariant may be used as a container, you can go into other types of values, and then may be removed.
When you want a type, which can store values of different types, can be used QVariant.
QVariant data types that can be saved QString, QImage, QFont, QPixmap, QPoint QT other built-in type, as well as C ++ basic types, such as int, float like. QSettings database module and the module are heavily dependent QVariant class.

Code

1. Press overloading to achieve

For example, I want to write a function can accept different types of parameters, I can use the function overloading to achieve:

main.cpp

#include <QCoreApplication>
#include <QDebug>
#include <QPoint>

//函数重载实现 show()
void show(int i)
{
    qDebug()<<i;
}
void show(float f)
{
    qDebug()<<f;
}
void show(QString s)
{
    qDebug()<<s;
}
void show(QPoint p)
{
    qDebug()<<p;
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    int i=123;
    float f=1.23;
    QString s="nuaa";
    QPoint p(10,20);
    //调用重载函数
    show(i);
    show(f);
    show(s);
    show(p);
    return a.exec();
}

Output:

1. Use to achieve QVariant

main.cpp

#include <QCoreApplication>
#include <QDebug>
#include <QPoint>

//QVariant实现
void Varshow(QVariant v)
{
    if(v.type()==QMetaType::Int){
        int i=v.value<int>();
        qDebug()<<i;
    }
    else if(v.type()==QMetaType::Float){
        float f=v.value<float>();
        qDebug()<<f;
    }
    else if(v.type()==QMetaType::QString){
        QString s=v.value<QString>();
        qDebug()<<s;
    }
    else if(v.type()==QMetaType::QPoint){
        QPoint p=v.value<QPoint>();
        qDebug()<<p;
    }
    else
        qDebug()<<"未定义的传入类型！";
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    int i=123;
    float f=1.23;
    QString s="nuaa";
    QPoint p(10,20);
    //调用函数
    Varshow(i);
    Varshow(f);
    Varshow(s);
    Varshow(p);
    return a.exec();
}

Output:

Although the amount of code seems no difference, but in a medium or large software, especially to the frequent use of different types binary signal slot value is passed, the use QVariant a lot easier than using function overloading.