qt 下拉框

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功能函数
#include "widget.h"
#include "ui_widget.h"

Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);

    //添加元素
    ui->comboBoxFruit->addItem("please chose fruit");
    ui->comboBoxFruit->addItem("apple");
    ui->comboBoxFruit->addItem("banana");
    ui->comboBoxFruit->addItem("pear");

    //设置前缀后缀
    ui->dSpPrice->setPrefix("$");
    ui->dSpTotal->setPrefix("$");
    ui->spNumber->setSuffix("KG");

    //设置默认值
    ui->spNumber->setValue(5);
    ui->dSpPrice->setValue(5.55);
    ui->dSpTotal->setValue(27.75);

    connect(ui->spNumber,SIGNAL(valueChanged(int)),this,SLOT(spNumberValueChangedSlotFun(int)  ));
    connect(ui->dSpPrice,SIGNAL(valueChanged(double)),this,SLOT(dSpPricevalueChanged(double)));

    //选中更新价格，自动计算总价
    connect(ui->comboBoxFruit,SIGNAL(currentIndexChanged(const QString)),this,SLOT(comboBoxFruitCurrentIndexChangedSlotFun(const QString)    ));

    //重置
    connect(ui->btnReset,SIGNAL(clicked()),this,SLOT(btnResetSlotFun()   ));
}

Widget::~Widget()
{
    delete ui;
}

void Widget::comboBoxFruitCurrentIndexChangedSlotFun(const QString str)
{

    QString str1 = QString("选中了%1").arg(str);
      ui->btnchooseShow->setText(str1);

      if(ui->comboBoxFruit->currentText()=="apple")
      {
         ui->spNumber->setValue(2);
         ui->dSpPrice->setValue(3.8);
         ui->dSpTotal->setValue(ui->spNumber->value()*ui->dSpPrice->value());
      }
      if(ui->comboBoxFruit->currentText()=="pear")
      {
         ui->spNumber->setValue(6);
         ui->dSpPrice->setValue(7.8);
         ui->dSpTotal->setValue(ui->spNumber->value()*ui->dSpPrice->value());
      }
      if(ui->comboBoxFruit->currentText()=="pear")
      {
         ui->spNumber->setValue(3);
         ui->dSpPrice->setValue(5.3);
         ui->dSpTotal->setValue(ui->spNumber->value()*ui->dSpPrice->value());
      }



}

void Widget::spNumberValueChangedSlotFun(int v)
{
    int num = ui->spNumber->value();
    double price = ui->dSpPrice->value();
    ui->dSpTotal->setValue(num*price);
}

void Widget::dSpPricevalueChanged(double v)
{
    int num = ui->spNumber->value();
    double price = ui->dSpPrice->value();
    ui->dSpTotal->setValue(num*price);

}

void Widget::btnResetSlotFun()
{
    ui->spNumber->setValue(0);
    ui->dSpPrice->setValue(0.00);
    ui->dSpTotal->setValue(0.00);
}

头文件
#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACE

class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();

private:
    Ui::Widget *ui;
public slots:
    void comboBoxFruitCurrentIndexChangedSlotFun(const QString);
    void spNumberValueChangedSlotFun(int);
    void dSpPricevalueChanged(double);
    void btnResetSlotFun();
};
#endif // WIDGET_H