How to make a refresh button?

Roma13

I want to show some widgets, but I don't know how many are they. So I made a refresh button and an onclicked slot. When I clicked it , widgets may be added or removed. It worked on the first time, but failed when I click the button.
I have tried update(), repaint(), showNormal, then the exe crashed.
I have tried to delete the old layout, then the exe crashed.
Thank you for your time.

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    dbInitial();
    on_refresh_clicked();
    mainLayout = new QVBoxLayout();
    ui->centralwidget->setLayout(mainLayout);
//    QHBoxLayout * firstline = new QHBoxLayout();
//    firstline->addWidget(ui->firstline);
    mainLayout->addWidget(ui->firstline);
    mainLayout->addLayout(appliance);
////    bool ifShowOffline;
//    QWidget *firstline = new QWidget(ui->centralwidget);
//    QPushButton *refresh = new QPushButton("刷新",firstline);
//    QPushButton *serialPort = new QPushButton("调试串口",firstline);
//    QCheckBox *checkbox_ifShowOffline = new QCheckBox(firstline);
//    checkbox_ifShowOffline->setText("展示不在线设备");
//    QCheckBox *checkbox_ifShowCharts = new QCheckBox(firstline);
//    checkbox_ifShowCharts->setText("展示图表");


//    QGridLayout *layout = new QGridLayout(firstline);
//    layout->addWidget(refresh, 1, 1);
//    layout->addWidget(serialPort,1,2);
//    layout->addWidget(checkbox_ifShowOffline,1,3);
//    layout->addWidget(checkbox_ifShowCharts,1,4);
//    firstline->showNormal();
//    setCentralWidget(firstline);
}

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

void MainWindow::dbInitial(){
    db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName("nilm.db");
    db.open();
    qDebug()<<"数据库连接成功";
}
void MainWindow::on_refresh_clicked()
{
    qDebug()<<"刷新";
//crashed
//    appliance->destroyed();
//    if(!appliance->isEmpty()){
//        delete.appliance;
//    }
    query = new QSqlQuery("select * from nilm where WorkStatu = 1;",db);
    QSqlRecord rec = query->record();
    appliance = new QHBoxLayout();
    while(query->next()){
        rec = query->record();
        //测试先复制，查看是否构造成功
        QString Type = query->value("Type").toString();
        bool WorkStatus = query->value("WorkStatu").toBool();
        int  HealthStatus = query->value("HealthStatu").toInt();
        //新建appliancestatus对象
        ApplianceStatus *applianceTemp = new ApplianceStatus(Type, WorkStatus, HealthStatus,ui->centralwidget);
        appliance->addWidget(applianceTemp);
    }
//following codes lead to crash    
//    ui->centralwidget->showNormal();
//    ui->centralwidget->update();
//    ui->centralwidget->repaint();
}

jsulm

@Roma13 said in How to make a refresh button?:

appliance = new QHBoxLayout();

This layout does not belong to any widget, so what do you expect from adding widgets to it?

Roma13

@jsulm

mainLayout->addLayout(appliance);

I added this layout into mainLayout, still didn't work.