QListWidget实现内部拖动排序功能

1.需求

将QListWidget有很多的任务，需要拖动任务，手动进行排序，并且需要保存拖动之后的顺序，软件重新打开要是修改之后的顺序；

（1）继承QListWidget，重写一个QListWidget自定义类

#ifndef DROPLISTWIDGET_H
#define DROPLISTWIDGET_H

#include <QListWidget>
#include <QDropEvent>
class DropListWidget : public QListWidget
{
    Q_OBJECT

public:
    DropListWidget(QWidget *parent);
    ~DropListWidget();
    void dropEvent(QDropEvent *event);
signals:
    void signalDropEvent(QListWidgetItem* pItem);
private:
    
};

#endif // DROPLISTWIDGET_H

#include "DropListWidget.h"

DropListWidget::DropListWidget(QWidget *parent)
{
    this->setParent(parent);
}

DropListWidget::~DropListWidget()
{

}

void DropListWidget::dropEvent(QDropEvent *event)
{
    QListWidget::dropEvent(event);//保留QListWidget拖拽功能
    QListWidgetItem * pItem = currentItem();
    if (pItem)
    {
        emit signalDropEvent(pItem);//发出信号，保存排序
    }
}

connect(ui.listWidget, &DropListWidget::signalDropEvent, this, &VideoCollsionTaskList::handleDropEvent);

（2）通过本地数据库保存拖动后的时间，拖到第一个，时间变为第二个时间减一天，拖到两个之间时，时间变为前后两个的平均值，拖到最后一个，则是将时间设置为当前时间，新插入的放在列表最后，时间是当前时间，这样就可以通过时间来排序，软件重新打开之后，按照时间正序去查询数据库，然后按照时间顺序添加到列表中。

void VideoCollsionTaskList::handleDropEvent(QListWidgetItem* pItem)
{
    if (pItem==NULL)
    {
        return;
    }
    CollisionListItem * pCurrentTask =(CollisionListItem *) ui.listWidget->itemWidget(pItem);
    if (pCurrentTask==NULL)
    {
        return;
    }
    
    VideoCollisionTask cuTask=pCurrentTask->GetTaskInfo();
    QString strCurrentTime = cuTask.createTime;
    int row=ui.listWidget->row(pItem);
    int rowCount = ui.listWidget->count();
    if (rowCount==1)//只有一个不变
    {
        return;
    }
    QListWidgetItem* pNext = NULL;
    QListWidgetItem* pPrevious = NULL;
    if (row==0)//拖到第一个
    {
        pNext=ui.listWidget->item(1);
        if (pNext)
        {
            CollisionListItem * pNextTask=(CollisionListItem *) ui.listWidget->itemWidget(pNext);
            QString strNextTime = pNextTask->GetTaskInfo().createTime;
            strCurrentTime=QDateTime::fromString(strNextTime, "yyyyMMdd hh:mm:ss").addDays(-1).toString("yyyyMMdd hh:mm:ss");//减一天
        }
    }
    else if (row==rowCount-1)//拖到最后一个
    {
        pPrevious= ui.listWidget->item(row-1);
        if (pPrevious)
        {
            strCurrentTime = QDateTime::currentDateTime().toString("yyyyMMdd hh:mm:ss");//当前时间
        }
    }
    else//中间
    {
        QString strNextTime = "";
        QString strPreviousTime = "";
        pNext = ui.listWidget->item(row+1);
        if (pNext)
        {
            CollisionListItem * pNextTask = (CollisionListItem *)ui.listWidget->itemWidget(pNext);
            strNextTime = pNextTask->GetTaskInfo().createTime;
            
        }
        pPrevious = ui.listWidget->item(row - 1);
        if (pPrevious)
        {
            CollisionListItem * pPreviousTask = (CollisionListItem *)ui.listWidget->itemWidget(pPrevious);
            strPreviousTime = pPreviousTask->GetTaskInfo().createTime;
        }
        if (strNextTime!=""&&strPreviousTime!="")
        {
            quint64 time = (QDateTime::fromString(strNextTime, "yyyyMMdd hh:mm:ss").toSecsSinceEpoch()+ QDateTime::fromString(strPreviousTime, "yyyyMMdd hh:mm:ss").toSecsSinceEpoch())/2;//取均值
            strCurrentTime = QDateTime::fromSecsSinceEpoch(time).toString("yyyyMMdd hh:mm:ss");
        }    
    }
    cuTask.createTime = strCurrentTime;
    pCurrentTask->SetTaskInfo(cuTask);
    QString strSql = QString("update CollisionTaskList set creatTime='%1' where taskName='%2'").arg(strCurrentTime).arg(cuTask.taskName);
    QString strMsg="";
    if (LocalDb::instance()->ExcuateSql(strSql, strMsg) != 0)
    {
        LOG_ERROR("update CollisionTaskList task: %s time  &s failed :%s", cuTask.taskName.toStdString().c_str(), strCurrentTime.toStdString().c_str(), strMsg.toStdString().c_str());
    }
    
}