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Qt QML创建多线程（示例存读数据库）

news 2025/10/2 10:09:23

最近做了个小项目，发现当数据库中数据量过大时，GUI界面就会卡死，因为耗时的读取操作会阻塞主线程。为了解决这个问题，我就使用了多线程来稍微重构了一下，用子线程来处理这类耗时任务，而让主线程负责绘制界面，从而保持界面响应。

那么如何创建一个子线程来与主线程进行数据交互呢，下面我来码个例子：

一、创建类

创建继承QObject的主线程类和子线程类，并声明槽函数和信号

//MainThread.h#ifndef MAINTHREAD_H
#define MAINTHREAD_H#include <QObject>
#include "multithread.h"
#include <QThread>class MainThread : public QObject
{Q_OBJECT
public:explicit MainThread(QObject *parent = nullptr);~MainThread();    //析构函数，当程序退出时自动调用private slots:void getdata();    //释放dataready信号void loaddata(const QVariantList &data);    //释放dataload信号signals:void to_getdata(const QVariantList &data);    //通知子线程去准备数据void to_loaddata();    //通知子线程去加载数据void dataready();    //子线程数据准备完毕void dataload(const QVariantList &data);    //子线程数据加载完毕private:MultiThread *worker;    //工作类对象QThread *workthread;    //子线程对象
};#endif // MAINTHREAD_H

//MultiThread.h#ifndef MULTITHREAD_H
#define MULTITHREAD_H#include <QObject>
#include <QSqlDatabase>class MultiThread : public QObject
{Q_OBJECT
public:explicit MultiThread(QObject *parent = nullptr);~MultiThread();public slots:void do_getdata(const QVariantList &data);    //处理保存数据void do_loaddata();    //处理读取数据signals:void dataready(const QVariantList &data);    //数据保存结束void datachange();    //数据读取结束private:void init();    //初始化创建QSqlDatabase db;
};#endif // MULTITHREAD_H

二、实现子线程槽函数

我们先实现子线程中实际处理数据的槽函数，例子中就是实现了一下数据库的存读操作，并在操作结束后发出信号来通知主线程

//MultiThread.cpp#include "multithread.h"
#include <QSqlQuery>
#include <QSqlDatabase>
#include <QSqlError>MultiThread::MultiThread(QObject *parent): QObject{parent}
{init();
}MultiThread::~MultiThread()
{if(db.open()){db.close();}
}void MultiThread::do_getdata(const QVariantList &data)
{QSqlQuery cleardata(db);cleardata.exec("DELETE FROM sample");QSqlQuery insertdata(db);insertdata.prepare("INSERT INTO sample (number,name,major)""VALUES (?,?,?)");for(const QVariant &piece:data){QVariantMap map;map=piece.toMap();insertdata.addBindValue(map["number"]);insertdata.addBindValue(map["name"]);insertdata.addBindValue(map["major"]);if(!insertdata.exec()){qWarning()<<"子线程添加数据失败"<<insertdata.lastError().text();}}emit datachange();    //发出保存数据操作结束的信号qDebug()<<"子线程保存成功";
}void MultiThread::do_loaddata()
{QVariantList list;QSqlQuery query(db);query.exec("SELECT * FROM sample");while(query.next()){QVariantMap map;map["number"]=query.value(0).toInt();map["name"]=query.value(1).toString();map["major"]=query.value(2).toString();list.append(map);}qDebug()<<"子线程读取成功";emit dataready(list);    //发出读取数据操作结束的信号
}void MultiThread::init()
{if(QSqlDatabase::contains("example")){db=QSqlDatabase::database("example");}else{db=QSqlDatabase::addDatabase("QSQLITE","example");}db.setDatabaseName("sample.db");if(!db.open()){qDebug()<<"子线程打开数据库失败"<<db.lastError().text();}QSqlQuery query(db);query.prepare("CREATE TABLE IF NOT EXISTS sample(""number INTEGER PRIMARY KEY,""name TEXT,""major TEXT"")");if(!query.exec()){qWarning()<<"子线程创建数据库失败"<<query.lastError().text();}
}

三、在主线程类中实现信号与槽的连接

用信号与槽机制实现主线程和子线程的交互，并发出信号通知GUI界面更新操作

//MainThread.cpp#include "mainthread.h"
#include <QThread>MainThread::MainThread(QObject *parent): QObject{parent}
{workthread=new QThread(this);    //创建子线程，当主线程销毁时worker=new MultiThread();    //创建工作类的实例worker->moveToThread(workthread);    //将其移动至子线程//线程管理，防止内存泄漏connect(workthread,&QThread::finished,worker,&QObject::deleteLater);    //当子线程结束时，调用worker->deleteLater()，即自动销毁工作类对象connect(workthread,&QThread::finished,workthread,&QObject::deleteLater);    //同上，当子线程结束时，销毁子线程本身//存读操作connect(this,&MainThread::to_getdata,worker,&MultiThread::do_getdata);    //存储操作//当MainThread对象发出to_getdata信号时，worker会在子线程接收并调用do_getdata槽函数connect(worker,&MultiThread::datachange,this,&MainThread::getdata);    //当woker完成do_getdata后发出datachange信号，MainThread对象调用getdata槽函数发出dataready信号，通知GUI界面加载数据connect(this,&MainThread::to_loaddata,worker,&MultiThread::do_loaddata);    //读取操作connect(worker,&MultiThread::dataready,this,&MainThread::loaddata);workthread->start();    //启动子线程
}MainThread::~MainThread()
{workthread->quit();    //发出退出请求workthread->wait();    //阻塞调用线程，确保子线程退出
}void MainThread::getdata()
{emit dataready();
}void MainThread::loaddata(const QVariantList &data)
{emit dataload(data);
}

四、QML示例

我在main.qml中写了个ListView来演示了一下存读操作

//main.qmlimport QtQuick
import QtQuick.Controls.Material
import mainthread 1.0Window {width: 640height: 480visible: truetitle: qsTr("Hello World")//ListModel先填写数据，保存后注释掉，再次打开验证读取ListModel{id:examplemodel// ListElement{//     number:12//     name:"小明"//     major:"计算机"// }// ListElement{//     number:16//     name:"小李"//     major:"土木工程"// }}ListView{anchors.centerIn: parentwidth: 290height: 480model:examplemodelclip:truespacing:40delegate: Rectangle{width: 290height: 30Row{spacing: 50Text {text:model.numberanchors.verticalCenter: parent.verticalCenterfont.pixelSize: 20}Text {text:model.nameanchors.verticalCenter: parent.verticalCenterfont.pixelSize: 20}Text {text:model.majoranchors.verticalCenter: parent.verticalCenterfont.pixelSize: 20}}}Component.onCompleted: {maintd.to_loaddata()    //组件加载完毕时发出to_loaddata信号，请求子线程加载}}Button{anchors.right: parent.rightanchors.top: parent.topheight: 60width: 100text: "保存"onClicked: {let data=[]for(let i=0;i<examplemodel.count;i++){let getdata=examplemodel.get(i)data.push({number:getdata.number,name:getdata.name,major:getdata.major})}maintd.to_getdata(data)    //点击保存发出to_getdata信号，请求子线程保存}}MainThread{id:maintdonDataready:{    //信号处理器，当MainThread发出dataready信号时，打印“保存成功”console.log("保存成功")}onDataload: (data)=>{    //当MainThread发出dataload信号时，捕获data，更新examplemodelexamplemodel.clear()for(let i=0;i<data.length;i++){examplemodel.append(data[i])}}}
}

简单来说，整体逻辑其实就是，在QML中发出信号，请求子线程处理任务，子线程完成操作后发出信号通知主线程，主线程调用槽函数接收数据并再次发出信号通知QML，QML通过信号处理器捕获信号并响应。

通过使用多线程，便能够实现先弹出加载动画，等到数据加载完毕后再显示等效果，从而提升界面流畅度。同时，多个线程也能够并行执行多个任务，有效的提高处理性能

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