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connect(b4, &QPushButton::released, 
    []() mutable
    {
        qDebug()<<"1111";
    }
);
/*
    = :   把外部所有局部变量,类中所有成员以值传递，需要修改 加mutable关键字，比较安全
    this：类中所有成员，以值传递
    & ：  引用传递，外部的局部变量
*/

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//判断是谁发出的信号
QObject * mySender = sender();
//转换为按钮类型
QPushButton *p = (mySender)mySender;
if(NULL != p)
{
    p->text();
}

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/////foreach遍历QLinkedList<QString>
QLinkedList<QString> list;
...
QString str;
foreach (str, list)
    qDebug() << str;

/////QMap和QHash中
QMap<QString, int> map;
...
foreach (const QString &str, map.keys())
    qDebug() << str << ":" << map.value(str);

/////对于一个多值的（multi-valued）map
QMultiMap<QString, int> map;
...
foreach (const QString &str, map.uniqueKeys()) 
{
    foreach (int i, map.values(str))
        qDebug() << str << ":" << i;
}

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//QString -> QByteArray
QString str("hello");  
QByteArray bytes = str.toUtf8(); // QString转QByteArray方法1
bytes.toLocal8Bits();//本地编码 ANSI

//QByteArray -> char *
char *b = a.data();

//QString -> char*
str.toUtf8().data()

//char * -> QString
QString c = QString(p);

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#include <QDateTime>
    QDateTime curDataTime = QDateTime::currentDateTime();
    ui->lineEdit->setText(curDataTime.toString("yyyy-MM-dd hh:mm:ss:zzz A"));

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/////.h
private:
    QTimer *timer;

private slots:
    void on_timer_timeout();

/////.cpp
timer = new QTimer(this);

connect(timer, SIGNAL(timeout()), this, SLOT(on_timer_timeout()));
timer->start(1000);

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label->setText("");

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label->setPixmap(QPixmap("://image/xxxx.png"))
label->setScaledContents(true);

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#include <QMovie>
QMovie myMovie = new QMovie("://unage/xxx.gif");
label->setMovie(myMovie);
myMovie.start();
label->setScaledContents(true);

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label->setText("<h1><a href=\"https://www.baidu.com\">百度一下</a></h1>");
label->setOpenExternalLinks(true);

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selector{attribute: value}

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//鼠标事件
protected:
    void mousePressEvent(QMouseEvent *ev);
    void mouseReleaseEvent(QMouseEvent *ev);
    void mouseMoveEvent(QMouseEvent *ev);

    void leaveEvent(QEvent *event);
    void enterEvent(QEvent *event);

//键盘和定时器事件
protected:
    //键盘按下事件
    void keyPressEvent(QKeyEvent *event);
    //定时器事件
    void timerEvent(QTimerEvent *event);

/* Alt+Enter 生成代码 */

MyLabel::MyLabel(QWidget *parent) : QLabel(parent)
{
    //设置默认追踪鼠标
    this->setMouseTracking(true);
}

void MyLabel::mousePressEvent(QMouseEvent *ev)
{
    int a = ev->x();
    int b = ev->y();

    QString str = QString("<center><h1>press = (%1,%2)</h1></center>").arg(a).arg(b);
    this->setText(str);

    //判断是左键还是右键
    if(ev->button()==Qt::LeftButton)
    {
        qDebug()<<"左键按下";
    }

}

void MyLabel::mouseReleaseEvent(QMouseEvent *ev)
{
    int a = ev->x();
    int b = ev->y();

    QString str = QString("<center><h1>release = (%1,%2)</h1></center>").arg(a).arg(b);
    this->setText(str);


}

void MyLabel::mouseMoveEvent(QMouseEvent *ev)
{
    int a = ev->x();
    int b = ev->y();

    QString str = QString("<center><h1>move = (%1,%2)</h1></center>").arg(a).arg(b);
    this->setText(str);

}

void MyLabel::leaveEvent(QEvent *event)
{
    qDebug()<<"离开";
}

void MyLabel::enterEvent(QEvent *event)
{
    qDebug()<<"进入";
}

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

    //单位毫秒
    int timer_id = this->startTimer(1000);
    //停止定时器
//    this->killTimer(timer_id);
}

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

void MyWidget::keyPressEvent(QKeyEvent *event)
{
    qDebug()<<event->key();
    if(event->key() == Qt::Key_A)
    {
       qDebug()<<"keyA";
    }
}

void MyWidget::timerEvent(QTimerEvent *event)
{
    static int sec = 0;
    sec++;
    ui->label->setText(QString("%1").arg(sec));

//    if(event->timerId() == timer_id)
//    判断是哪个定时器
}

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virtual bool QObject::eventFilter(QObject *watched,QEvent* event)

//不想继续转发 返回true 否则false

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    //pixmap转image
    pixmap.load("../1.jpg");
    QImage tempImage = pixmap.toImage();
    //image转 QPiaxmap
    QPixmap tempPixmap = QPixmap::fromImage(tempImage);

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//构造函数
去窗口边框
setWindowFlags(Qt::FramelessWindowHint | windowFlags() );

//设置透明
setAttribute(Qt::WA_TranslucentBackground);


//重写paintEvent
设置背景图片

//重写鼠标按下和释放 用于移动窗口
求相对坐标

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void Widget::on_button_Read_clicked()
{
    QString path = QFileDialog::getOpenFileName(this,"open","../","TXT(*.txt)");

    if(path.isEmpty() == false)
    {
        QFile file(path);
        //打开 只读方式
        bool isOK = file.open(QIODevice::ReadOnly);
        if(isOK == true)
        {
            //读文件 显示到窗口 默认utf8
            QByteArray array = file.readAll();
            //显示到编辑区
            ui->textEdit->setText(array);
            file.close();
        }
    }
}

void Widget::on_button_Write_clicked()
{
    //选择保存路径
    QString path = QFileDialog::getSaveFileName(this,"save","../","txt(*.txt)");
    if(path.isEmpty() == false)
    {
        QFile file;//创建文件对象
        //关联文件名字
        file.setFileName(path);

        bool isok = file.open(QIODevice::WriteOnly);
        if(isok)
        {
            QString str = ui->textEdit->toPlainText();
            //QString -> QByteArray
            file.write(str.toUtf8());
            file.close();
        }

    }
}

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QFileInfo info(path);
info.fileName().toUtf8().data(); //显示utf8的

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tcpServer = new QTcpServer(this);

tcpServer->listen(QHostAddress::any,8888);

connect(tcpServer,&QTcpServer::newCOnnection,
    [=]()
    {
        tcpSocket = tcpServer->nextPendingCOnnection();
        QString ip=tcpSocket.peerAddress().toString();
        qint16 port=tcpSocket.peerPort();

        QString temp = QString("[%1:%2]:成功连接").arg(ip).arg(port);
    }
);

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/// .h
#include <QTimer>

private:
QTimer *myTimer;
/// .cpp
myTimer = new QTimer(this);
//定时器有个信号singal timeout()
connect(myTimer,&QTimer::timeout,
    [=]()
    {
        static int i = 0;
        i++;
        ui->lcdNumber->display(i);
    }
);

//startBUtton
if(myTimer->isActive() == false)
    myTimer->start(100);//启动定时器，时间间隔为100ms

//stop button
if(myTimer->isActive() == true)
    myTimer->stop();

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#include <QSqlDatabase>
#include <QMessageBox>
#include <QSqlError>
#include <QSqlQuery>

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

    //打印Qt支持的数据库驱动
    qDebug()<<QSqlDatabase::drivers();

    //添加Mysql数据库
    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");

    db.setHostName("127.0.0.1");
    db.setPort(10026);
    db.setUserName("root");
    db.setPassword("123");
    db.setDatabaseName("test"); //使用哪个数据库

    if(db.open() == false)
    {
        QMessageBox::warning(this,"错误","连接失败"+db.lastError().text());
    }
    else
    {
        QMessageBox::information(this,"提示","连接成功");

        //QSqlQuery q;
       // q.exec("select * from list;");

    }
}