一起看代码来玩玩QT之08 Draw(first projiect 画板)

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本文介绍如何使用C++实现一个互动画板，用户可以通过点击和拖动鼠标绘制线条，并在画板上添加一个按钮。按钮的功能包括记录用户绘制的线条并在释放鼠标后保存最终形状。

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first: 一条线

MyWidget.h

#ifndef MYWIDGET_H
#define MYWIDGET_H

#include <QWidget>
#include "MyButton.h"

class MyWidget : public QWidget
{
    Q_OBJECT
public:
    explicit MyWidget(QWidget *parent = 0);

    MyButton* button;

    void paintEvent(QPaintEvent *);

    void mousePressEvent(QMouseEvent *);
    void mouseReleaseEvent(QMouseEvent *);
    void mouseMoveEvent(QMouseEvent *);

    QVector<QPoint>  _lines  //记录画过的东西

signals:

public slots:
    void slotButtonClicked();
};

#endif // MYWIDGET_H

MyWidget.cpp

#include "mywidgets.h"


#include<QApplication>
#include<QMouseEvent>
#include<QPainter>
MyWidgets::MyWidgets(QWidget *parent) : QWidget(parent)
{

}
void MyWidgets::paintEvent(QPaintEvent *) //调用：1 窗口初始化 2update 3 系统认为重绘时
{
    QPainter p(this);
    for(int i=0; i<_line.size()-1;i++)
    {
        p.drawLine(_line.at(i),_line.at(i++));
    }

}
void MyWidgets::mousePressEvent(QMouseEvent *ev)
{
    _line.append(ev->pos());
    
}

void MyWidgets::mouseMoveEvent(QMouseEvent *e)
{
    _line.append(e->pos());
    <pre name="code" class="cpp" style="color: rgb(255, 0, 0);">    update();

}void MyWidgets::mouseReleaseEvent(QMouseEvent *e){ _line.append(e->pos());}int main(int argc , char** argv){ QApplication app(argc, argv); MyWidgets w; w.show(); app.exec();}

second:画板

MyWidget.h

#ifndef MYWIDGET_H
#define MYWIDGET_H

#include <QWidget>
#include "MyButton.h"

class MyWidget : public QWidget
{
    Q_OBJECT
public:
    explicit MyWidget(QWidget *parent = 0);


    void paintEvent(QPaintEvent *);

    void mousePressEvent(QMouseEvent *);
    void mouseReleaseEvent(QMouseEvent *);
    void mouseMoveEvent(QMouseEvent *);

    QVector< QVector<QPoint> > _lines  //记录画过的东西

signals:

public slots:
    void slotButtonClicked();
};

#endif // MYWIDGET_H

MyWidget.cpp

#include "mywidgets.h"


#include<QApplication>
#include<QMouseEvent>
#include<QPainter>
MyWidgets::MyWidgets(QWidget *parent) : QWidget(parent)
{

}
void MyWidgets::paintEvent(QPaintEvent *) //调用：1 窗口初始化 2update 3 系统认为重绘时
{
    QPainter p(this);
    for(int i=0; i<_lines.size();i++)
    {
        QVector<QPoint> line = _lines.at(i);
        for(int j=0; j<line.size()-1;j++)
        {
            p.drawLine(line.at(j),line.at(j+1));
        }
    }



}
void MyWidgets::mousePressEvent(QMouseEvent *ev)
{
    QVector<QPoint> line;
    _lines.append(line);

    _lines.last().append(ev->pos());


}

void MyWidgets::mouseMoveEvent(QMouseEvent *e)
{
    _lines.last().append(e->pos());
     update();

}
void MyWidgets::mouseReleaseEvent(QMouseEvent *e)
{
    _lines.last().append(e->pos());

}

int main(int argc , char** argv)
{
    QApplication app(argc, argv);

    MyWidgets w;

    w.show();

    app.exec();
}

three 画一个button

MyButton.h

#ifndef MYBUTTON_H
#define MYBUTTON_H

#include <QWidget>

class MyButton : public QWidget
{
    Q_OBJECT
public:
    explicit MyButton(QWidget *parent = 0);
    MyButton(const QString& text, QWidget* parent = 0);

    QRect _rect;
    QString _text;
    bool _pressed;  //biaoji
    void mousePressEvent(QMouseEvent *);
    void mouseReleaseEvent(QMouseEvent *);

    void paintEvent(QPaintEvent *);

signals:
    void clicked();

public slots:

};

#endif // MYBUTTON_H

MyButton.cpp

#include "MyButton.h"
#include <QPainter>
#include <QMouseEvent>
MyButton::MyButton(QWidget *parent) :
    QWidget(parent), _rect(0, 0, 100, 30), _text(QString())
{
    _pressed = false;
    this->setGeometry(_rect);
}

MyButton::MyButton(const QString &text, QWidget *parent):
    QWidget(parent), _text(text), _rect(0, 0, 100, 30)
{
    _pressed = false;
    this->setGeometry(_rect);
}

void MyButton::mousePressEvent(QMouseEvent *)
{
    _pressed = true;
    update();
}

void MyButton::mouseReleaseEvent(QMouseEvent *ev)
{
    _pressed = false;
    update();

    if(_rect.contains(ev->pos()))  //鼠标在Button中才算 clicked
        emit clicked();   //发射一个信号
    // callback handler
}
void MyButton::paintEvent(QPaintEvent *)
{
    QPainter p(this);
    if(_pressed)
        p.setBrush(Qt::yellow);
    else
        p.setBrush(Qt::darkGray);
    p.drawRect(_rect);
    p.drawText(_rect, _text, QTextOption(Qt::AlignCenter));
}

MyWidget.h

#ifndef MYWIDGET_H
#define MYWIDGET_H

#include <QWidget>
#include "MyButton.h"

class MyWidget : public QWidget
{
    Q_OBJECT
public:
    explicit MyWidget(QWidget *parent = 0);

    MyButton* button;

    void paintEvent(QPaintEvent *);

    void mousePressEvent(QMouseEvent *);
    void mouseReleaseEvent(QMouseEvent *);
    void mouseMoveEvent(QMouseEvent *);

    QVector< QVector<QPoint> > _lines  //记录画过的东西

signals:

public slots:
    void slotButtonClicked();
};

#endif // MYWIDGET_H

MyWidget.cpp

#include "MyWidget.h"
#include <QPainter>
#include <QPixmap>
#include <QMouseEvent>
#include <QDebug>

MyWidget::MyWidget(QWidget *parent) :
    QWidget(parent)
{
    button = new MyButton("MyButton", this);
    connect(button, SIGNAL(clicked()), this, SLOT(slotButtonClicked()));

    button->setGeometry(30, 30, 100, 30);
}

void MyWidget::slotButtonClicked()
{
    qDebug() << "button is clicked";
}

void MyWidget::paintEvent(QPaintEvent *) ////调用：1 窗口初始化 2update 3 系统认为重绘时
{
    QPainter p(this);
    for(int i=0; i<_lines.size(); ++i)
    {
        const QVector<QPoint>& line = _lines.at(i);
        for(int j=0; j<line.size()-1; ++j)
        {
            p.drawLine(line.at(j), line.at(j+1));
        }
    }
}

void MyWidget::mouseMoveEvent(QMouseEvent *ev)
{
    if(_lines.size() == 0)
    {
        QVector<QPoint> line;
        _lines.append(line);
    }

    QVector<QPoint>& lastLine = _lines.last();
    lastLine.append(ev->pos());

    update();
}
void MyWidget::mousePressEvent(QMouseEvent *ev)
{
    QVector<QPoint> line;
    _lines.append(line);

    QVector<QPoint>& lastLine = _lines.last();
    lastLine.append(ev->pos());
}
void MyWidget::mouseReleaseEvent(QMouseEvent *ev)
{
    QVector<QPoint>& lastLine = _lines.last();
    lastLine.append(ev->pos());
}

#include <QApplication>
int main(int argc, char** argv)
{
    QApplication app(argc, argv);

    MyWidget w;
    w.show();

    return app.exec();
}