一、作业

        1：实现绘图的时候，颜色的随时调整；

        2：追加橡皮擦功能；

        3：配合键盘事件，实现功能；

        当键盘按 ctrl+z 的时候，撤销最后一次绘图。

【Headers / widget.h】：

#ifndef WIDGET_H
#define WIDGET_H#include <QWidget>
#include <QPaintEvent>
#include <QPainter>
#include <QDebug>
#include <QMouseEvent>
#include <QLine>
#include <QVector>
#include <QColorDialog>
#include <QColor>
#include <QKeyEvent>QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACEclass Widget : public QWidget
{Q_OBJECTpublic:Widget(QWidget *parent = nullptr);~Widget();private:Ui::Widget *ui;QPainter painter;QPen pen;QPoint start;QPoint end;QVector<QLine> lines;QColor color;QColor previousColor; //橡皮擦模式前的颜色QVector<QColor> colors;int width = 1;QVector<int> widths;bool isEraserMode = false; //橡皮擦模式标志protected:virtual void paintEvent(QPaintEvent *event) override;virtual void mouseMoveEvent(QMouseEvent *event) override;virtual void mousePressEvent(QMouseEvent *event) override;virtual void mouseReleaseEvent(QMouseEvent *event) override;virtual void keyPressEvent(QKeyEvent *event) override;private slots:void on_pushButton_clicked();void on_pushButton_2_clicked();void on_pushButton_3_clicked();void on_pushButton_4_clicked();void on_pushButton_5_clicked();
};
#endif // WIDGET_H

【Sources / widget.cpp】：

#include "widget.h"
#include "ui_widget.h"Widget::Widget(QWidget *parent): QWidget(parent), ui(new Ui::Widget)
{ui->setupUi(this);
}Widget::~Widget()
{delete ui;
}void Widget::paintEvent(QPaintEvent *event)
{painter.begin(this);painter.setPen(pen);// 遍历所有线段，并为每条线段设置对应的颜色for(int i = 0; i < lines.size(); ++i){// 使用存储的颜色pen.setColor(colors.at(i));pen.setWidth(widths.at(i));painter.setPen(pen);painter.drawLine(lines.at(i));}painter.end();
}void Widget::mouseMoveEvent(QMouseEvent *event)
{end = event->pos();QLine line(start, end);// 将鼠标绘制的每一根线段存入QVector中，即lines里面lines << line;colors << color;widths << width;// 更新坐标start = end;// 手动触发paintEvent绘图事件update();
}void Widget::mousePressEvent(QMouseEvent *event)
{start = event->pos();
}void Widget::mouseReleaseEvent(QMouseEvent *event)
{end = event->pos();
}void Widget::keyPressEvent(QKeyEvent *event)
{qDebug() << "Warning: 主子，这家伙按下了 Ctrl+Z 呀！！！";if(event->modifiers() == Qt::ControlModifier && event->key() == Qt::Key_Z){if(!lines.isEmpty()){lines.removeLast();colors.removeLast();widths.removeLast();update();}}
}// 打开调色板
void Widget::on_pushButton_clicked()
{color = QColorDialog::getColor(Qt::black, this, "选择颜色");
}// 画笔宽度
void Widget::on_pushButton_2_clicked()
{width = 1;
}void Widget::on_pushButton_3_clicked()
{width = 5;
}void Widget::on_pushButton_4_clicked()
{width = 10;
}
// 橡皮擦
void Widget::on_pushButton_5_clicked()
{// 切换橡皮擦模式isEraserMode = !isEraserMode;if(isEraserMode){// 进入橡皮擦模式，保存当前颜色并将画笔颜色设置为窗口背景色previousColor = color;// 橡皮擦设置为背景色color = palette().color(QPalette::Window);// 按钮文字状态改为“切换到画笔”ui->pushButton_5->setText("切换到画笔");}else{// 退出橡皮擦模式，恢复画笔颜色为之前保存的颜色color = previousColor;// 按钮文字状态改为“橡皮擦”ui->pushButton_5->setText("橡皮擦");}
}

【Sources / main.cpp】：

#include "widget.h"#include <QApplication>int main(int argc, char *argv[])
{QApplication a(argc, argv);Widget w;w.show();return a.exec();
}

【测试结果UI】：