#include "mainwindow.h"
#include "ui_mainwindow.h"
#include<QMenu>
#include<QMenuBar>
#include<QToolBar>
#include<QDockWidget>
#include<QTextEdit>
#include<QDialog>
#include<QAction>
#include<QMessageBox>
#include<QWindow>
#include <QFile>
#include <QFileDialog>
#include <QTextStream>
#include <QIcon>
#include<QString>
#include<QFont>
#include<QDebug>
#include<QFontDialog>
#include<QColorDialog>
#include<QPalette>
#include<QColor>
#include<QMessageBox>
#include<QImage>
#include<QTextDocumentFragment>
#include<QPicture>
#include<QFile>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
//背景
    edit->setParent(this);
    setCentralWidget(edit);
    QPalette pl = edit->palette();
    setWindowTitle("记事本鬼灭之刃版");
    this->resize(1000,800);
   setStyleSheet("border-image:url(:/a3.jpg)");

//菜单
    QMenuBar *bar=menuBar();
    setMenuBar(bar);
    bar->addSeparator();
    QMenu *m8=bar->addMenu("文件");
    QMenu *m1=bar->addMenu("工具");
    QMenu *m2=bar->addMenu("字号");
    QMenu *m3=bar->addMenu("颜色");
    QMenu *m9=bar->addMenu("字体");
    QMenu *m4=bar->addMenu("撤回");
    QMenu *m5=bar->addMenu("恢复");
    QMenu *m7=bar->addMenu("帮助");
//文件
    //新建
    QAction *file=new QAction(tr("新建"));
    file->setShortcut(tr("Ctrl+N"));
    m8->addAction(file);
    m8->addSeparator();
    connect(file,&QAction::triggered,this,&MainWindow::newfile);
    //打开
    QAction *open=new QAction(tr("打开"));
    open->setShortcut(tr("Ctrl+X"));
    m8->addAction(open);
    m8->addSeparator();
    connect(open,&QAction::triggered,this,&MainWindow::open);
    //关闭
    QAction *close=new QAction(tr("关闭"));
    close->setShortcut(tr("Ctrl+L"));
    m8->addAction(close);
    m8->addSeparator();
    connect(close,&QAction::triggered,this,&MainWindow::closefun);
//工具
    //复制
    QAction *copy=new QAction(tr("复制"));
    copy->setShortcut(tr("Ctrl+C"));
    m1->addAction(copy);
    m1->addSeparator();
    connect(copy,&QAction::triggered,this,&MainWindow::copyfun);
    //粘贴
    QAction *copywrite=new QAction(tr("粘贴"));
    copywrite->setShortcut(tr("Ctrl+V"));
    m1->addAction(copywrite);
    m1->addSeparator();
    connect(copywrite,&QAction::triggered,this,&MainWindow::copywritefun);
    //另存为
    QAction *down=new QAction(tr("另存为"));
    down->setShortcut(tr("Ctrl+A"));
    m1->addAction(down);
    m1->addSeparator();
    connect(down,&QAction::triggered,this,&MainWindow::downfun);
//字号
    //手写
    QAction *a1=new QAction("一号");
    m2->addAction(a1);
    m2->addSeparator();
    connect(a1,&QAction::triggered,[=](){
         edit->setStyleSheet("font-size : 12px");
    });
    QAction *a2=new QAction("二号",m2);
    m2->addAction(a2);
    m2->addSeparator();
    connect(a2,&QAction::triggered,[=](){
         edit->setStyleSheet("font-size : 14px");
    });
    QAction *a3=new QAction("三号",m2);
    m2->addAction(a3);
    m2->addSeparator();
    connect(a3,&QAction::triggered,[=](){
         edit->setStyleSheet("font-size : 16px");
    });
    QAction *a4=new QAction("四号",m2);
    m2->addAction(a4);
    m2->addSeparator();
    connect(a4,&QAction::triggered,[=](){
         edit->setStyleSheet("font-size : 18px");
    });
    QAction *a5=new QAction("五号",m2);
    m2->addAction(a5);
    m2->addSeparator();
    connect(a5,&QAction::triggered,[=](){
         edit->setStyleSheet("font-size : 20px");
    });
    QAction *a6=new QAction("六号",m2);
    m2->addAction(a6);
    m2->addSeparator();
    connect(a6,&QAction::triggered,[=](){
        edit->setStyleSheet("font-size : 22px");
    });
    QAction *a7=new QAction("七号",m2);
    m2->addAction(a7);
    m2->addSeparator();
    connect(a7,&QAction::triggered,[=](){
        edit->setStyleSheet("font-size : 24px");
    });
    QAction *a8=new QAction("八号",m2);
    m2->addAction(a8);
    m2->addSeparator();
    connect(a8,&QAction::triggered,[=](){
         edit->setStyleSheet("font-size : 26px");
    });
    //对话框
    QAction *a9=new QAction("更多选择");
    m2->addAction(a9);
    m2->addSeparator();
    connect(a9,&QAction::triggered,[=](){
        bool ok;
          QFont font = QFontDialog::getFont(&ok,this);
          if(ok)
              edit->setFont(font);
          else
              qDebug()<<tr("没有选择字体");
       } );
//颜色
    //手写— 红
    QAction *red=new QAction("红色");
    m3->addAction(red);
    m3->addSeparator();
    connect(red,&QAction::triggered,[=](){
        edit->setTextColor(QColor(255,0,0));
    });
    //手写- 绿
    QAction *green=new QAction("绿色");
    m3->addAction(green);
    m3->addSeparator();
    connect(green,&QAction::triggered,[=](){
        edit->setTextColor(QColor(0,255,0));
    });
    //手写- 蓝
    QAction *blue=new QAction("蓝色",m3);
    m3->addAction(blue);
    m3->addSeparator();
    connect(blue,&QAction::triggered,[=](){
        edit->setTextColor(QColor(0,0,255));
    });
    //对话框
    QAction *cmore=new  QAction("更多颜色");
    m3->addAction(cmore);
    connect(cmore,&QAction::triggered,[=](){
       QColor color = QColorDialog::getColor();
       if(color.isValid()){
           edit->setTextColor(color);
       }
    });
//字体
    //手写加粗斜体
    QAction *w1=new QAction("加粗");
    QAction *w2=new QAction("斜体");
    m9->addAction(w1);
    m9->addSeparator();
    m9->addAction(w2);
    m9->addSeparator();
    connect(w1,&QAction::triggered,[=]{
        edit->setStyleSheet("font-weight: bold;");
    });
    connect(w2,&QAction::triggered,[=]{
        edit->setFontItalic(true);
    });
    //更换字体
//撤回
    QAction *x1=new QAction("撤回");
    m4->addAction(x1);
    m4->addSeparator();
    x1->setShortcut(tr("Ctrl+Z"));
    connect(x1,&QAction::triggered,[=](){
         edit->undo();
    });
//恢复
    QAction *x2=new QAction("恢复");
    m5->addAction(x2);
    m5->addSeparator();
    x2->setShortcut(tr("Ctrl+M"));
    connect(x2,&QAction::triggered,[=](){
         edit->redo();
    });

//帮助
    QAction *hlep=new QAction("帮助");
    m7->addAction(hlep);
    hlep->setShortcut(tr("Ctrl+H"));
    connect(hlep,&QAction::triggered,[=](){
      QDialog dialog;
      dialog.setWindowTitle(tr("懒得写帮助，自己用用看吧"));
      dialog.exec();
    });
}

MainWindow::~MainWindow()
{
    delete ui;
}
void MainWindow::newfile(){
    edit->clear();
    edit->setText(QString());
}
void MainWindow::closefun(){
    QMessageBox box;
    box.setText("确定要关闭吗？");//用模态对话框来实现。
    box.setStandardButtons(QMessageBox::Yes|QMessageBox::No);
    if(box.exec()==QMessageBox::No){
        return;
    }
    else{
        this->close();
    }
}
void MainWindow::copyfun(){
    edit->copy();
}
void MainWindow::copywritefun(){
    edit->paste();
}
void MainWindow::downfun(){
    QString fn = QFileDialog::getSaveFileName(this,"另存为");
    QFile file(fn);
    file.open(QIODevice::Text|QIODevice::WriteOnly);//打开方式只写，并且是Text
    QTextStream in(&file);
    QString filecontent = edit->toPlainText();//toPlainText读取
    in << filecontent;
    file.close();
}
void MainWindow::open(){
    QString FileName=QFileDialog::getOpenFileName(this,"Open File",QDir::currentPath());
        QFile *file=new QFile;
        file->setFileName(FileName);
        bool ok=file->open(QIODevice::ReadOnly);    //判断是否只读模式打开
        if(ok){
            QTextStream in(file);   //类比c++的io流，使之与file绑定
            edit->setText(in.readAll());   //这个用法学c++的时候我还没看过
            file->close();//关闭文件和c++一样
            delete file;
        }
        else return;//打不开
}

头文件代码

Mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include<QTextEdit>
#include <QMouseEvent>
#include<QDockWidget>
#include <QPaintEvent>
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
private:
    Ui::MainWindow *ui;
    QString now;
    QTextEdit *edit=new QTextEdit;
public slots:
    void open();
    void copyfun();
    void copywritefun();
    void downfun();
    void newfile();
    void closefun();
};
#endif // MAINWINDOW_H