抽象类类型的新表达式无效 [英] Invalid new expression of abstract class type

问题描述

我正在qt中构建一个文本编辑器，当我尝试实现一个简单的texthighlighter时我遇到了这个错误



这里是我的代码



myhighlighter.cpp

I am building a text editor in qt , i am having this error when i try to implemet a simple texthighlighter

here is my code

myhighlighter.cpp

#include "myhighlighter.h"
#include <QTextCharFormat>
#include <QDebug>

myhighlighter::myhighlighter(QWidget *parent) : QSyntaxHighlighter(parent)
{
    QDebug("myhighlighter initiated");
}

void myhighlighter::highlightblock(const QString &text)
{
    QTextCharFormat format;
    QRegExp rx(pattern);
    if(!rx.isValid() || rx.isEmpty() || rx.exactMatch("")){
        setFormat(0,text.length(),format);
    }
    format.setBackground(Qt::yellow);
    int index = rx.indexIn(text);
    while(index >= 0)
    {
        int length = rx.matchedLength();
        setFormat(index,length,format);
        index = rx.indexIn(text , length + index);
    }
}

myhighlihter.h

myhighlihter.h

#ifndef MYHIGHLIGHTER_H
#define MYHIGHLIGHTER_H
#include <QSyntaxHighlighter>
#include <QTextDocument>
#include <QString>

class myhighlighter : public QSyntaxHighlighter
{
    Q_OBJECT
public:
    explicit myhighlighter(QWidget *parent = 0);
virtual void highlightblock(const QString &text)=0;
    void setPattern(QString str){ pattern = str ; }
private:
    QString pattern;
};

#endif // MYHIGHLIGHTER_H

mainwindow.cpp的主要部分

main part in mainwindow.cpp

#include <QFile>
#include <QKeyEvent>
#include "myhighlighter.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QFont font;
    font.setFamily("monokai");
    font.setStyleHint(QFont::Monospace);
    font.setFixedPitch(true);
    font.setPointSize(10);
    ui->textEdit->setFont(font);
    ui->textEdit->acceptRichText();
    const int tabStop = 4;  // 4 characters
    QFontMetrics metrics(font);
    ui->textEdit->setTabStopWidth(tabStop * metrics.width(' '));
    this->setCentralWidget(ui->textEdit);
    highlighter = new myhighlighter(this);     // here i get the error
    highlighter->setDocument(ui->textEdit->document());
    // highlighter->setPattern(QString("class"));
    // highlighter->highlightblock(QString(""));
}

i得到错误，因为评论中显示的项目标题



请让我知道我错过了什么

i get an error as the title of the project in the line displayed in comment

please let me know what i am missing

推荐答案

我至少可以看到一个错误：帮助页面 QSyntaxHighlighter 表示它有一个功能

I can see at least one bug: the help page on QSyntaxHighlighter said that it has a function

virtual void highlightBlock(const QString & text) = 0;

这个函数通过本文档保持类抽象，因为它是纯虚拟，通常也称为抽象函数。这个类派生自 QObject 类，它是非抽象的（可以被认为是 pseudo-abstrac ），因此，具有一个具体的（非抽象）class（es），你必须创建一个派生自 QSyntaxHighlighter 的类，并最终覆盖 QSyntaxHighlighter :: highlightBlock 。



你还没有这样做。请注意你刚刚添加了这个功能：

This is the function which, by this document, keeps the class abstract, because it is pure virtual, which is also often called abstract function. This class is derived from QObject class which is non-abstract (can be considered pseudo-abstrac), so, to have a concrete (non-abstract) class(es), you have to create a class derived from QSyntaxHighlighter and eventually override QSyntaxHighlighter::highlightBlock.

You haven't done that. Note that you just added this function:

void highlightblock(const QString &text);

此函数无关虚拟空白 QSyntaxHighlighter :: highlightBlock ，它有不同的名称。 所以，你刚刚创建了一个全新的非虚拟功能，而不是覆盖一个必须被覆盖的功能。



（我希望你知道C ++是区分大小写的;可能你只是拼错了名字。）

-SA

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