每当我尝试在 QTextCursor 选择上调用 QTextCharFormat 时，父函数就会终止

Question

我最近运行遇到一个奇怪的问题，每当调用 QTextCursor::mergeCharFormat/setCharFormat/setBlockCharFormat 时，我的 QPlainTextEdit::selectionChanged 处理函数就会过早终止。此外，终止后它会再次调用并遇到相同的问题，从而导致无限循环。

我正在尝试复制许多文本编辑器（例如 Notepad++）中存在的功能，在该功能中选择一个词后，整个文档中的所有相似词都会突出显示。我的 TextEditor class 是从 QPlainTextEdit.

超载的

最小的可重现示例如下：

main.cpp:

#include "mainWindow.h"
#include <QtWidgets/QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    mainWindow w;
    w.show();
    return a.exec();
}

MainWindow.h:

#pragma once
#include <QtWidgets/QMainWindow>
#include "ui_mainWindow.h"
#include "TextEditor.h"

class mainWindow : public QMainWindow
{
    Q_OBJECT

public:
    mainWindow(QWidget *parent = Q_NULLPTR) : QMainWindow(parent)
    {
        ui.setupUi(this);

        auto textEdit = new TextEditor(this);
        textEdit->setPlainText("test lorem ipsum test\n dolor sit test");
        ui.tabWidget->addTab(textEdit, "Editor"); //Or any other way of adding the widget to the window
    }

private:
    Ui::mainWindowClass ui;
};

TextEditor.h:

正则表达式荧光笔部分基于this SO answer。

#pragma once
#include <QPlainTextEdit>

class TextEditor : public QPlainTextEdit
{
    Q_OBJECT

public:
    TextEditor(QWidget* parent) : QPlainTextEdit(parent)
    {
        connect(this, &QPlainTextEdit::selectionChanged, this, &TextEditor::selectChangeHandler);
    }

private:
    void selectChangeHandler()
    {
        //Ignore empty selections
        if (textCursor().selectionStart() >= textCursor().selectionEnd())
            return;

        //We only care about fully selected words (nonalphanumerical characters on either side of selection)
        auto plaintext = toPlainText();
        auto prevChar = plaintext.mid(textCursor().selectionStart() - 1, 1).toStdString()[0];
        auto nextChar = plaintext.mid(textCursor().selectionEnd(), 1).toStdString()[0];
        if (isalnum(prevChar) || isalnum(nextChar))
            return;

        auto qselection = textCursor().selectedText();
        auto selection = qselection.toStdString();

        //We also only care about selections that do not themselves contain nonalphanumerical characters
        if (std::find_if(selection.begin(), selection.end(), [](char c) { return !isalnum(c); }) != selection.end())
            return;

        //Prepare text format
        QTextCharFormat format;
        format.setBackground(Qt::green);

        //Find all words in our document that match the selected word and apply the background format to them
        size_t pos = 0;
        auto reg = QRegExp(qselection);
        auto cur = textCursor();
        auto index = reg.indexIn(plaintext, pos);
        while (index >= 0)
        {
            //Select matched text and apply format
            cur.setPosition(index);
            cur.movePosition(QTextCursor::EndOfWord, QTextCursor::KeepAnchor, 1);
            cur.mergeCharFormat(format); //This causes the selectChangeHandler function to terminate and then execute again, causing an infinite loop leading to a stack overflow

            //Move to next match
            pos = index + (size_t)reg.matchedLength();
            index = reg.indexIn(plaintext, pos);
        }
    }
};

我怀疑格式由于某种原因无法应用，可能导致在 Qt 中捕获并终止父函数的异常。我尝试在有问题的区域周围添加我自己的 try-catch 处理程序，但它什么也没做（如预期的那样）。

我不确定这是我的错还是 Qt 中的错误。有人知道我做错了什么或如何解决这个问题吗？

Answer 1

正在生成无限循环，因为获取文本更改似乎也会更改选择。一种可能的解决方案是使用 QSignalBlocker 来阻止信号：

void selectChangeHandler()
{
    const QSignalBlocker blocker(this); // <--- this line
    //Ignore empty selections
    if (textCursor().selectionStart() >= textCursor().selectionEnd())
        return;
    // ...

每当我尝试在 QTextCursor 选择上调用 QTextCharFormat 时，父函数就会终止

Parent function terminates whenever I try to call QTextCharFormat on QTextCursor selection

c++

qt

qplaintextedit

qtextcursor