c++ - QPlainText 的子类不会扩展以填充布局

Question

我不明白为什么 Qt 网站上的 CodeEditor 示例没有按预期工作。每次我运行代码时，它都会像这样显示它，非常小并且不会扩展以占用所有可用空间。有谁知道为什么？我什至尝试设置固定大小、sizepolicy 和最小尺寸。不知道我在这里缺少什么。

主.cpp：

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

主窗口.cpp：

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QVBoxLayout>
#include <QLabel>
#include "codeeditor.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent)
{
    // controls
    auto *widget_main = new QWidget(this);
    auto *lay_main = new QVBoxLayout(widget_main);
    auto *label = new QLabel("Test");
    auto *editor = new CodeEditor();

    // layout
    lay_main->addWidget(label);
    lay_main->addWidget(editor);
    lay_main->setContentsMargins(5, 5, 5, 5);
}

MainWindow::~MainWindow()
{
}

代码编辑器.h：

#ifndef CODEEDITOR_H
#define CODEEDITOR_H

#include <QPlainTextEdit>
#include <QObject>

class QPaintEvent;
class QResizeEvent;
class QSize;
class QWidget;

class LineNumberArea;

// Main text editor
class CodeEditor : public QPlainTextEdit
{
    Q_OBJECT

    public:
        CodeEditor(QWidget *parent = 0);

        void lineNumberAreaPaintEvent(QPaintEvent *event);
        int lineNumberAreaWidth();

    protected:
        void resizeEvent(QResizeEvent *event) override;

    private slots:
        void updateLineNumberAreaWidth(int newBlockCount);
        void highlightCurrentLine();
        void updateLineNumberArea(const QRect &, int);

    private:
        QWidget *lineNumberArea;
};

// Line number gutter
class LineNumberArea : public QWidget
{
    public:
        LineNumberArea(CodeEditor *editor) : QWidget(editor) {
            codeEditor = editor;
        }

        QSize sizeHint() const override {
            return QSize(codeEditor->lineNumberAreaWidth(), 0);
        }

    protected:
        void paintEvent(QPaintEvent *event) override {
            codeEditor->lineNumberAreaPaintEvent(event);
        }

    private:
        CodeEditor *codeEditor;
};

#endif

代码编辑器.cpp：

#include "codeeditor.h"
#include <QtWidgets>
#include <QFontMetrics>


CodeEditor::CodeEditor(QWidget *parent) : QPlainTextEdit(parent)
{
    setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);

    lineNumberArea = new LineNumberArea(this);

    connect(this, SIGNAL(blockCountChanged(int)), this, SLOT(updateLineNumberAreaWidth(int)));
    connect(this, SIGNAL(updateRequest(QRect,int)), this, SLOT(updateLineNumberArea(QRect,int)));
    connect(this, SIGNAL(cursorPositionChanged()), this, SLOT(highlightCurrentLine()));

    updateLineNumberAreaWidth(0);
    highlightCurrentLine();
    setFixedSize(200, 200);
    setMinimumSize(200,200);
}


int CodeEditor::lineNumberAreaWidth()
{
    int digits = 1;
    int max = qMax(1, blockCount());
    while (max >= 10) {
        max /= 10;
        ++digits;
    }

    //int space = 3 + fontMetrics().horizontalAdvance(QLatin1Char('9')) * digits;
    int space = 3 + 12 * digits;

    return space;
}


void CodeEditor::updateLineNumberAreaWidth(int /* newBlockCount */)
{
    setViewportMargins(lineNumberAreaWidth(), 0, 0, 0);
}


void CodeEditor::updateLineNumberArea(const QRect &rect, int dy)
{
    if (dy)
        lineNumberArea->scroll(0, dy);
    else
        lineNumberArea->update(0, rect.y(), lineNumberArea->width(), rect.height());

    if (rect.contains(viewport()->rect()))
        updateLineNumberAreaWidth(0);
}


void CodeEditor::resizeEvent(QResizeEvent *e)
{
    QPlainTextEdit::resizeEvent(e);

    QRect cr = contentsRect();
    lineNumberArea->setGeometry(QRect(cr.left(), cr.top(), lineNumberAreaWidth(), cr.height()));
}


void CodeEditor::highlightCurrentLine()
{
    QList<QTextEdit::ExtraSelection> extraSelections;

    if (!isReadOnly()) {
        QTextEdit::ExtraSelection selection;

        QColor lineColor = QColor(Qt::yellow).lighter(160);

        selection.format.setBackground(lineColor);
        selection.format.setProperty(QTextFormat::FullWidthSelection, true);
        selection.cursor = textCursor();
        selection.cursor.clearSelection();
        extraSelections.append(selection);
    }

    setExtraSelections(extraSelections);
}


void CodeEditor::lineNumberAreaPaintEvent(QPaintEvent *event)
{
    QPainter painter(lineNumberArea);
    painter.fillRect(event->rect(), Qt::lightGray);


    QTextBlock block = firstVisibleBlock();
    int blockNumber = block.blockNumber();
    int top = (int) blockBoundingGeometry(block).translated(contentOffset()).top();
    int bottom = top + (int) blockBoundingRect(block).height();

    while (block.isValid() && top <= event->rect().bottom()) {
        if (block.isVisible() && bottom >= event->rect().top()) {
            QString number = QString::number(blockNumber + 1);
            painter.setPen(Qt::black);
            painter.drawText(0, top, lineNumberArea->width(), fontMetrics().height(),
                             Qt::AlignRight, number);
        }

        block = block.next();
        top = bottom;
        bottom = top + (int) blockBoundingRect(block).height();
        ++blockNumber;
    }
}

Answer 1

QMainWindow是一个特殊的小部件，因为它具有预设布局

因此，您必须通过以下方式设置主小部件setCentralWidget()：

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    auto *widget_main = new QWidget;
    auto *lay_main = new QVBoxLayout(widget_main);
    auto *label = new QLabel("Test");
    auto *editor = new CodeEditor();

    setCentralWidget(widget_main); // <-- +++

    // layout
    lay_main->addWidget(label);
    lay_main->addWidget(editor);
    lay_main->setContentsMargins(5, 5, 5, 5);
}

另一方面，如果您要使用布局，则不应为小部件设置固定大小，在您的情况下删除setFixedSize(200, 200)另一方面，建议您使用新语法进行连接：

CodeEditor::CodeEditor(QWidget *parent) : QPlainTextEdit(parent)
{
    setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);

    lineNumberArea = new LineNumberArea(this);

    connect(this, &QPlainTextEdit::blockCountChanged, this, &CodeEditor::updateLineNumberAreaWidth);
    connect(this, &QPlainTextEdit::updateRequest, this, &CodeEditor::updateLineNumberArea);
    connect(this, &QPlainTextEdit::cursorPositionChanged, this, &CodeEditor::highlightCurrentLine);

    updateLineNumberAreaWidth(0);
    highlightCurrentLine();
    // setFixedSize(200, 200); <-- ---
    setMinimumSize(200,200);
}