[Qt6.8.3] Why does QToolBar perform inconsistently on qt5 and qt6?

[victorman]

I am currently working on migrating my application from Qt5 to Qt6.

However, I found that the method I used to customize the MacOS title bar in Qt5 is no longer effective in Qt6.

I wrote a minimal demo to reproduce this problem.

This is the effect when using Qt5.15.12.

This is the effect when using Qt6.8.3

This is the mainwindow.mm.

#include "mainwindow.h"

#include <QPushButton>
#include <QToolBar>
#include <QHBoxLayout>
#include <QTimer>
#include <QMenuBar>
#include <QLabel>
#include <QApplication>
#include <AppKit/NSWindow.h>
#include <Cocoa/Cocoa.h>
#include <qdebug.h>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{

    setStyleSheet("MainWindow { background-color: red; }");
    setFixedSize(640, 640);
    
    QToolBar* toolBar = new QToolBar(this);
    toolBar->setFixedWidth(640);
    toolBar->setFixedHeight(30);
    toolBar->setStyleSheet("QToolBar {background-color: green;}");

    QWidget* titleBarWidget = new QWidget(this);
    titleBarWidget->setFixedWidth(640);
    titleBarWidget->setFixedHeight(30);
    titleBarWidget->setStyleSheet("QWidget {background-color: blue;}");
    

    QHBoxLayout* titleLayout = new QHBoxLayout(titleBarWidget);
    titleLayout->setContentsMargins(70, 0, 10, 0);

    QLabel* titleLabel = new QLabel("Custom Title Bar", titleBarWidget);
    titleLabel->setStyleSheet("QLabel { color: white; }");
    
    QPushButton* btn1 = new QPushButton("Click Me", titleBarWidget);
    btn1->setStyleSheet("QPushButton { background-color: white}");
    connect(btn1, &QPushButton::clicked, this, [this](bool){qDebug() << QString("Button clicked");});
    
    titleLayout->addWidget(titleLabel);
    titleLayout->addStretch();
    titleLayout->addWidget(btn1);
    titleBarWidget->setLayout(titleLayout);

    toolBar->layout()->addWidget(titleBarWidget);

    addToolBar(toolBar);
}

MainWindow::~MainWindow() {}

void MainWindow::showEvent(QShowEvent *event) {
    QMainWindow::showEvent(event);
    qDebug() << "Qt Version:" << QT_VERSION_MAJOR << "." << QT_VERSION_MINOR << "." << QT_VERSION_PATCH;
#ifdef Q_OS_MACOS
    QTimer::singleShot(0, this, [this]() {
        NSView* view = (__bridge NSView*)this->winId();
        NSWindow* nsWindow = view.window;
        
        if (nsWindow) {
            nsWindow.titleVisibility = NSWindowTitleHidden;
            nsWindow.titlebarAppearsTransparent = YES;
            nsWindow.styleMask |= NSWindowStyleMaskFullSizeContentView;
        }
    });
#endif
}

Or do I have to implement these three buttons by myself?

[victorman]

I found that in QT version 6.8.3, when using the styleMask of NSWindow, only MainWindow itself would extend to the title bar, while CentralWidget and ToolBar would not extend to the title bar.