自定义一个titlebar窗口，

不带任何资源、QSS，纯代码

1. 设置主窗口

透明背景，让central_widget透明方式显示，给后续main添加dropshadow效果，用于放置实际的业务控件。

setWindowFlags(Qt::FramelessWindowHint | Qt::WindowStaysOnTopHint);
setAttribute(Qt::WA_TranslucentBackground);QWidget *central_widget = new QWidget(this);
setCentralWidget(central_widget);
central_widget->setStyleSheet("background:transparent");QVBoxLayout *central_layout = new QVBoxLayout(central_widget);
central_layout->setMargin(5);  // 这个 margin 一般为effect的 一半QWidget *main = new QWidget(this);
central_layout->addWidget(main);QGraphicsDropShadowEffect *effect = new QGraphicsDropShadowEffect(this);effect->setBlurRadius(10);effect->setColor(QColor("#373737"));effect->setOffset(0,0);main->setStyleSheet("background-color: black");
main->setGraphicsEffect(effect);QVBoxLayout *vbox_main = new QVBoxLayout(main);
vbox_main->setMargin(0);
vbox_main->setSpacing(0);...
// 添加后续业务代码。

2. 自定义右侧的按钮组

QWidget *titlebar = new QWidget(this);
titlebar->setStyleSheet("background-color: rgb(192,192,192)");
titlebar->setMaximumHeight(28);
vbox_main->addWidget(titlebar);QHBoxLayout *titlebar_layout = new QHBoxLayout(titlebar);
titlebar_layout->setMargin(2);
titlebar_layout->setSpacing(2);titlebar_layout->addStretch();QPushButton* min_button = new QPushButton(this);
min_button->setIcon(style()->standardIcon(QStyle::SP_TitleBarMinButton));
titlebar_layout->addWidget(min_button);
connect(min_button, &QPushButton::pressed, this, [=]()
{showMinimized();
});QPushButton* max_button = new QPushButton(this);
max_button->setIcon(style()->standardIcon(QStyle::SP_TitleBarMaxButton));
titlebar_layout->addWidget(max_button);
connect(max_button, &QPushButton::pressed, this, [=]()
{showFullScreen();
});QPushButton* normal_button = new QPushButton(this);
normal_button->setIcon(style()->standardIcon(QStyle::SP_TitleBarNormalButton));
titlebar_layout->addWidget(normal_button);
connect(normal_button, &QPushButton::pressed, this, [=]()
{showNormal();
});
normal_button->setVisible(false);QPushButton* close_button = new QPushButton(this);
close_button->setIcon(style()->standardIcon(QStyle::SP_TitleBarCloseButton));
titlebar_layout->addWidget(close_button);
connect(close_button, &QPushButton::pressed, this, [=]()
{close();
});

其中，最小化、全屏化、正常化、关闭按钮，可以取 Qt内置的标准icon，

style()->standardIcon(QStyle::SP_TitleBarMinButton);
SP_TitleBarMaxButton
SP_TitleBarNormalButton
SP_TitleBarCloseButton

可通过QPainter来变色

QIcon changeColor(const QIcon &icon, const QSize &size, const QColor &color)
{QPixmap pixmap = new icon.pixmap(size);QPainter painter(&pixmap);painter.setCompositionMode(QPainter::CompositionMode_SourceIn);painter.fillRect(pixmap.rect(), color);return QIcon(pixmap);
}

通过获取topLevelWidget， 然后调用下列方法

    void showMinimized();void showMaximized();void showFullScreen();void showNormal();bool close();

3. 标题栏的拖动

void QFramelessShadowWindow::mousePressEvent(QMouseEvent *event)
{if (event->button() == Qt::LeftButton && event->x() < _max_button->x() - 30 && event->y() < 30){_dragging = true;_mouse_position = event->globalPos();_window_position = geometry().topLeft();}
}void QFramelessShadowWindow::mouseMoveEvent(QMouseEvent *event)
{if (_dragging && !_is_fullscreen){QPoint offset = event->globalPos() - _mouse_position;move( _window_position + offset);}
}void QFramelessShadowWindow::mouseReleaseEvent(QMouseEvent *event)
{if (event->button() == Qt::LeftButton)_dragging = false;
}

4. 最后一个问题

当全屏后，会出现 放置实际的业务控件的区域显示不全，此时不需要显示dropshadow的阴影效果。可以响应主窗口的changeEvent事件，动态对layout的margin进行调整

void QFramelessShadowWindow::changeEvent(QEvent *event)
{bool from_normal = false;if (QEvent::WindowStateChange == event->type()){QWindowStateChangeEvent *state_event = static_cast<QWindowStateChangeEvent *>(event);if (Q_NULLPTR != state_event){if (state_event->oldState() == Qt::WindowNoState){from_normal = true;}else if (state_event->oldState() == Qt::WindowFullScreen){_max_button->setVisible(true);_normal_button->setVisible(false);centralWidget()->layout()->setMargin(5);_is_fullscreen = false;}}}QMainWindow::changeEvent(event);Qt::WindowStates state = windowState();if (from_normal && state == Qt::WindowFullScreen){_max_button->setVisible(false);_normal_button->setVisible(true);centralWidget()->layout()->setMargin(0);_is_fullscreen = true;}
}