setWindowFlags(Qt::FramelessWindowHint); /* 注意：如果單純開啟窗口透明層效果，在Windows系統(tǒng)中必須設(shè)置, 其他系統(tǒng)可忽略。 */
setAttribute(Qt::WA_TranslucentBackground);

void paintEvent(QPaintEvent *)
{
  QPainter painter(this);
  /* 0x20為透明層顏色，可自定義設(shè)置為0x0到0xff */
  painter.fillRect(this->rect(), QColor(0, 0, 0, 0x20)); 
}

void mousePressEvent(QMouseEvent *event)
{
  if (event->button() == Qt::LeftButton) {
    /* 捕獲按下時坐標 */
    m_startPoint = frameGeometry().topLeft() - event->globalPos();
  }
}

void mouseMoveEvent(QMouseEvent *event)
{
  /* 移動窗口 */
  this->move(event->globalPos() + m_startPoint);
}

#include <QWidget>
#include <QVBoxLayout>
#include <QPushButton>
#include <QPainter>
#include <QMouseEvent>

class TransparentWidget : public QWidget
{
  Q_OBJECT
public:
  TransparentWidget(QWidget *parent = 0)
    : QWidget(parent)
  {
    setWindowTitle(QString::fromLocal8Bit("透明無邊框窗口"));
    setFixedSize(480, 320);
    setWindowFlags(Qt::FramelessWindowHint);
    setAttribute(Qt::WA_TranslucentBackground);

    QPushButton *button = new QPushButton("Hello world!", this);
    button->setGeometry(5, 5, 80, 40);
  }

  void paintEvent(QPaintEvent *)
  {
    QPainter painter(this);
    painter.fillRect(this->rect(), QColor(0, 0, 0, 0x20)); /* 設(shè)置透明顏色 */
  }

  void mousePressEvent(QMouseEvent *event)
  {
    if (event->button() == Qt::LeftButton) {
      m_startPoint = frameGeometry().topLeft() - event->globalPos();
    }
  }

  void mouseMoveEvent(QMouseEvent *event)
  {
    this->move(event->globalPos() + m_startPoint);
  }

private:
  QPoint m_startPoint;
};