参考：https://www.cnblogs.com/xufeiyang/p/3313104.html
这个类是关于无边框窗体的拖动和改变大小的。如果是QWidget，请将继承类改为QWidget，并将源文件的QDialog用QWidget替换。
我曾想将这个类作为中间类，让窗口类继承此类，这样如果有多个无边框窗口，就不用每个窗口都作重复改变了，但是没有成功。由于时间关系，没再做深入研究。以后有时间再说吧。
头文件：
1 #ifndef CustomFrameLessWidget_H
2 #define CustomFrameLessWidget_H
3
4 #include <QRect>
5 #include <QDialog>
6 #include <QWidget>
7 #include <QMouseEvent>
8
9 #define PADDING 2
10 enum Direction { UP=0, DOWN=1, LEFT, RIGHT, LEFTTOP, LEFTBOTTOM, RIGHTBOTTOM, RIGHTTOP, NONE };
11
12 class CustomFrameLessWidget : public QDialog
13 {
14 Q_OBJECT
15 public:
16 CustomFrameLessWidget(QWidget* parent = NULL);
17 void region(const QPoint &cursorGlobalPoint);
18 protected:
19 void mouseReleaseEvent(QMouseEvent *event);
20 void mouseMoveEvent(QMouseEvent *event);
21 void mousePressEvent(QMouseEvent *event);
22 public:
23 bool isLeftPressDown; // 判断左键是否按下
24 QPoint dragPosition; // 窗口移动拖动时需要记住的点
25 Direction dir; // 窗口大小改变时，记录改变方向
26
27 };
28
29 #endif // CustomFrameLessWidget_H
源文件：
1 #include "CustomFrameLessWidget.h"
2
3 CustomFrameLessWidget::CustomFrameLessWidget(QWidget* parent):QDialog(parent)
4 {
5 isLeftPressDown = false;
6 this->dir = NONE;
7 this->setMinimumHeight(100);
8 this->setMinimumWidth(150);
9 this->setWindowFlags(Qt::FramelessWindowHint|Qt::WindowSystemMenuHint); // 设置成无边框对话框
10 this->setMouseTracking(true);// 追踪鼠标
11 // this->setStyleSheet("QDialog{background:url(:/bg_main.png)}"); // 设置样式背景色，可有可无
12 }
13
14 void CustomFrameLessWidget::region(const QPoint &cursorGlobalPoint)
15 {
16 // 获取窗体在屏幕上的位置区域，tl为topleft点，rb为rightbottom点
17 QRect rect = this->rect();
18 QPoint tl = mapToGlobal(rect.topLeft());
19 QPoint rb = mapToGlobal(rect.bottomRight());
20
21 int x = cursorGlobalPoint.x();
22 int y = cursorGlobalPoint.y();
23
24 if(tl.x() + PADDING >= x && tl.x() <= x && tl.y() + PADDING >= y && tl.y() <= y) {
25 // 左上角
26 dir = LEFTTOP;
27 this->setCursor(QCursor(Qt::SizeFDiagCursor)); // 设置鼠标形状
28 } else if(x >= rb.x() - PADDING && x <= rb.x() && y >= rb.y() - PADDING && y <= rb.y()) {
29 // 右下角
30 dir = RIGHTBOTTOM;
31 this->setCursor(QCursor(Qt::SizeFDiagCursor));
32 } else if(x <= tl.x() + PADDING && x >= tl.x() && y >= rb.y() - PADDING && y <= rb.y()) {
33 //左下角
34 dir = LEFTBOTTOM;
35 this->setCursor(QCursor(Qt::SizeBDiagCursor));
36 } else if(x <= rb.x() && x >= rb.x() - PADDING && y >= tl.y() && y <= tl.y() + PADDING) {
37 // 右上角
38 dir = RIGHTTOP;
39 this->setCursor(QCursor(Qt::SizeBDiagCursor));
40 } else if(x <= tl.x() + PADDING && x >= tl.x()) {
41 // 左边
42 dir = LEFT;
43 this->setCursor(QCursor(Qt::SizeHorCursor));
44 } else if( x <= rb.x() && x >= rb.x() - PADDING) {
45 // 右边
46 dir = RIGHT;
47 this->setCursor(QCursor(Qt::SizeHorCursor));
48 }else if(y >= tl.y() && y <= tl.y() + PADDING){
49 // 上边
50 dir = UP;
51 this->setCursor(QCursor(Qt::SizeVerCursor));
52 } else if(y <= rb.y() && y >= rb.y() - PADDING) {
53 // 下边
54 dir = DOWN;
55 this->setCursor(QCursor(Qt::SizeVerCursor));
56 }else {
57 // 默认
58 dir = NONE;
59 this->setCursor(QCursor(Qt::ArrowCursor));
60 }
61 }
62
63 void CustomFrameLessWidget::mouseReleaseEvent(QMouseEvent *event)
64 {
65 if(event->button() == Qt::LeftButton) {
66 isLeftPressDown = false;
67 if(dir != NONE) {
68 this->releaseMouse();
69 this->setCursor(QCursor(Qt::ArrowCursor));
70 }
71 }
72 }
73
74 void CustomFrameLessWidget::mousePressEvent(QMouseEvent *event)
75 {
76 switch(event->button()) {
77 case Qt::LeftButton:
78 isLeftPressDown = true;
79 if(dir != NONE) {
80 this->mouseGrabber();
81 } else {
82 dragPosition = event->globalPos() - this->frameGeometry().topLeft();
83 }
84 break;
85 case Qt::RightButton:
86 this->close();
87 break;
88 default:
89 QDialog::mousePressEvent(event);
90 }
91
92 }
93
94 void CustomFrameLessWidget::mouseMoveEvent(QMouseEvent *event)
95 {
96 QPoint gloPoint = event->globalPos();
97 QRect rect = this->rect();
98 QPoint tl = mapToGlobal(rect.topLeft());
99 QPoint rb = mapToGlobal(rect.bottomRight());
100
101 if(!isLeftPressDown) {
102 this->region(gloPoint);
103 } else {
104
105 if(dir != NONE) {
106 QRect rMove(tl, rb);
107
108 switch(dir) {
109 case LEFT:
110 if(rb.x() - gloPoint.x() <= this->minimumWidth())
111 rMove.setX(tl.x());
112 else
113 rMove.setX(gloPoint.x());
114 break;
115 case RIGHT:
116 rMove.setWidth(gloPoint.x() - tl.x());
117 break;
118 case UP:
119 if(rb.y() - gloPoint.y() <= this->minimumHeight())
120 rMove.setY(tl.y());
121 else
122 rMove.setY(gloPoint.y());
123 break;
124 case DOWN:
125 rMove.setHeight(gloPoint.y() - tl.y());
126 break;
127 case LEFTTOP:
128 if(rb.x() - gloPoint.x() <= this->minimumWidth())
129 rMove.setX(tl.x());
130 else
131 rMove.setX(gloPoint.x());
132 if(rb.y() - gloPoint.y() <= this->minimumHeight())
133 rMove.setY(tl.y());
134 else
135 rMove.setY(gloPoint.y());
136 break;
137 case RIGHTTOP:
138 rMove.setWidth(gloPoint.x() - tl.x());
139 rMove.setY(gloPoint.y());
140 break;
141 case LEFTBOTTOM:
142 rMove.setX(gloPoint.x());
143 rMove.setHeight(gloPoint.y() - tl.y());
144 break;
145 case RIGHTBOTTOM:
146 rMove.setWidth(gloPoint.x() - tl.x());
147 rMove.setHeight(gloPoint.y() - tl.y());
148 break;
149 default:
150 break;
151 }
152 this->setGeometry(rMove);
153 } else {
154 move(event->globalPos() - dragPosition);
155 event->accept();
156 }
157 }
158 QDialog::mouseMoveEvent(event);
159 }