拖拽之路（三）：自定义QListView实现美观的拖拽样式（拖拽即选中）
| 环境配置 ：MinGW + QT 5.12 |
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这种自定义拖拽样式的灵感来自于Chrome浏览器的书签栏。本文中拖拽的特点是：拖拽即选中。
实现功能及方法：
- 拖拽功能实现：继承QListView（重写drag事件）
- item在release时被选中：继承QListView （重写mousePressEvent和mouseReleaseEvent）
- item在被hover时改变图标样式：继承QStandardItem + 继承QStyledItemDelegate
- 绘制dropIndicator：继承QListView（使用update()进行控制） + 继承QStyledItemDelegate （使用画笔进行绘制）
拖拽时缩略图thumbnail类：
- Qt绘制形状不规则窗口（一）
推荐其它关于拖拽的文章：
- 拖拽之路（原生之初一）：自定义QListWidget实现美观的拖拽样式
- 拖拽之路（原生之初二）：自定义QListView实现美观的拖拽样式
- 拖拽之路（一）：自定义QListWidget实现美观的拖拽样式（拖拽即选中）
- 拖拽之路（二）：自定义QListWidget实现美观的拖拽样式（拖拽不影响选中）
- 拖拽之路（三）：自定义QListView实现美观的拖拽样式（拖拽即选中）
- 拖拽之路（四）：自定义QListView实现美观的拖拽样式（拖拽不影响选中）
- 拖拽之路（五）：自定义QListWidget实现美观的拖拽样式（拖拽不影响选中 + doAutoScroll）
这里需要说明一下：QListView是鼠标press时item就会被选中，自定义的TestListView类重写了mousePressEvent和mouseReleaseEvent使得item在鼠标release时才会被选中。至于为什么这样做，是因为Chrome浏览器的书签栏以及网易云音乐的选项列表都是在鼠标release时才会触发选中…
正是由于item在鼠标release时才会被选中，所以才会出现 拖拽即选中 和 拖拽不影响选中 两种情况，而QListView是鼠标press时item就会被选中，所以只能是 拖拽即选中（拖拽的条件是press，导致item在触发拖拽时就被选中）。
（1）TestListViewItem类继承自QStandardItem
- TestListViewItem.h文件：
class TestListViewItem : public QStandardItem
{
public:
explicit TestListViewItem();
explicit TestListViewItem(const QIcon &icon, const QIcon &icon_hover, const QString &text);
QIcon Img;
QIcon Img_hover;
};
- TestListViewItem.c文件：
TestListViewItem::TestListViewItem()
:QStandardItem()
{
}
TestListViewItem::TestListViewItem(const QIcon &icon, const QIcon &icon_hover, const QString &text)
:QStandardItem()
{
Img = icon;
Img_hover = icon_hover;
setIcon(Img);
setText(text);
}
（2）TestListView类继承自QListView
- TestListView.h文件：
class TestListView : public QListView
{
Q_OBJECT
public:
explicit TestListView(QWidget *parent = nullptr);
bool isDraging() const {
return IsDraging;}
int offset() const {
return 19;}
int highlightedRow() const {
return theHighlightedRow;}
int dragRow() const {
return theDragRow;}
static QString myMimeType() {
return QStringLiteral("TestListView/text-icon-icon_hover"); }
protected:
void mousePressEvent(QMouseEvent *event) override;
void mouseReleaseEvent(QMouseEvent *event) override;
void mouseMoveEvent(QMouseEvent *event) override;
void dragEnterEvent(QDragEnterEvent *event) override;
void dragLeaveEvent(QDragLeaveEvent *event) override;
void dragMoveEvent(QDragMoveEvent *event) override;
void dropEvent(QDropEvent *event) override;
private:
QPoint startPos;
bool IsDraging = false;
int theHighlightedRow = -2;
int oldHighlightedRow = -2;
int theDragRow = -1;
int theInsertRow = -1;
};
- TestListView.c文件：
TestListView::TestListView(QWidget *parent) :
QListView(parent)
{
// setMouseTracking(true);
// setDragEnabled(true);
setAcceptDrops(true);
// setDropIndicatorShown(false);
// setDefaultDropAction(Qt::MoveAction);
}
//记录拖拽初始位置
void TestListView::mousePressEvent(QMouseEvent *event)
{
if(event->buttons() & Qt::LeftButton){
startPos = event->pos();
}
}
void TestListView::mouseReleaseEvent(QMouseEvent *event)
{
if((event->pos() - startPos).manhattanLength() > 5) return;
QModelIndex index = indexAt(event->pos());
setCurrentIndex(index); //鼠标relesse时才选中
}
void TestListView::mouseMoveEvent(QMouseEvent *event)
{
if(event->buttons() & Qt::LeftButton){
if((event->pos() - startPos).manhattanLength() < QApplication::startDragDistance()) return;
QModelIndex theDragIndex = indexAt(startPos);
theDragRow = theDragIndex.row();
setCurrentIndex(theDragIndex); //拖拽即选中
QStandardItemModel *listModel = qobject_cast<QStandardItemModel *>(model());
TestListViewItem *theDragItem = static_cast<TestListViewItem *>(listModel->item(theDragRow));
//[1]把拖拽数据放在QMimeData容器中
QString text = theDragItem->text();
QIcon icon = theDragItem->Img;
QIcon icon_hover = theDragItem->Img_hover;
QByteArray itemData;
QDataStream dataStream(&itemData, QIODevice::WriteOnly);
dataStream << text << icon << icon_hover;
QMimeData *mimeData = new QMimeData;
mimeData->setData(myMimeType(), itemData);
//[1]
//[2]设置拖拽时的缩略图
thumbnail *DragImage = new thumbnail(this);
DragImage->setupthumbnail(icon_hover, text);
//DragImage->setIconSize(18); //default:20
QPixmap pixmap = DragImage->grab();
QDrag *drag = new QDrag(this);
drag->setMimeData(mimeData);
drag->setPixmap(pixmap);
drag->setHotSpot(QPoint(pixmap.width() / 2, pixmap.height() / 2));
//[2]
//删除的行需要根据theInsertRow和theDragRow的大小关系来判断(这个也是我根据实际情况测试发现的)
if(drag->exec(Qt::MoveAction) == Qt::MoveAction){
int theRemoveRow = -1;
if(theInsertRow < theDragRow) theRemoveRow = theDragRow + 1;
else theRemoveRow = theDragRow;
model()->removeRow(theRemoveRow);
}
}
}
void TestListView::dragEnterEvent(QDragEnterEvent *event)
{
TestListView *source = qobject_cast<TestListView *>(event->source());
if (source && source == this) {
//IsDraging(标志位)判断是否正在拖拽
IsDraging = true;
event->setDropAction(Qt::MoveAction);
event->accept();
}
}
void TestListView::dragLeaveEvent(QDragLeaveEvent *event)
{
oldHighlightedRow = theHighlightedRow;
theHighlightedRow = -2;
//之前QListWidget用的是update(QRect)，这里用的是update(QModelIndex)，当然这里也可以使用update(QRect)，只是想换一种方法而已
update(model()->index(oldHighlightedRow, 0)); //UpRow
update(model()->index(oldHighlightedRow + 1, 0)); //DownRow
IsDraging = false; //IsDraging(标志位)判断是否正在拖拽
theInsertRow = -1;
event->accept();
}
void TestListView::dragMoveEvent(QDragMoveEvent *event)
{
TestListView *source = qobject_cast<TestListView *>(event->source());
if (source && source == this) {
oldHighlightedRow = theHighlightedRow;
theHighlightedRow = indexAt(event->pos() - QPoint(0, offset())).row();
//offset() = 19 = 40 / 2 - 1，其中40是行高
if(event->pos().y() >= offset()){
if(oldHighlightedRow != theHighlightedRow){
//刷新旧区域使dropIndicator消失
update(model()->index(oldHighlightedRow, 0));
update(model()->index(oldHighlightedRow + 1, 0));
//刷新新区域使dropIndicator显示
update(model()->index(theHighlightedRow, 0));
update(model()->index(theHighlightedRow + 1, 0));
}else{
update(model()->index(theHighlightedRow, 0));
update(model()->index(theHighlightedRow + 1, 0));
}
theInsertRow = theHighlightedRow + 1;
}else{
theHighlightedRow = -1;
update(model()->index(0, 0));
update(model()->index(1, 0));
theInsertRow = 0;
}
event->setDropAction(Qt::MoveAction);
event->accept();
}
}
void TestListView::dropEvent(QDropEvent *event)
{
TestListView *source = qobject_cast<TestListView *>(event->source());
if (source && source == this){
IsDraging = false; //IsDraging(标志位)判断是否正在拖拽
oldHighlightedRow = theHighlightedRow;
theHighlightedRow = -2;
//刷新旧区域使dropIndicator消失
update(model()->index(oldHighlightedRow, 0));
update(model()->index(oldHighlightedRow + 1, 0));
if(theInsertRow == theDragRow || theInsertRow == theDragRow + 1) return;
//这里我像QListWidget那样调用父类dropEvent(event)发现不起作用(原因尚不明)，没办法，只能删除旧行，插入新行
//if(theSelectedRow == theDragRow){
//QListView::dropEvent(event);
//return;
//}
QString text;
QIcon icon, icon_hover;
QByteArray itemData = event->mimeData()->data(myMimeType());
QDataStream dataStream(&itemData, QIODevice::ReadOnly);
dataStream >> text >> icon >> icon_hover;
model()->insertRow(theInsertRow);
QStandardItemModel *listModel = qobject_cast<QStandardItemModel *>(model());
listModel->setItem(theInsertRow, 0, new TestListViewItem(icon, icon_hover, text));
setCurrentIndex(model()->index(theInsertRow, 0)); //插入行保持选中状态
event->setDropAction(Qt::MoveAction);
event->accept();
}
}
（3）TestItemDelegate类继承自QStyledItemDelegate，主要是为了绘制dropIndicator。图示为dropIndicator组成：
- QStyledItemDelegate.h文件：
#define POLYGON 4 //等腰三角形直角边长
#define WIDTH 1 //分隔符粗细的一半
class TestItemDelegate : public QStyledItemDelegate
{
Q_OBJECT
public:
TestItemDelegate(QObject *parent = nullptr);
protected:
void paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const;
};
- QStyledItemDelegate.c文件：
TestItemDelegate::TestItemDelegate(QObject *parent)
: QStyledItemDelegate(parent)
{
}
void TestItemDelegate::paint(QPainter * painter, const QStyleOptionViewItem & option, const QModelIndex & index) const
{
TestListView *dragView = qobject_cast<TestListView *>(option.styleObject);
bool isDraging = dragView->isDraging();
QRect rect = option.rect;
painter->setRenderHint(QPainter::Antialiasing, true);
painter->setPen(Qt::NoPen);
if(option.state & (QStyle::State_MouseOver | QStyle::State_Selected)){
QStandardItemModel *listModel = qobject_cast<QStandardItemModel *>(dragView->model());
TestListViewItem *item = static_cast<TestListViewItem *>(listModel->item(index.row()));
item->setIcon(item->Img_hover);
if(option.state & QStyle::State_MouseOver){
}
if(option.state & QStyle::State_Selected){
painter->setBrush(QColor(180, 0, 0));
painter->drawRect(rect.topLeft().x(), rect.topLeft().y(), 4, rect.height());
painter->setBrush(QColor(230, 231, 234));
painter->drawRect(rect.topLeft().x() + 4, rect.topLeft().y(), rect.width() - 4, rect.height());
}
}else{
QStandardItemModel *listModel = qobject_cast<QStandardItemModel *>(dragView->model());
TestListViewItem *item = static_cast<TestListViewItem *>(listModel->item(index.row()));
item->setIcon(item->Img);
}
//begin drag
if(isDraging){
int theDragRow = dragView->dragRow();
int UpRow = dragView->highlightedRow();
int DownRow = UpRow + 1;
int rowCount = dragView->model()->rowCount() - 1;
//绘制DropIndicator
if(index.row() == UpRow && index.row() != theDragRow - 1 && index.row() != theDragRow){
painter->setBrush(QColor(66, 133, 244));
if(UpRow == rowCount){
//到达尾部,三角形向上移动一个WIDTH的距离,以使分隔符宽度*2
QPolygon trianglePolygon_bottomLeft;
trianglePolygon_bottomLeft << QPoint(rect.bottomLeft().x(), rect.bottomLeft().y() - (POLYGON + WIDTH) + 1 - WIDTH);
trianglePolygon_bottomLeft << QPoint(rect.bottomLeft().x(), rect.bottomLeft().y() - WIDTH + 1 - WIDTH);
trianglePolygon_bottomLeft << QPoint(rect.bottomLeft().x() + POLYGON, rect.bottomLeft().y() - WIDTH + 1 - WIDTH);
QPolygon trianglePolygon_bottomRight;
trianglePolygon_bottomRight << QPoint(rect.bottomRight().x() + 1, rect.bottomRight().y() - (POLYGON + WIDTH) + 1 - WIDTH);
trianglePolygon_bottomRight << QPoint(rect.bottomRight().x() + 1, rect.bottomRight().y() - WIDTH + 1 - WIDTH);
trianglePolygon_bottomRight << QPoint(rect.bottomRight().x() - POLYGON + 1, rect.bottomRight().y() - WIDTH + 1 - WIDTH);
painter->drawRect(rect.bottomLeft().x(), rect.bottomLeft().y() - 2 * WIDTH + 1, rect.width(), 2 * WIDTH); //rect
painter->drawPolygon(trianglePolygon_bottomLeft);
painter->drawPolygon(trianglePolygon_bottomRight);
}
else {
//正常情况,组成上半部分(+1是根据实际情况修正)
QPolygon trianglePolygon_bottomLeft;
trianglePolygon_bottomLeft << QPoint(rect.bottomLeft().x(), rect.bottomLeft().y() - (POLYGON + WIDTH) + 1);
trianglePolygon_bottomLeft << QPoint(rect.bottomLeft().x(), rect.bottomLeft().y() - WIDTH + 1);
trianglePolygon_bottomLeft << QPoint(rect.bottomLeft().x() + POLYGON, rect.bottomLeft().y() - WIDTH + 1);
QPolygon trianglePolygon_bottomRight;
trianglePolygon_bottomRight << QPoint(rect.bottomRight().x() + 1, rect.bottomRight().y() - (POLYGON + WIDTH) + 1);
trianglePolygon_bottomRight << QPoint(rect.bottomRight().x() + 1, rect.bottomRight().y() - WIDTH + 1);
trianglePolygon_bottomRight << QPoint(rect.bottomRight().x() - POLYGON + 1, rect.bottomRight().y() - WIDTH + 1);
painter->drawRect(rect.bottomLeft().x(), rect.bottomLeft().y() - WIDTH + 1, rect.width(), WIDTH); //rect
painter->drawPolygon(trianglePolygon_bottomLeft);
painter->drawPolygon(trianglePolygon_bottomRight);
}
}
else if(index.row() == DownRow && index.row() != theDragRow + 1 && index.row() != theDragRow){
painter->setBrush(QColor(66, 133, 244));
if(DownRow == 0){
//reach the head
QPolygon trianglePolygon_topLeft;
trianglePolygon_topLeft << QPoint(rect.topLeft().x(), rect.topLeft().y() + (POLYGON + WIDTH) + WIDTH);
trianglePolygon_topLeft << QPoint(rect.topLeft().x(), rect.topLeft().y() + WIDTH + WIDTH);
trianglePolygon_topLeft << QPoint(rect.topLeft().x() + POLYGON, rect.topLeft().y() + WIDTH + WIDTH);
QPolygon trianglePolygon_topRight;
trianglePolygon_topRight << QPoint(rect.topRight().x() + 1, rect.topRight().y() + (POLYGON + WIDTH) + WIDTH);
trianglePolygon_topRight << QPoint(rect.topRight().x() + 1, rect.topRight().y() + WIDTH + WIDTH);
trianglePolygon_topRight << QPoint(rect.topRight().x() - POLYGON + 1, rect.topRight().y() + WIDTH + WIDTH);
painter->drawRect(rect.topLeft().x(), rect.topLeft().y(), rect.width(), 2 * WIDTH); //rect
painter->drawPolygon(trianglePolygon_topLeft);
painter->drawPolygon(trianglePolygon_topRight);
}
else{
//normal
QPolygon trianglePolygon_topLeft;
trianglePolygon_topLeft << QPoint(rect.topLeft().x(), rect.topLeft().y() + (POLYGON + WIDTH));
trianglePolygon_topLeft << QPoint(rect.topLeft().x(), rect.topLeft().y() + WIDTH);
trianglePolygon_topLeft << QPoint(rect.topLeft().x() + POLYGON, rect.topLeft().y() + WIDTH);
QPolygon trianglePolygon_topRight;
trianglePolygon_topRight << QPoint(rect.topRight().x() + 1, rect.topRight().y() + (POLYGON + WIDTH));
trianglePolygon_topRight << QPoint(rect.topRight().x() + 1, rect.topRight().y() + WIDTH);
trianglePolygon_topRight << QPoint(rect.topRight().x() - POLYGON + 1, rect.topRight().y() + WIDTH);
painter->drawRect(rect.topLeft().x(), rect.topLeft().y(), rect.width(), WIDTH); //rect
painter->drawPolygon(trianglePolygon_topLeft);
painter->drawPolygon(trianglePolygon_topRight);
}
}
QStyledItemDelegate::paint(painter, option, index);
return;
}
//end drag
QStyledItemDelegate::paint(painter, option, index);
}
（4）使用TestListViewItem、TestListView和TestItemDelegate
- 主窗口.h文件：
class test : public QWidget
{
Q_OBJECT
public:
explicit test(QWidget *parent = nullptr);
private:
void initUi();
};
- 主窗口.c文件：
test::test(QWidget *parent) : QWidget(parent)
{
initUi();
}
void test::initUi()
{
setFixedSize(250, 600);
QStandardItemModel *listModel = new QStandardItemModel();
listModel->setItem(0, 0, new TestListViewItem(QIcon(":/listBar_Icon/1.png"), QIcon(":/listBar_Icon/1_hover.png"), "发现音乐"));
listModel->setItem(1, 0, new TestListViewItem(QIcon(":/listBar_Icon/2.png"), QIcon(":/listBar_Icon/2_hover.png"), "私人FM"));
listModel->setItem(2, 0, new TestListViewItem(QIcon(":/listBar_Icon/3.png"), QIcon(":/listBar_Icon/3_hover.png"), "朋友"));
listModel->setItem(3, 0, new TestListViewItem(QIcon(":/listBar_Icon/4.png"), QIcon(":/listBar_Icon/4_hover.png"), "MV"));
listModel->setItem(4, 0, new TestListViewItem(QIcon(":/listBar_Icon/5.png"), QIcon(":/listBar_Icon/5_hover.png"), "本地音乐"));
listModel->setItem(5, 0, new TestListViewItem(QIcon(":/listBar_Icon/6.png"), QIcon(":/listBar_Icon/6_hover.png"), "下载管理"));
listModel->setItem(6, 0, new TestListViewItem(QIcon(":/listBar_Icon/7.png"), QIcon(":/listBar_Icon/7_hover.png"), "我的音乐云盘"));
listModel->setItem(7, 0, new TestListViewItem(QIcon(":/listBar_Icon/8.png"), QIcon(":/listBar_Icon/8_hover.png"), "我的收藏"));
TestListView *listView = new TestListView(this);
listView->setIconSize(QSize(25, 25));
listView->setFocusPolicy(Qt::NoFocus); //这样可禁用tab键和上下方向键并且除去复选框
listView->setFixedHeight(320);
listView->setFont(QFont("宋体", 10, QFont::DemiBold));
listView->setStyleSheet(
//"*{outline:0px;}" //除去复选框
"QListView{background:rgb(245, 245, 247); border:0px; margin:0px 0px 0px 0px;}"
"QListView::Item{height:40px; border:0px; padding-left:14px; color:rgba(200, 40, 40, 255);}"
"QListView::Item:hover{color:rgba(40, 40, 200, 255); padding-left:14px;}"
"QListView::Item:selected{color:rgba(40, 40, 200, 255); padding-left:15px;}"
);
TestItemDelegate *delegate = new TestItemDelegate();
listView->setItemDelegate(delegate);
listView->setModel(listModel);
QVBoxLayout *layout = new QVBoxLayout(this);
layout->setSpacing(0);
layout->addWidget(listView);
layout->setContentsMargins(0, 0, 0, 0);
setLayout(layout);
}
如果想要接触更多关于拖拽的代码，在Qt例程中搜索“drag”。推荐看一下例程puzzle的两种实现方法（一种是继承QListWidget，另一种是QListView + 继承QAbstractListModel）。
| 环境配置 ：MinGW + QT 5.12 |