QML GridView doesn't reflect changes in C++ model - c++

Question

I follow the Using C++ Models with Qt Quick Views and AbstractItemModel example project in Qt 5.5. Screen class is the model data; ScreenManager is derived from QAbstractListModel acting as the model source in QML GridView. In the GridView, I also add a MouseArea and some animation in delegate to implement items drag and drop.
My expected result is when dragging a screen around, whenever it's on top of another screen, the target screen will be moved to the last position of dragged screen until button release to drop the dragged screen. All the movement should use the animation declared in QML.
Now it could show screens correctly and recognize the selected screen. But it fails to swap the dragged and dropped screens. The underlying list has swapped the element but it doesn't reflect to the view.
A similar question is this, I try to use beginMoveRows and endMoveRows. But my program crashes on calling endMoveRows. layoutChanged would rearrange the whole model. Because I have animation on grid item movement. layoutChanged would cause non affected screens shifting from top left to their original position.
Edit: endMoveRows crash is caused by invalid operation described here.
Edit: the GridView has a 3 * 5 items. Since it's in a QList, I assume I only need to move on rows.
Screen.h
class Screen
{
public:
Screen(QString name, int gridId, bool active = false);
QString name() const;
int gridId() const;
bool active() const;
void setActive(bool a);
private:
QString m_name;
int m_gridId;
bool m_active;
};
ScreenManager.h
#include "Screen.h"
#include <QAbstractListModel>
class ScreenManager : public QAbstractListModel
{
Q_OBJECT
public:
enum ScreenRoles {
NameRole = Qt::UserRole + 1,
GridIDRole,
ActiveRole
};
ScreenManager();
void addScreen(const Screen& screen);
int rowCount(const QModelIndex& parent = QModelIndex()) const;
QVariant data(const QModelIndex& index, int role = Qt::DisplayRole) const;
Q_INVOKABLE int getScreenGridId(int index);
Q_INVOKABLE bool getScreenActive(int index);
Q_INVOKABLE void swapScreens(int index1, int index2);
protected:
QHash<int, QByteArray> roleNames() const;
private:
QList<Screen> m_screens;
};
ScreenManager.cpp
#include "ScreenManager.h"
#include "Screen.h"
ScreenManager::ScreenManager()
{
int index = 0;
for (;index < 15; index++) {
addScreen(Screen(QString ("Screen%1").arg(index), index, true));
}
}
void ScreenManager::addScreen(const Screen& screen)
{
beginInsertRows(QModelIndex(), rowCount(), rowCount());
m_screens << screen;
endInsertRows();
}
int ScreenManager::rowCount(const QModelIndex& parent) const {
Q_UNUSED(parent);
return m_screens.count();
}
QVariant ScreenManager::data(const QModelIndex& index, int role) const
{
if (index.row() < 0 || index.row() >= m_screens.count())
return QVariant();
const Screen& screen = m_screens[index.row()];
if (role == NameRole)
return screen.name();
else if (role == GridIDRole)
return screen.gridId();
else if (role == ActiveRole)
return screen.active();
return QVariant();
}
QHash<int, QByteArray> ScreenManager::roleNames() const
{
QHash<int, QByteArray> roles;
roles[NameRole] = "name";
roles[GridIDRole] = "gridId";
roles[ActiveRole] = "active";
return roles;
}
int ScreenManager::getScreenGridId(int index)
{
return m_screens.at(index).gridId();
}
bool ScreenManager::getScreenActive(int index)
{
return m_screens.at(index).active();
}
void ScreenManager::swapScreens(int index1, int index2)
{
int min = index1 < index2 ? index1 : index2;
int max = index1 > index2 ? index1 : index2;
bool r = beginMoveRows(QModelIndex(), min, min, QModelIndex(), max);
r = beginMoveRows(QModelIndex(), max-1, max-1, QModelIndex(), min);
m_screens.swap(index1, index2);
endMoveRows();
}
QML GridView related code
ScreenManager {
id : screenManager
}
GridView {
id: gridView
x: 82
y: 113
width: cellWidth * 5
height: cellHeight * 3
clip: true
anchors.bottom: parent.bottom
anchors.bottomMargin: 70
anchors.topMargin: 100
anchors.horizontalCenter: parent.horizontalCenter
anchors.top: parent.top
flickableDirection: Flickable.HorizontalAndVerticalFlick
cellWidth: 90; cellHeight: 90;
property bool ignoreMovementAnimation: true
MouseArea {
id: gridViewMouseArea
hoverEnabled: true
preventStealing : true
property int currentGridId: -1
property int preIndex
property int index: gridView.indexAt(mouseX, mouseY)
anchors.fill: parent
onPressAndHold: {
currentGridId = screenManager.getScreenGridId(index)
preIndex = index
preIndexBackup = preIndex
gridView.ignoreMovementAnimation = false
}
onReleased: currentGridId = -1
onPositionChanged: {
if (currentGridId != -1 && index != -1 && index != preIndex) {
if (screenManager.getScreenActive(index)) {
screenManager.swapScreens(preIndex, index)
preIndex = index
}
}
}
}
model: screenManager
delegate: Component {
Item {
id: gridViewDelegate
width: gridView.cellWidth; height: gridView.cellHeight
Image {
id: itemImage
parent: gridView
x: gridViewDelegate.x + 5
y: gridViewDelegate.y + 5
width: gridViewDelegate.width - 10
height: gridViewDelegate.height - 10;
fillMode: Image.PreserveAspectFit
smooth: true
source: "qrc:/res/image/screen_icon.png"
visible: active
Text {
text: name
anchors.horizontalCenter: parent.horizontalCenter
anchors.verticalCenter: parent.verticalCenter
}
Rectangle {
anchors.fill: parent;
border.color: "grey"
border.width: 6
color: "transparent"; radius: 5
visible: itemImage.state === "active"
}
// specify the movement's animation for non-active screen icons
Behavior on x {
enabled: !gridView.ignoreMovementAnimation && itemImage.state !== "active"
NumberAnimation { duration: 400; easing.type: Easing.OutBack }
}
Behavior on y {
enabled: !gridView.ignoreMovementAnimation && itemImage.state !== "active"
NumberAnimation { duration: 400; easing.type: Easing.OutBack }
}
// specify the shaking animation for non-active screen icons when hold one icon
SequentialAnimation on rotation {
NumberAnimation { to: 2; duration: 60 }
NumberAnimation { to: -2; duration: 120 }
NumberAnimation { to: 0; duration: 60 }
running: gridViewMouseArea.currentGridId != -1 && itemImage.state !== "active"
loops: Animation.Infinite
alwaysRunToEnd: true
}
// specify the active screen's new position and size
states: State {
name: "active"
when: gridViewMouseArea.currentGridId == gridId
PropertyChanges {
target: itemImage
x: gridViewMouseArea.mouseX - width/2
y: gridViewMouseArea.mouseY - height/2
scale: 0.5
z: 10
}
}
// specify the scale speed for the active screen icon
transitions: Transition {
NumberAnimation { property: "scale"; duration: 200}
}
}
}
}
}
main.cpp
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
qmlRegisterType<ScreenManager>("com.gui", 1, 0, "ScreenManager");
QQmlApplicationEngine engine(QUrl(QStringLiteral("qrc:/main.qml")));
return app.exec();
}

Answer 1

It turns out I need to deal some corner cases to avoid no-op or invalid move operation.
void ScreenManager::swapScreens(int index1, int index2)
{
int min = index1 < index2 ? index1 : index2;
int max = index1 > index2 ? index1 : index2;
m_screens.swap(index1, index2);
beginMoveRows(QModelIndex(), max, max, QModelIndex(), min);
endMoveRows();
if (max - min > 1) {
beginMoveRows(QModelIndex(), min + 1, min + 1, QModelIndex(), max + 1);
endMoveRows();
}
}