Due to lack of any other Qt demo, I am making use of Qt widgets's SimpleTreeModel
demo to implement C++ model for my QML TreeView. I have defined roles so QML can use it but I am having trouble connecting them with actual model data.
What I also find interesting is that widgets (C++) demo works fine but I figured this out, every TreeItem store all its child items and TreeModel has only one TreeModel
doesn't seem to store the data as its member variable..leaves me scratching my head.rootItem
which in turn stores all data as its child.
The TreeItem class
class TreeItem
{
public:
explicit TreeItem(const QList<QVariant> &data, TreeItem *parentItem = 0);
~TreeItem();
void appendChild(TreeItem *child);
TreeItem *child(int row);
int childCount() const;
int columnCount() const;
QVariant data(int column) const;
int row() const;
TreeItem *parentItem();
private:
QList<TreeItem*> m_childItems;
QList<QVariant> m_itemData;
TreeItem *m_parentItem;
};
The TreeModel class
class TreeModel : public QAbstractItemModel
{
Q_OBJECT
public:
enum DisplayRoles {
TitleRole = Qt::UserRole + 1,
SummaryRole
};
explicit TreeModel(const QString &data, QObject *parent = 0);
~TreeModel();
QVariant data(const QModelIndex &index, int role) const Q_DECL_OVERRIDE;
Qt::ItemFlags flags(const QModelIndex &index) const Q_DECL_OVERRIDE;
QVariant headerData(int section, Qt::Orientation orientation,
int role = Qt::DisplayRole) const Q_DECL_OVERRIDE;
QModelIndex index(int row, int column,
const QModelIndex &parent = QModelIndex()) const Q_DECL_OVERRIDE;
QModelIndex parent(const QModelIndex &index) const Q_DECL_OVERRIDE;
int rowCount(const QModelIndex &parent = QModelIndex()) const Q_DECL_OVERRIDE;
int columnCount(const QModelIndex &parent = QModelIndex()) const Q_DECL_OVERRIDE;
QHash<int, QByteArray> TreeModel::roleNames() const {
QHash<int, QByteArray> roles;
roles[TitleRole] = "title";
roles[SummaryRole] = "summary";
return roles;
}
private:
void setupModelData(const QStringList &lines, TreeItem *parent);
TreeItem *rootItem;
};
The model loads the data from a default.txt
TreeModel::TreeModel(const QString &data, QObject *parent)
: QAbstractItemModel(parent)
{
QList<QVariant> rootData;
rootData << "Title" << "Summary";
rootItem = new TreeItem(rootData);
setupModelData(data.split(QString("\n")), rootItem);
}
void TreeModel::setupModelData(const QStringList &lines, TreeItem *parent)
{
QList<TreeItem*> parents;
QList<int> indentations;
parents << parent;
indentations << 0;
int number = 0;
while (number < lines.count()) {
int position = 0;
while (position < lines[number].length()) {
if (lines[number].mid(position, 1) != " ")
break;
position++;
}
QString lineData = lines[number].mid(position).trimmed();
if (!lineData.isEmpty()) {
// Read the column data from the rest of the line.
QStringList columnStrings = lineData.split("\t", QString::SkipEmptyParts);
QList<QVariant> columnData;
for (int column = 0; column < columnStrings.count(); ++column)
columnData << columnStrings[column];
if (position > indentations.last()) {
// The last child of the current parent is now the new parent
// unless the current parent has no children.
if (parents.last()->childCount() > 0) {
parents << parents.last()->child(parents.last()->childCount()-1);
indentations << position;
}
} else {
while (position < indentations.last() && parents.count() > 0) {
parents.pop_back();
indentations.pop_back();
}
}
// Append a new item to the current parent's list of children.
parents.last()->appendChild(new TreeItem(columnData, parents.last()));
}
++number;
}
}
My problem is in this function, how do I connect the roles with the data which is stored in rootItem
?. Note titleString
and summaryString
are possible proposed functions (if needed) but I don't know what to write in them get access the data!
QVariant TreeModel::data(const QModelIndex &index, int role) const
{
if (!index.isValid())
return QVariant();
if (index.isValid() && role >= TitleRole) {
switch (role) {
case TitleRole:
return QVariant(titleString(rootItem(index))); // get title through rootItem?
case SummaryRole:
return QVariant(summaryString(rootItem(index))); // get summary through rootItem?
}
}
if (role != Qt::DisplayRole)
return QVariant();
TreeItem *item = static_cast<TreeItem*>(index.internalPointer());
return item->data(index.column());
}
The default.txt
has the following data but the same is available in the Qt Creator demo itself as well.
Getting Started How to familiarize yourself with Qt Designer
Launching Designer Running the Qt Designer application
The User Interface How to interact with Qt Designer
Designing a Component Creating a GUI for your application
Creating a Dialog How to create a dialog
Composing the Dialog Putting widgets into the dialog example
Creating a Layout Arranging widgets on a form
Signal and Slot Connections Making widget communicate with each other
Using a Component in Your Application Generating code from forms
The Direct Approach Using a form without any adjustments
The Single Inheritance Approach Subclassing a form's base class
The Multiple Inheritance Approach Subclassing the form itself
Automatic Connections Connecting widgets using a naming scheme
A Dialog Without Auto-Connect How to connect widgets without a naming scheme
A Dialog With Auto-Connect Using automatic connections
Form Editing Mode How to edit a form in Qt Designer
Managing Forms Loading and saving forms
Editing a Form Basic editing techniques
The Property Editor Changing widget properties
The Object Inspector Examining the hierarchy of objects on a form
Layouts Objects that arrange widgets on a form
Applying and Breaking Layouts Managing widgets in layouts
Horizontal and Vertical Layouts Standard row and column layouts
The Grid Layout Arranging widgets in a matrix
Previewing Forms Checking that the design works
Using Containers How to group widgets together
General Features Common container features
Frames QFrame
Group Boxes QGroupBox
Stacked Widgets QStackedWidget
Tab Widgets QTabWidget
Toolbox Widgets QToolBox
Connection Editing Mode Connecting widgets together with signals and slots
Connecting Objects Making connections in Qt Designer
Editing Connections Changing existing connections
My output shows the same number of lines as in widgets demo except that there is no text. It seems like it is just not connected to the roles properly or roles are not connected to day. I am attaching the screen shot of my output.
Just so if anyone is trying to do the same thing, I figured it out and here is the answer. The data method of the model should read the following.
QVariant TreeModel::data(const QModelIndex &index, int role) const
{
if (!index.isValid())
return QVariant();
TreeItem *item = static_cast<TreeItem*>(index.internalPointer());
if (index.isValid() && role >= TitleRole) {
switch (role) {
case TitleRole:
return item->data(0);
case SummaryRole:
return item->data(1);
}
}
if (role != Qt::DisplayRole)
return QVariant();
return item->data(index.column());
}
TreeItem
could be changed in real application to store specific data in which case the above method will point to that data instead of column number approach.