Color Editor Factory Example¶
This example shows how to create an editor that can be used by a
QItemDelegate
.When editing data in a
QListView
,QTableView
, orQTreeView
, editors are created and displayed by a delegate .QItemDelegate
, which is the default delegate used by Qt’s item views , uses aQItemEditorFactory
to create editors for it. A unique instance provided byQItemEditorFactory
is by default installed on all item delegates.An item editor factory contains a collection of
QItemEditorCreatorBase
instances, which are specialized factories that produce editors for one particularQVariant
data type (all models in Qt store their data inQVariant
s). An editor can be any Qt or custom widget.In this example, we will create an editor (implemented in the
ColorListEditor
class) that can edit theQColor
data type and be used byQItemDelegate
s. We do this by creating a newQItemEditorCreatorBase
that producesColorListEditors
and register it with a new factory, which we set as the default editor item factory (the unique factory instance). To test our editor, we have implemented theWindow
class, which displays aQTableWidget
in whichQColor
s can be edited.
Window Class Implementation¶
In the Window class, we create the item editor creator base for our color editor and add it to the default factory. We also create a
QTableWidget
in which our editor can be tested. It is filled with some data and displayed in a window.We take a closer look at the constructor:
Window::Window() { QItemEditorFactory *factory = new QItemEditorFactory; QItemEditorCreatorBase *colorListCreator = new QStandardItemEditorCreator<ColorListEditor>(); factory->registerEditor(QMetaType::QColor, colorListCreator); QItemEditorFactory::setDefaultFactory(factory); createGUI(); }The
QStandardItemEditorCreator
is a convenience class that inheritsQItemEditorCreatorBase
. Its constructor takes a template class, of which instances are returned fromcreateWidget()
. The creator uses a constructor that takes aQWidget
as its only parameter; the template class must provide this. This way, there is no need to subclassQStandardItemEditorCreator
.After the new factory has been set, all standard item delegates will use it (i.e, also delegates that were created before the new default factory was set).
The
createGUI()
function sets up the table and fills it with data.
ColorListEditor Definition¶
The ColorListEditor inherits
QComboBox
and lets the user select aQColor
from its popup list.class ColorListEditor : public QComboBox { Q_OBJECT Q_PROPERTY(QColor color READ color WRITE setColor USER true) public: ColorListEditor(QWidget *widget = nullptr); public: QColor color() const; void setColor(const QColor &color); private: void populateList(); };
QItemDelegate
manages the interaction between the editor and the model, i.e., it retrieves data to edit from the model and store data from the editor in the model. The data that is edited by an editor is stored in the editor’s user data property, and the delegate uses Qt’s property system to access it by name. We declare our user data property with theQ_PROPERTY
macro. The property is set to be the user type with the USER keyword.
ColorListEditor Implementation¶
The constructor of
ColorListEditor
simply callspopulateList()
, which we will look at later. We move on to thecolor()
function:QColor ColorListEditor::color() const { return qvariant_cast<QColor>(itemData(currentIndex(), Qt::DecorationRole)); }We return the data that is selected in the combobox. The data is stored in the
DecorationRole
as the color is then also displayed in the popup list (as shown in the image above).void ColorListEditor::setColor(const QColor &color) { setCurrentIndex(findData(color, Qt::DecorationRole)); }The
findData()
function searches the items in the combobox and returns the index of the item that hascolor
in the Qt::Decoration role.void ColorListEditor::populateList() { const QStringList colorNames = QColor::colorNames(); for (int i = 0; i < colorNames.size(); ++i) { QColor color(colorNames[i]); insertItem(i, colorNames[i]); setItemData(i, color, Qt::DecorationRole); } }Qt knows some predefined colors by name. We simply loop through these to fill our editor with items.
Further Customization of Item View Editors¶
You can customize Qt’s model view framework in many ways. The procedure shown in this example is usually sufficient to provide custom editors. Further customization is achieved by subclassing
QItemEditorFactory
andQItemEditorCreatorBase
. It is also possible to subclassQItemDelegate
if you don’t wish to use a factory at all.Possible suggestions are:
If the editor widget has no user property defined, the delegate asks the factory for the property name, which it in turn asks the item editor creator for. In this case, you can use the
QItemEditorCreator
class, which takes the property name to use for editing as a constructor argument.If the editor requires other constructors or other initialization than provided by
QItemEditorCreatorBase
, you must reimplementcreateWidget()
.You could also subclass
QItemEditorFactory
if you only want to provide editors for certain kinds of data or use another method of creating the editors than using creator bases.In this example, we use a standard
QVariant
data type. You can also use custom types. In the Star Delegate Example , we show how to store a custom data type in aQVariant
and paint and edit it in a class that inheritsQItemDelegate
.
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