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29 \example itemviews/spinboxdelegate
30 \title Spin Box Delegate Example
32 The Spin Box Delegate example shows how to create an editor for a custom delegate in
33 the model/view framework by reusing a standard Qt editor widget.
35 The model/view framework provides a standard delegate that is used by default
36 with the standard view classes. For most purposes, the selection of editor
37 widgets available through this delegate is sufficient for editing text, boolean
38 values, and other simple data types. However, for specific data types, it is
39 sometimes necessary to use a custom delegate to either display the data in a
40 specific way, or allow the user to edit it with a custom control.
42 \image spinboxdelegate-example.png
44 This concepts behind this example are covered in the
45 \l{Model/View Programming#Delegate Classes}{Delegate Classes} chapter
46 of the \l{Model/View Programming} overview.
48 \section1 SpinBoxDelegate Class Definition
50 The definition of the delegate is as follows:
52 \snippet examples/itemviews/spinboxdelegate/delegate.h 0
54 The delegate class declares only those functions that are needed to
55 create an editor widget, display it at the correct location in a view,
56 and communicate with a model. Custom delegates can also provide their
57 own painting code by reimplementing the \c paintEvent() function.
58 Furthermore it is also possible to reuse (and avoid deleting) the editor
59 widget by reimplementing the \a destroyEditor() function. A reused widget
60 could be a mutable member created in the constructor and deleted in
63 \section1 SpinBoxDelegate Class Implementation
65 Delegates are often stateless. The constructor only needs to
66 call the base class's constructor with the parent QObject as its
69 \snippet examples/itemviews/spinboxdelegate/delegate.cpp 0
71 Since the delegate is a subclass of QItemDelegate, the data it retrieves
72 from the model is displayed in a default style, and we do not need to
73 provide a custom \c paintEvent().
75 The \c createEditor() function returns an editor widget, in this case a
76 spin box that restricts values from the model to integers from 0 to 100
79 \snippet examples/itemviews/spinboxdelegate/delegate.cpp 1
81 We install an event filter on the spin box to ensure that it behaves in
82 a way that is consistent with other delegates. The implementation for
83 the event filter is provided by the base class.
85 The \c setEditorData() function reads data from the model, converts it
86 to an integer value, and writes it to the editor widget.
88 \snippet examples/itemviews/spinboxdelegate/delegate.cpp 2
90 Since the view treats delegates as ordinary QWidget instances, we have
91 to use a static cast before we can set the value in the spin box.
93 The \c setModelData() function reads the contents of the spin box, and
94 writes it to the model.
96 \snippet examples/itemviews/spinboxdelegate/delegate.cpp 3
98 We call \l{QSpinBox::interpretText()}{interpretText()} to make sure that
99 we obtain the most up-to-date value in the spin box.
101 The \c updateEditorGeometry() function updates the editor widget's
102 geometry using the information supplied in the style option. This is the
103 minimum that the delegate must do in this case.
105 \snippet examples/itemviews/spinboxdelegate/delegate.cpp 4
107 More complex editor widgets may divide the rectangle available in
108 \c{option.rect} between different child widgets if required.
110 \section1 The Main Function
112 This example is written in a slightly different way to many of the
113 other examples supplied with Qt. To demonstrate the use of a custom
114 editor widget in a standard view, it is necessary to set up a model
115 containing some arbitrary data and a view to display it.
117 We set up the application in the normal way, construct a standard item
118 model to hold some data, set up a table view to use the data in the
119 model, and construct a custom delegate to use for editing:
121 \snippet examples/itemviews/spinboxdelegate/main.cpp 0
123 The table view is informed about the delegate, and will use it to
124 display each of the items. Since the delegate is a subclass of
125 QItemDelegate, each cell in the table will be rendered using standard
128 We insert some arbitrary data into the model for demonstration purposes:
130 \snippet examples/itemviews/spinboxdelegate/main.cpp 1
131 \snippet examples/itemviews/spinboxdelegate/main.cpp 2
133 Finally, the table view is displayed with a window title, and we start
134 the application's event loop:
136 \snippet examples/itemviews/spinboxdelegate/main.cpp 3
138 Each of the cells in the table can now be edited in the usual way, but
139 the spin box ensures that the data returned to the model is always
140 constrained by the values allowed by the spin box delegate.