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125 lines
5.0 KiB
Plaintext
125 lines
5.0 KiB
Plaintext
// Copyright (C) 2016 The Qt Company Ltd.
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// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
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/*!
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\example layouts/flowlayout
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\title Flow Layout Example
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\examplecategory {User Interface Components}
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\ingroup examples-layout
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\brief Shows how to arrange widgets for different window sizes.
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\e{Flow Layout} implements a layout that handles different window sizes. The
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widget placement changes depending on the width of the application window.
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\image flowlayout-example.png Screenshot of the Flow Layout example
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The Flowlayout class mainly uses QLayout and QWidgetItem, while the
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Window uses QWidget and QLabel.
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For more information, visit the \l{Layout Management} page.
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\include examples-run.qdocinc
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\section1 FlowLayout Class Definition
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The \c FlowLayout class inherits QLayout. It is a custom layout class
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that arranges its child widgets horizontally and vertically.
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\snippet layouts/flowlayout/flowlayout.h 0
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We reimplement functions inherited from QLayout. These functions add items to
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the layout and handle their orientation and geometry.
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We also declare two private methods, \c doLayout() and \c smartSpacing().
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\c doLayout() lays out the layout items, while the \c
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smartSpacing() function calculates the spacing between them.
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\section1 FlowLayout Class Implementation
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We start off by looking at the constructor:
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\snippet layouts/flowlayout/flowlayout.cpp 1
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In the constructor we call \c setContentsMargins() to set the left, top,
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right and bottom margin. By default, QLayout uses values provided by
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the current style (see QStyle::PixelMetric).
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\snippet layouts/flowlayout/flowlayout.cpp 2
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In this example we reimplement \c addItem(), which is a pure virtual
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function. When using \c addItem() the ownership of the layout items is
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transferred to the layout, and it is therefore the layout's
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responsibility to delete them.
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\snippet layouts/flowlayout/flowlayout.cpp 3
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\c addItem() is implemented to add items to the layout.
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\snippet layouts/flowlayout/flowlayout.cpp 4
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We implement \c horizontalSpacing() and \c verticalSpacing() to get
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hold of the spacing between the widgets inside the layout. If the value
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is less than or equal to 0, this value will be used. If not,
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\c smartSpacing() will be called to calculate the spacing.
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\snippet layouts/flowlayout/flowlayout.cpp 5
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We then implement \c count() to return the number of items in the
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layout. To navigate the list of items we use \c itemAt() and
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takeAt() to remove and return items from the list. If an item is
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removed, the remaining items will be renumbered. All three
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functions are pure virtual functions from QLayout.
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\snippet layouts/flowlayout/flowlayout.cpp 6
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\c expandingDirections() returns the \l{Qt::Orientation}s in which the
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layout can make use of more space than its \c sizeHint().
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\snippet layouts/flowlayout/flowlayout.cpp 7
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To adjust to widgets of which height is dependent on width, we implement \c
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heightForWidth(). The function \c hasHeightForWidth() is used to test for this
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dependency, and \c heightForWidth() passes the width on to \c doLayout() which
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in turn uses the width as an argument for the layout rect, i.e., the bounds in
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which the items are laid out. This rect does not include the layout margin().
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\snippet layouts/flowlayout/flowlayout.cpp 8
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\c setGeometry() is normally used to do the actual layout, i.e., calculate
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the geometry of the layout's items. In this example, it calls \c doLayout()
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and passes the layout rect.
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\c sizeHint() returns the preferred size of the layout and \c minimumSize()
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returns the minimum size of the layout.
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\snippet layouts/flowlayout/flowlayout.cpp 9
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\c doLayout() handles the layout if \c horizontalSpacing() or \c
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verticalSpacing() don't return the default value. It uses
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\c getContentsMargins() to calculate the area available to the
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layout items.
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\snippet layouts/flowlayout/flowlayout.cpp 10
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It then sets the proper amount of spacing for each widget in the
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layout, based on the current style.
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\snippet layouts/flowlayout/flowlayout.cpp 11
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The position of each item in the layout is then calculated by
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adding the items width and the line height to the initial x and y
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coordinates. This in turn lets us find out whether the next item
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will fit on the current line or if it must be moved down to the next.
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We also find the height of the current line based on the widgets height.
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\snippet layouts/flowlayout/flowlayout.cpp 12
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\c smartSpacing() is designed to get the default spacing for either
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the top-level layouts or the sublayouts. The default spacing for
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top-level layouts, when the parent is a QWidget, will be determined
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by querying the style. The default spacing for sublayouts, when
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the parent is a QLayout, will be determined by querying the spacing
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of the parent layout.
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*/
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