Documented the flow layout example.

Wrote documentation for the flowlayout class.

Task-number: 252548
Rev-by: Geir Vattekar
Rev-by: janarve

2 files changed, 113 insertions, 4 deletions

diff --git a/doc/src/examples/flowlayout.qdoc b/doc/src/examples/flowlayout.qdoc
index 557ba39..5fdafe2 100644
--- a/doc/src/examples/flowlayout.qdoc
+++ b/doc/src/examples/flowlayout.qdoc
@@ -43,8 +43,117 @@
     \example layouts/flowlayout
     \title Flow Layout Example
 
-    The Flow Layout example demonstrates a custom layout that arranges child widgets from
-    left to right and top to bottom in a top-level widget.
+    The Flow Layout example demonstrates a custom layout that arranges child 
+    widgets from left to right and top to bottom in a top-level widget.
 
-    \image flowlayout-example.png
-*/
+    \image flowlayout-example.png Screenshot of the Flow Layout example
+
+    The items are first laid out horizontally and then vertically when each line
+    in the layout runs out of space. 
+
+	The Flowlayout class mainly uses QLayout and QWidgetItem, while the
+	Window uses QWidget and QLabel. We will only document the definition 
+	and implementation of \cFlowLayout below.
+
+    \section1 FlowLayout Class Definition
+    
+    The \c FlowLayout class inherits QLayout. It is a custom layout class 
+    that arranges its child widgets horizontally and vertically. 
+
+    \snippet examples/layouts/flowlayout/flowlayout.h 0
+
+    We reimplement functions inherited from QLayout. These functions add items to
+    the layout and handle their orientation and geometry. 
+    
+    We also declare two private methods, \c doLayout() and \c smartSpacing().
+    \c doLayout() lays out the layout items, while the \c
+    smartSpacing() function calculates the spacing between them.
+
+    \section1 FlowLayout Class Implementation 
+
+    We start off by looking at the constructor:
+
+    \snippet examples/layouts/flowlayout/flowlayout.cpp 1
+
+    In the constructor we call \c setContentsMargins() to set the left, top,
+    right and bottom margin. By default, QLayout uses values provided by
+    the current style (see QStyle::PixelMetric). 
+
+    \snippet examples/layouts/flowlayout/flowlayout.cpp 2
+
+    In this example we reimplement \c addItem(), which is a pure virtual 
+    function. When using \c addItem() the ownership of the layout items is 
+    transferred to the layout, and it is therefore the layout's 
+    responsibility to delete them. 
+    
+    \snippet examples/layouts/flowlayout/flowlayout.cpp 3
+    
+    \c addItem() is implemented to add items to the layout. 
+
+    \snippet examples/layouts/flowlayout/flowlayout.cpp 4
+
+    We implement \c horizontalSpacing() and \c verticalSpacing() to get
+    hold of the spacing between the widgets inside the layout. If the value 
+    is less than or equal to 0, this value will be used. If not, 
+    \c smartSpacing() will be called to calculate the spacing.
+
+    \snippet examples/layouts/flowlayout/flowlayout.cpp 5
+    
+    We then implement \c count() to return the number of items in the 
+    layout. To navigate the list of items we use \c itemAt() and 
+    takeAt() to remove and return items from the list. If an item is 
+    removed, the remaining items will be renumbered. All three 
+    functions are pure virtual functions from QLayout.
+
+    \snippet examples/layouts/flowlayout/flowlayout.cpp 6
+
+    \c expandingDirections() returns the \l{Qt::Orientation}s in which the
+    layout can make use of more space than its \c sizeHint().
+
+    \snippet examples/layouts/flowlayout/flowlayout.cpp 7
+
+    To adjust to widgets of which height is dependent on width, we implement \c
+    heightForWidth(). The function \c hasHeightForWidth() is used to test for this
+    dependency, and \c heightForWidth() passes the width on to \c doLayout() which
+    in turn uses the width as an argument for the layout rect, i.e., the bounds in
+    which the items are laid out. This rect does not include the layout margin().
+    
+    \snippet examples/layouts/flowlayout/flowlayout.cpp 8
+
+    \c setGeometry() is normally used to do the actual layout, i.e., calculate
+    the geometry of the layout's items. In this example, it calls \c doLayout()
+    and passes the layout rect.
+
+    \c sizeHint() returns the preferred size of the layout and \c minimumSize()
+    returns the minimum size of the layout.
+
+    \snippet examples/layouts/flowlayout/flowlayout.cpp 9
+
+    \c doLayout() handles the layout if \c horizontalSpacing() or \c
+    verticalSpacing() don't return the default value. It uses 
+    \c getContentsMargins() to calculate the area available to the 
+    layout items. 
+ 
+    \snippet examples/layouts/flowlayout/flowlayout.cpp 10
+
+	It then sets the proper amount of spacing for each widget in the 
+	layout, based on the current style. 
+	
+    \snippet examples/layouts/flowlayout/flowlayout.cpp 11
+
+	The position of each item in the layout is then calculated by 
+	adding the items width and the line height to the initial x and y 
+	coordinates. This in turn lets us find out whether the next item 
+	will fit on the current line or if it must be moved down to the next. 
+	We also find the height of the current line based on the widgets height. 
+	
+    \snippet examples/layouts/flowlayout/flowlayout.cpp 12
+
+	\c smartSpacing() is designed to get the default spacing for either 
+	the top-level layouts or the sublayouts. The default spacing for 
+	top-level layouts, when the parent is a QWidget, will be determined 
+	by querying the style. The default spacing for sublayouts, when 
+	the parent is a QLayout, will be determined by querying the spacing 
+	of the parent layout.
+
+*/
\ No newline at end of file
diff --git a/doc/src/images/flowlayout-example.png b/doc/src/images/flowlayout-example.png
index 27660d6..61abe1f 100644
--- a/doc/src/images/flowlayout-example.png
+++ b/doc/src/images/flowlayout-example.png