Layout Management

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                  Qt provides several classes that lay out widgets on a form: QHBoxLayout, QVBoxLayout, QGridLayout, and QStackLayout.Other classes that perform layout management include QSplitter,QScrollArea,QMainWindow,and QWorkSpace.  A widget's size policy tells the layout system how it should stretch or shrink. Qt provides sensible default size policies for all its built-in widgets,but since no single default can account for every possible layout,it is still common for developers to change the size policies for one or two widgets on a form.A QSizePolicy has both a horizontal and a Vertical component.Here are the most useful values:  (1) Fixed  means that the widget cannot grow or shrink.The widget always stays      at the size of its size hint.  (2) Minimum  means that the widget's size hint is its minimum size.The widget       cannot shrink below the size hint,but it can grow to fill available space       if necessary.  (3) Maximum  means that the widget's size hint is its maximum size.The widget      can be shrunk down to its minimum size hint.  (4) Preferred  means that the widget's size hint is its preferred size,but that      the widget can still shrink or grow if necessary.  (5) Expanding  means that the widget can shrink or grow and it is especially       willing to grow.  (6) Ignore is similar to Expanding,except that it ignores the widget's size       hint and minimum size hint.   The difference between Preferred and Expanding is that when a form that containsboth Preferred and Expanding widgets is resized,extra space is given to the Expandingwidgets,while the Preferred widgets stay at their size hint.   In addition to the size policy's horizontal and vertical components,the QSizePolicy class stores a horizontal and a vertical stretch factor.These stretch factors can be used to indicate that different child widgets should grow at different rates when the form expands.   Yet another way of influcening a layout is to set a minimum size,a maximum size,or a fixed size on the child widgets.  Splitters  A Qsplitter is a widget that contains other widgets.The widgets in a splitter areseperated by splitter handles.Users can change the sizes of a splitter's child widgets by dragging the handles.Splitters can often be used as an alternative to layout managers,to give more control to the user.For example:int main(int argc,char *argv[])
{
  QApplication app(argc,argv);  QTextEdit *editor1 = new QTextEdit;  QTextEdit *editor2 = new QTextEdit;  QTextEdit *editor3 = new QTextEdit;  QSplitter splitter(Qt::Horizontal);  splitter.addWidget(editor1);  splitter.addWidget(editor2);  splitter.addWidget(editor3);  
...  splitter.show(); 
return app.exec();
}
               
               
               

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