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Layout managementand event handling

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  • 1. Ch 20 Layout Management and Event Handling
  • 2. Layout Managers  Removes repetitious need to lay out components precisely.  Insulates developer from the fact that components have different sizes when instantiated on different platforms.  All implement java.awt.LayoutManager interface.
  • 3. Layout of Components  FlowLayout  left to right & top down  BorderLayout  north, south, west, east & center  CardLayout  stack of panels  GridLayout  tabular form (rows & columns)  GridBagLayout  tabular form(variable row heights and column widths)
  • 4. Component Size and Position  Sizes and positions are merely suggestions, overridden by the LayoutManager.  Each Component has a preferred size, which is “just big enough” to display the component.
  • 5. Use Layout Managers  Default layout managers  Windows (Frames & Dialogs)  BorderLayout  Panels & Applets  FlowLayout setLayout(new FlowLayout()); setLayout(new BorderLayout()); setLayout(new CardLayout(()); setLayout(new GridLayout(rows,columns,xgap,ygap));
  • 6.  FlowLayout  The flow layout is the default layout manager for all Panel objects and applets.  It simply lays out components in a single row, from left to right starting a new row if its container is not sufficiently wide .  Default alignment is CENTER.  new FlowLayout() // default is centered with 5 pixel gaps  new FlowLayout(int align)  new FlowLayout(int align, int hgap, int vgap)
  • 7. GridLayout  GridLayout lays out components in a rectangular grid, where all cells are equal size.  Components are addes cell by cell left to right ,filling top row and then moving down  GridLayout() default of one column per component, in a single row.  GridLayout(int rows, int cols) Creates a grid layout with the specified number of rows and columns.  GridLayout(int rows, int cols, int hgap, int vgap) Creates a grid layout with the specified number of rows and columns.  e.g setLayout(new GridLayout(3,5,10,15));
  • 8. BorderLayout  Divides the container into five regions: east, south, west, north, and center.  Takes maximum 5 components only, one per region.  Resizes each component to match the size of its region.  Resizes each region when the container is resized.
  • 9. BorderLayout Manager “Center” “North” “South” “West” “East”
  • 10.  While adding a component a region is specified as an argument to add() as BorderLayout.NORTH  e.g add(new Button(“OK”),BorderLayout.SOUTH);
  • 11. GridBagLayout  GridBagLayout is a flexible layout manager that aligns components vertically and horizontally, without requiring that the components be the same size .  GridBagLayout (int gridx , int gridy, int gridwidth ,int gridheight ,int weightx, double weighty double anchor, int fill ,int insets , int ipadx int ipady )
  • 12.  gridx,gridy : define col ,and row position of upper left corner.  gridwidth ,gridheight : no of cells occupied by components .default is 1 for both  weightx,weighty: Specifies how to distribute extra horizontal space  anchor:It determines where, within the display area, to place the component.  fill:This field is used when the component's display area is larger than the component's requested size.  Insets:This field specifies the external padding of the component, the minimum amount of space between the component and the edges of its display area.  Ipadx, ipady:This field specifies the internal padding
  • 13.  CardLayout:The CardLayout class lets you implement an area that contains different components at different times .  CardLayout() Creates a new card layout with gaps of size zero .  CardLayout(int hgap, int vgap) Creates a new card layout with the specified horizontal and vertical gaps.