Understanding Layouts in SWT

1. Understanding Layouts in SWT

2. Summary • When writing applications in SWT, you may need to use layouts to give your windows a specific look. • A layout controls the position and size of children in a Composite. • Layout classes are subclasses of the abstract class Layout. • How to work with standard layouts, and • How to writeyour own custom layout class.

3. Overview • Positioning and sizing widgets in a parent control does not happen automatically. • Two approaches: • size and place a Composite’s children initially, or in a resize listener. • specify a layout class to position and size the children. • Note:If children are not given a size, they will have zero size and they cannot be seen.

4. Basic Layout Terminology in SWT

5. Basic Layout Terminology in SWT • Composite (in this case, a TabFolder) has a location(x,y), clientArea(x,y, width, height) andtrim. • The size of the Composite is the size of the clientArea plus the size of thetrim. • This Composite has two children that are laid out side by side. • A Layoutis managing the size and position of the children. • This Layout allowsspacing between the children, and a margin between the children and the edges of the Layout. • The size of the Layout is the same as the size of the Composite’s clientArea.

6. Preferred Size of a widget • The preferred size of a widget is the minimum size needed to show its content. • For Composite, the preferred size is the smallest rectangle that contains all of its children. • if children positioned by the application, the Composite computes its own preferred size based on the size and position of the children. • If a Composite is using a layout class to position its children, it asks the Layout to compute the size of its clientArea, and then it adds the trims to determine its preferred size.

7. Standard Layouts • FillLayout • lays out equal-sized widgets in a single row or column • RowLayout • lays out widgets in a row/colum or rows/columns, with fill, wrap, and spacing options • GridLayout • lays out widgets in a grid of a fixed number of columns. • FormLayout • lays out widgets by creating attachments for each of their sides • In package org.eclipse.swt.layout • All subcalsses of abstract class Layout

8. Associate a layout to controls • usesetLayout(Layout) • Shell shell = new Shell(); • shell.setLayout(new RowLayout()); • Layout data • contains layout data for a specific child. • Called layout data class • if {A}Layout is a layout class •  {A}Data its layout data class name. • A widget’s layout data class is set as follows: • Button button =new Button(shell, SWT.PUSH); • button.setLayoutData(new RowData(50, 40));

9. Examples import org.eclipse.swt.*; import org.eclipse.swt.widgets.*; import org.eclipse.swt.layout.*;  publicclass LayoutExample {  publicstaticvoid main(String[] args) { // main thread is the UI thread Display display = new Display(); Shell shell = new Shell(display); // Create the layout. RowLayout layout = new RowLayout(); // Optionally set layout fields. layout.wrap = true; // Set the layout into the composite. shell.setLayout(layout); // Create the children of the composite.

10. new Button(shell, SWT.PUSH) .setText("B1"); new Button(shell, SWT.PUSH) .setText("Wide Button 2"); new Button(shell,SWT.PUSH) .setText("Button 3"); shell.pack(); shell.open(); while (!shell.isDisposed()) { if (!display.readAndDispatch()) display.sleep(); } }

11. Results • Running the above code results in the following: • If resizes s.t. no room for Button 3 on the right • =>the RowLayout wraps Button 3 to the next row, as follows:

12. FillLayout • the simplest layout class. • lay out widgets in a single row or column, forcing them to have the same width and height. • All widgets will share the allocated space except those for margins and spacing. • FillLayoutdoes not wrap, but you can specify margins and spacing (default = 0). • lay out buttons in a task bar or tool bar, • stack checkboxes in a Group. • Single child Composite. • Ex: if a Shell has a single Group child, FillLayout will cause the Group to completely fill the Shell. • no layout data for child elements

13. Example FillLayout fillLayout = new FillLayout(); fillLayout.type = SWT.VERTICAL;    shell.setLayout(fillLayout);    new Button(shell, SWT.PUSH).setText("B1"); new Button(shell, SWT.PUSH).setText("Wide Button 2"); new Button(shell, SWT.PUSH).setText("Button 3");

14. Margin and Spacing • marginWidth, marginHeight, and spacing • These fields control the number of pixels between widgets (spacing) and the number of pixels between a widget and the side of the parent Composite (marginWidth and marginHeight). • By default, All values are 0. marginHeight marginWidth marginWidth marginHeight

15. Results

16. FillLayout Summary

17. RowLayout • more commonly used than FillLayout • can wrap, • configurable margins and spacing. • has a number of configuration fields. • the height and width of each widget in a RowLayout can be specified by setting the widget’s RowData object using setLayoutData.

19. RowLayout Configuration Fields • type [=SWT.HORIZONTAL] // 水平/垂直分布 • controls whether the contained widgets are layouted in horizontal rows, or vertical columns. • Wrap [=true] ; // 捲折 • controls whether the row of widgets may be wrapped into the next row if there isn’t enough space. • Pack [=true]// 相同/不等 寬高 • If true, widgets take their preferred size(from RowData or computeSize() ), and be aligned to the left. • If false, all widgets will get an equal size (for width as well as height), which is the maximum of the preferred sizes of all children; somewhat different from FillLayout.

20. justify [=false]// 額外空白 由連接區均分 / 置於後端 • true  extra space than needed distributed evenly among margins/spacings b/t widgets. • false  extra space left at the right/bottom end. • Note: While pack and fill will affect the size of child widgets, justify does not.

21. The fill field in a RowLayout • fill [= false] // 同列(欄)是否等高(寬) • Indicates whether all controls in a row (or column) will have the same height (or width). • same height (or width) => select the largest control in the row( or column). • fill=false • for controls in a row with different height  Even on top and ragged on bottom. (top aligned ) • for controls in a column with different width  Even on left and ragged on right. (left aligned ) • fill = true  even on both sides.

22. Margin and Spacing • marginHeigth, marginWidth, spacing: • same as FillLayout • marginLeft, marginTop, marginRight, marginBottom • These fields specify additional number of pixels between a widget and the side of the parent Composite (margin). • By default, RowLayouts leave 3 pixels for margins and spacing.

23. RowLayout Examples • RowLayout rowLayout = new RowLayout(); • rowLayout.wrap = false;   rowLayout.pack = false; • rowLayout.justify = true; • rowLayout.type = SWT.VERTICAL; • rowLayout.marginLeft = 5;   rowLayout.marginTop = 5; • rowLayout.marginRight = 5;  rowLayout.marginBottom = 5; • rowLayout.spacing = 0; • shell.setLayout(rowLayout); • If Using default layout => only line 1. Is needed.

24. Results

26. Using RowData Objects with RowLayout publicclass RowDataExample {  publicstaticvoid main(String[] args) {        Display display = new Display();        Shell shell = new Shell(display);        shell.setLayout(new RowLayout());        Button button1 = new Button(shell, SWT.PUSH);        button1.setText("Button 1");        button1.setLayoutData(new RowData(50, 40));        Button button2 = new Button(shell, SWT.PUSH);        button2.setText("Button 2");        button2.setLayoutData(new RowData(50, 30));

27. Button button3 = new Button(shell, SWT.PUSH);     button3.setText("Button 3");     button3.setLayoutData(new RowData(50, 20));     shell.pack();     shell.open(); while (!shell.isDisposed()) { if (!display.readAndDispatch()) display.sleep();        }    }}

28. GridLayout • the most useful and popularly used • the widget children of a Composite are laid out in a grid. • has a number of configuration fields, • Each widget can have an associated layout data, called GridData. • The power of GridLayout lies in the ability to configure GridData for each widget .

30. GridLayout Configuration Fields • numColumns [=1] • Number of columns in a row • If #widgets > numColumns => wrap into next rows.

31. Example Display display = new Display(); Shell shell = new Shell(display); GridLayout gridLayout = new GridLayout(); gridLayout.numColumns = 3; shell.setLayout(gridLayout); new Button(shell, SWT.PUSH).setText("B1"); new Button(shell, SWT.PUSH).setText("Wide Button 2"); new Button(shell, SWT.PUSH).setText("Button 3"); new Button(shell, SWT.PUSH).setText("B4"); new Button(shell, SWT.PUSH).setText("Button 5"); shell.pack();   shell.open(); while (!shell.isDisposed()) { if (!display.readAndDispatch()) display.sleep();   }

33. makeColumnsEqualWidth [=false] • forces all columns to be the same width. • (note that in the absence of further instruction, widgets are left-justified in their columns). • by default the width of a column is the width of the widest widget in the column.

34. margins • marginWidth, marginHeight, horizontalSpacing, andverticalSpacing • similar to those in a RowLayout. • left and right margins are grouped into marginWidth, • the top and bottom margins are grouped into marginHeight. • can specify horizontalSpacing and verticalSpacing independently, • whereas in a RowLayout, spacing applies to horizontal or vertical depending on the type of the RowLayout.

35. GridData Object Fields • GridData • the layout data object associated with GridLayout. • use setLayoutData method to set a widget’s GridData object. • note: Do not share GridData: each widget must have its own GridData. • Example: Button button1 = new Button(shell, SWT.PUSH);    button1.setText("B1"); // all gridData fields are set to default values    button1.setLayoutData(new GridData());

36. How to set GridData Fields 1. Set the fields directly, like this:  GridData gridData = new GridData(); gridData.horizontalAlignment = GridData.FILL; gridData.grabExcessHorizontalSpace = true; button1.setLayoutData(gridData);  2. Use style bits defined in GridData: button1.setLayoutData( new GridData( GridData.HORIZONTAL_ALIGN_FILL | GridData.GRAB_HORIZONTAL));// or further button1.setLayoutData(new GridData( GridData.FILL_HORIZONTAL));

37. HorizontalAlignment and VerticalAlignment • The alignment fields specify where to place a widget horizontally and/or vertically within its grid cell. • Each alignment field can have one of the following values: • BEGINNING [置左/置上] • CENTER [置中] • END [置右/置下] • FILL [佈滿空格] • defined in both SWT and GridData classes. • Default values: • horizontalAlignment ==>BEGINNING (or left-aligned). • verticalAlignment ==>CENTER.

38. Example: vary the horizontalAlignment of Button 5.

39. HorizontalIndent • Allows you to move a widget to the right by a specified number of pixels. • useful only when the horizontalAlignment is BEGINNING. • Ex: GridData gridData = new GridData(); gridData.horizontalIndent = 4; button5.setLayoutData(gridData); horizontalIdent

40. HorizontalSpan and VerticalSpan • The span fields let widgets occupy more than one grid cells. • often used in conjunction with FILL alignment. • Example: make Button 5 span the last two cells: GridData gridData = new GridData(); gridData.horizontalAlignment = GridData.FILL; gridData.horizontalSpan = 2; button5.setLayoutData(gridData);

41. More Examlpes • make Wide Button 2 span two cells instead:   GridData gridData = new GridData(); gridData.horizontalAlignment = GridData.FILL; gridData.horizontalSpan = 2; button2.setLayoutData(gridData); • make Button 3 span two cells vertically: GridData gridData = new GridData(); gridData.verticalAlignment = GridData.FILL; gridData.verticalSpan = 2; button3.setLayoutData(gridData);

42. GrabExcessHorizontalSpace and GrabExcessVerticalSpace • typically used for larger widgets such as Text,List or Canvasto allow them to grow if their containing Composite grows. • If a Text is grabbing excess horizontal space and the user resizes the Shell wider, then the Text will get all of the new horizontal space and other widgets in the same row will stay their original width. • Of course, the widget that is grabbing excess space is also the first one to shrink when the Shell gets smaller. • It is easiest to always think of the grabExcessSpace fields in the context of resizing.

43. Example • original :  after resizing • new GridData: • B3: grab excess horizontal and • vertical space, • B1,B4:fill vertically ( w/o • grabbing)

44. The code Button button1 = new Button(shell, SWT.PUSH);    button1.setText("B1");    GridData gridData = new GridData();    gridData.verticalAlignment = GridData.FILL;    button1.setLayoutData(gridData); new Button(shell, SWT.PUSH).setText("Wide Button 2");    Button button3 = new Button(shell, SWT.PUSH);    button3.setText("Button 3");    gridData = new GridData();    gridData.verticalAlignment = GridData.FILL; gridData.verticalSpan = 2; gridData.grabExcessVerticalSpace = true; gridData.horizontalAlignment = GridData.FILL; gridData.grabExcessHorizontalSpace = true;    button3.setLayoutData(gridData);

45. Button button4 = new Button(shell, SWT.PUSH);    button4.setText("B4");    gridData = new GridData(); gridData.verticalAlignment = GridData.FILL;    button4.setLayoutData(gridData); new Button(shell, SWT.PUSH).setText("Button 5");

46. If more than one widget is trying to grab the same space, then the excess space is shared evenly among the grabbing widgets: •  original resize:

47. Final Notes • If a widget is grabbing excess horizontal/vertical space and its parent Composite grows wider/taller • then the entire column/row containing that widget grows wider/taller. • Implications: • if any other widget in the affected column or row has fill alignment, then it will stretch also. • Widgets that have beginning, center, or end alignment will not stretch – they will stay at the beginning, center or end of the wider column or taller row.

48. WidthHint and HeightHint • Indicate the number of pixels wide or tall that you would like a widget to be, if it does not conflict with other requirements in the GridLayout’s constraint system. • Example: • Looking back at the five-button, three-column example, say we want Button 5 to be 70 pixels wide and 40 pixels tall. • We code it as follows: • GridData gridData = new GridData(); •        gridData.widthHint = 70; •        gridData.heightHint = 40; •        button5.setLayoutData(gridData);

49. public fields of GridData • verticalAlignment, horizontalAssignment : • Specifies the vertical (horizontal) alignment of the control within a cell. • can be one of SWT.BEGINNING (or SWT.TOP, SWT.LEFT), SWT.END (or SWT.BOTTOM,SWT.RIGHT), SWT.CENTER, or SWT.FILL. • widthHint, heightHint : • The amount of space in pixels to be used as the width hint for the control. • The default value is SWT.DEFAULT. • horizontalIndent [1] • specifies the number of pixels of indentation to be placed on the left side of the cell. • horizontalSpan, verticalSpan : [1] • Specifies the number of columns (rows) that the cell will fill. • grabExcessHorizontal, grabExcessVerticalSpace : [false] • Indicates that this cell will accept any excess vertical space that remains after each cell has been placed. If more than one instance of GridData wants excess space, it is divided evenly among them.