CS3006N Week 9 more GUI Programming

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CS3006N Week 9more GUI Programming

• James King

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Warning

• Do not look at this week until you have
  understood last weeks lecture
• This week will continue with the example from
  last week so grab the final code from last weeks
  lecture I.e. the frame

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The List

• Lists allow you to select from a fixed choice of
  items.
• llnew List()
• ll.setBounds(10,100,100,100)
• ll.add("choice 1")
• ll.add("choice 2")
• ll.add("choice 3")
• f.add(ll)

X, Y, (within frame) width, Height
Add the possible choices to the list
Add list to the frame
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The List

• You can find out the text at any position in the
  list using getItem(position)
• You can find out how man items are in the list
  using getItemCount()
• You can find out which item is selected using
  getSelectedIndex() which returns the position of
  the selected item
• or
• getSelectedItem() which returns the text of the
  selected item

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The List

• You can force an entry to be selected by using
  select(position) or select(item text)
• You can delete an entry using remove(position) or
  remove(item text)
• You can delete all the items using removeAll()

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The List

• Like all the GUI components examined last week
  lists have
• setVisible(true or false)
• setEnabled(true or false)

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List Events

• Lists can generate many events
• ActionPerformed if an item is double clicked on
• itemStateChanged if an item is selected or
  deselected
• To handle ActionPerformed events requires your
  class to implement an ActionListener
• To handle itemStateChanged events requires your
  class implements an ItemListener

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ActionListener

• public class main implements ActionListener
• public void actionPerformed(ActionEvent e)
• if (e.getSource()ll)
• l.setText( ouch )
• ll.addActionListener(this)

Handle the button press
Change the label to say ouch!
This code is added to the main method to attach
the action listener to the List
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ItemListener
public class main implements ItemListener publ
ic void itemStateChanged(ItemEvent e)
if (e.getStateChange()e.SELECTED )
l.setText("Selected
"e.getItem())
if (e.getStateChange()e.DESELECTED )

l.setText("DESelected"e.getItem())
ll.addItemListener(this)

Handle item is selected
Handle item is deselected
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Choice

• Choice is related to List in that it displays a
  set of possible options and generates
  itemStateChanged events
• Adding items, getting the selected items etc are
  the same as List
• Choice does not generate
• ActionPerformed events

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Choice

• cnew Choice()
• c.setBounds(10,100,100,100)
• c.add("choice 1")
• c.add("choice 2")
• c.add("choice 3")
• c.addItemListener(this)
• f.add(c)

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Choice

• Since both List and Choice generate
  itemStateChanged events inside the
  itemStateChaged method you will need to check who
  originated the event.
• public void itemStateChanged(ItemEvent e)
• if (e.getSource()c)
• if (e.getStateChange()e.SELECTED )
  
• l.setText("Selected
  "e.getItem())
• if (e.getStateChange()e.DESELECTED
  )
• l.setText("DESelected
  "e.getItem())

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Checkbox

• A checkbox asks a simple yes or no question
• cbnew Checkbox()
• cb.setBounds(10,100,100,100)
• cb.setLabel("Pass IM257?")
• cb.addItemListener(this)
• It can also generate an
• itemStateChanged event

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Checkbox

• You can set the checkbox to on or off using
  setState(true or false)
• You can find out of the checkbox is on or off
  using getState()
• Checkbox supports getLabel(), setLabel(new
  label), setVisible(true or false) and
  setEnabled(true or false)

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CheckboxGroup

• The CheckboxGroup only allows one of the grouped
  checkboxes to be on at any one time
• cgnew CheckboxGroup()
• cb1new Checkbox("Fail IM257",cg,false)
• cb1.setBounds(10,100,100,20)
• cb2new Checkbox("Pass IM257",cg,false)
• cb2.setBounds(10,120,100,20)
• cb3new Checkbox("Avoid IM257",cg,false)
• cb3.setBounds(10,140,100,20)
• f.add(l)
• f.add(cb1)
• f.add(cb2)
• f.add(cb3)

Construct the manager
Manager becomes a parameter to the constructor
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CheckboxGroup

• You can find out the selected checkbox by using
  getSelectedCheckbox()
• You can set the selected checkbox using
  setSelectedCheckbox(index)

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CheckboxGroup

• CheckboxGroup has not events of its own so you
  will still need to attach listeners to the
  individual Checkboxes
• CheckboxGroup does not have
• setVisible(true or false)
• setEnabled(true or false)
• Again you need to talk to the individual
  Checkboxes

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Color without a u!

• All the components we have examined have methods
  to set the background and foreground colours
  using setBackground(Color) and setForeground(Color
  )
• The Color object allows various ways of
  specifying a colour
• There are a set of predefined colours Color.blue
  etc
• You can specify the RGB values for the colour
• Color cnew Color(10,10,10)

Red, green,blue
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Further Reading

• Look at www.java.sun.com
• Look for the Java tutorial and look at AWT
  programming
• Look for the online documentation for the
  java.awt package