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GUI Programming using NetBeans

GUI Programming using NetBeans. GUI construction. We have previously talked about elements in a (simple) GUI Frames, Panes and Dialogs Text fields Lists and Combo boxes Check and Radio buttons We now look more closely at how to use GUI controls in an application. GUI construction.

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GUI Programming using NetBeans

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  1. GUI Programming using NetBeans

  2. GUI construction • We have previously talked about elements in a (simple) GUI • Frames, Panes and Dialogs • Text fields • Lists and Combo boxes • Check and Radio buttons • We now look more closely at how to use GUI controls in an application RHS – SOC

  3. GUI construction • In general, we have two options when constructing a GUI • Build it ”by hand” using Swing API • Use the NetBeans GUI Builder • Using the GUI Builder is usually much easier than hand-coding the GUI • Does not give you complete control, however… RHS – SOC

  4. GUI construction RHS – SOC

  5. GUI construction • If you wish to construct a GUI manually, you usually begin by creating a JFrame • A JFrame object is essentially an empty window, into which you can add containers for GUI controls • Typically, you will add a JPanel to the frame – the JPanel object will contain the actual GUI controls RHS – SOC

  6. GUI construction public static void main(String[] args) { JFrame theFrame = new JFrame(); theFrame.setBounds(200, 200, 720, 450); theFrame.setVisible(true); JPanel thePanel = new JPanel(); theFrame.add(thePanel); } RHS – SOC

  7. GUI construction • On the JPanel object, various layout strategies can be used • Flow layout – left to right • Border layout – groups into areas • Grid layout – groups into a grid • Border layout is default, and also most commonly used RHS – SOC

  8. GUI construction • Using border layout, the panel is divided into five areas • Center • North • South • East • West RHS – SOC

  9. GUI construction • If a control is put into an area, it will expand to fill out the area • Good when resizing, but may look weird… • If you need a finer level of control, put a panel inside a panel… • …or maybe consider a different layout RHS – SOC

  10. GUI construction public static void main(String[] args) { JFrame theFrame = new JFrame(); theFrame.setBounds(200, 200, 240, 150); theFrame.setVisible(true); JPanel thePanel = new JPanel(); thePanel.setLayout(new BorderLayout()); thePanel.add(new Button("Center"), BorderLayout.CENTER); theFrame.add(thePanel); } RHS – SOC

  11. Exercises • Try out create an application which looks like the picture to the right, without using the GUI Builder. • That is, create it only by using the Swing API methods as shown in the presentation. • Remember that you can put panels within panels… RHS – SOC

  12. Text field • Two common purposes: • Allow the user to enter data as text • Display text data to the user • A text field can be ”enabled” or ”disabled” • Enabled: Data can be entered • Disabled: Data can only be displayed • At some point we need to set or extract the text from the text field RHS – SOC

  13. Text field JFrame theFrame = new JFrame(); theFrame.setBounds(200, 200, 300, 300); JPanel thePanel = new JPanel(); thePanel.setLayout(new BorderLayout()); JTextField theTextField = new JTextField(); thePanel.add(theTextField, BorderLayout.NORTH); theFrame.add(thePanel); theFrame.setVisible(true); RHS – SOC

  14. Text field Text field RHS – SOC

  15. Text field • Enabling a text field theTextField.setEditable(true); • Disabling a text field theTextField.setEditable(false); • Setting the text in a text field theTextField.setText("Greeting earthlings!"); • Getting the text from a text field String s = theTextField.getText(); RHS – SOC

  16. List box / Combo box • A list (or combo) box enables the user to choose an option between many alternatives • List box: User can only choose between specified alternatives • Combo box: User can choose between specified alternatives, or specify choice manually (type it in) RHS – SOC

  17. List box / Combo box Object[] choices = {"One", "Two", "Three", "Four"}; JComboBox theBox = new JComboBox(choices); theBox.setEditable(true); thePanel.add(theBox, BorderLayout.NORTH); RHS – SOC

  18. List box / Combo box Combo box (editable) RHS – SOC

  19. List box / Combo box • Enabling a Combo box theBox.setEditable(true); • Disabling a Combo box theBox.setEditable(false); • Setting the selection in a Combo box theBox.setSelectedItem(”Three"); • Getting the selection from a Combo box String s = (String)theBox.getSelectedItem(); RHS – SOC

  20. Check boxes • In some cases, the set of possible choices is limited to two options • Often a case of either/or, or perhaps on/off • A Check box can only be in two states; checked or unchecked • Nice fit for binary choices RHS – SOC

  21. Check boxes JCheckBox theBBox = new JCheckBox("Bold"); JCheckBox theIBox = new JCheckBox("Italic"); JCheckBox theUBox = new JCheckBox("Underline"); thePanel.add(theBBox,BorderLayout.WEST); thePanel.add(theIBox,BorderLayout.NORTH); thePanel.add(theUBox,BorderLayout.EAST); RHS – SOC

  22. Check boxes RHS – SOC

  23. Check boxes • Enabling a Check box theCBox.setEnabled(true); • Disabling a Check box theCBox.setEnabled(false); • Setting the selection in a Check box theCBox.setSelected(isSelected); • Getting the selection from a Check box boolean isSelected = theCBox.isSelected(); RHS – SOC

  24. Radio buttons • If the number of choices is few, and they are mutually exclusive, use a group of Radio buttons • Only one button in a group of Radio buttons can be selected RHS – SOC

  25. Radio buttons JRadioButton small = new JRadioButton("Small"); JRadioButton medium = new JRadioButton("Medium"); JRadioButton large = new JRadioButton("Large"); ButtonGroup theGroup = new ButtonGroup(); theGroup.add(small); theGroup.add(medium); theGroup.add(large); RHS – SOC

  26. Radio buttons RHS – SOC

  27. Radio buttons • Enabling a Radio button theRB.setEnabled(true); • Disabling a Radio button theRB.setEnabled(false); • Setting the selection in a Radio button theRB.setSelected(isSelected); • Getting the selection from a Radio button boolean isSelected = theRB.isSelected(); RHS – SOC

  28. Radio buttons • Note that even though only one Radio button in a group can be selected, we must call isSelected() until we find it… • Putting Radio buttons in a group does not make them appear grouped visually RHS – SOC

  29. Exercises • Try out create an applica-tion which looks like the picture to the right, without using the GUI Builder. • Only one radio button should be selected at all times • Font for a control can be set using the setFont method (see the docu-mentation) RHS – SOC

  30. The concept of events • On the inside (code), GUI code has a very different structure than ”usual” code • Usual code is driven by con-ditions and various control structures (if, while,…) • GUI code is driven by events RHS – SOC

  31. The concept of events • Execution of GUI code is much more unpredictable than for usual code • We cannot predict – or dictate – what the user does, so we must always handle any possible action the user can do • A user action related to the GUI is called an event RHS – SOC

  32. The concept of events RHS – SOC

  33. The concept of events • Almost all actions the user performs will ”trigger” an event for us to handle • Moving the mouse • Clicking on a button • Writing text in a text box • ….and so on • There are hundreds of possible events! RHS – SOC

  34. The concept of events • Fortunately, is it optional to respond to an event • We only need to do so, if we want any special action to happen • If that is the case, we must write an event handler for that particular event RHS – SOC

  35. Relevant events • Unless we need more sophisticated behavior, we only need to handle two types of events • Choosing a menu item • Clicking on a push button • In both cases, we must create an object which can listen for events from the control in question RHS – SOC

  36. Relevant events • An event listener class must implement a …Listener interface (there are several) • From pushbuttons and menu items, we get ”action events”, so a listener class must implement the ActionListener interface • This interface has a single method: actionPerformed RHS – SOC

  37. Relevant events public class MyListener implements ActionListener { public void actionPerformed(ActionEvent event) { System.out.println("Button clicked"); } } private ActionListener theListener; theListener = new MyListener(); ... JButton theButton = new JButton("Click Me!"); theButton.addActionListener(theListener); RHS – SOC

  38. Relevant events • A very common dialog construction: • Add an ”OK” button • In the event listener for the button • Retrieve data from the relevant controls • Process the data • Close the dialog • Pressing ”OK” means: ”Now my input is ready, do something with it!” RHS – SOC

  39. Wrapping up • GUI programming is somewhat difficult and tedious • Unless you need something special, use the NetBeans GUI Builder! • Always nice to know what does on under the hood… • You can – to some degree – mix manual coding and using the GUI Builder RHS – SOC

  40. Exercises • Try out create an application which looks like the picture to the right, without using the GUI Builder. • Create event listeners for the buttons, that print the texts: • ”Brrr” for Arctic and Antarctic • ”Puhh” for America and Asia • ”Wet!” for Atlantic • You should not write more than three event listeners! RHS – SOC

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