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 RHS – SOC

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

GUI construction RHS – SOC

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

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

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

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

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

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

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

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

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

Text field Text field RHS – SOC

Text field Enabling a text field Disabling 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

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

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

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

List box / Combo box Enabling a Combo box Disabling 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

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

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

Check boxes RHS – SOC

Check boxes Enabling a Check box Disabling 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

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

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

Radio buttons RHS – SOC

Radio buttons Enabling a Radio button Disabling 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

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

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

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

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

The concept of events RHS – SOC

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

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

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

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

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

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

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

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