Suppose I have a Java application that has more than one component in which you can enter text. Now suppose this application also has a dialog that lets you insert a single character (like the dialog in Word that comes up when you select Insert from the Edit menu) into those components. You want it to insert the character into whichever text component last had the focus.
But how do you know which text component last had the focus?
I could keep track of this manually, by having each text component report to the application whenever it gets the focus and then have the application insert the new character into whichever component that last had the focus.
But this must be a common problem (consider Paste buttons in tool bars---how does it know where to paste it into?). Is there something already built in to Swing that lets you get a handle to the last text component that had the focus? Or do I need to write this myself?
Is there something already built in to Swing that lets you get a handle to the last text component that had the focus?
You create an Action that extends TextAction. The TextAction class has a method that allows you to obtain the last text component that had focus.
Edit:
You can create your own Action and do whatever you want. The Action can then be added to any JMenuItem or JButton. For example:
class SelectAll extends TextAction
{
public SelectAll()
{
super("Select All");
}
public void actionPerformed(ActionEvent e)
{
JTextComponent component = getFocusedComponent();
component.selectAll();
}
}
If you just want to insert a character at the caret position of the text field then you can probably just do
component.replaceSelection(...);
Edit 2:
I don't understand what the confusion is with this answer. Here is a simple example:
select some text
use the mouse to click on the check box
tab or use the mouse to click on the "Cut" button
It doesn't matter that the text field doesn't currently have focus when the Action is invoked. The TextAction tracks the last text component that had focus.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;
public class TextActionTest extends JFrame
{
JTextField textField = new JTextField("Select Me");
JTabbedPane tabbedPane;
public TextActionTest()
{
add(textField, BorderLayout.NORTH);
add(new JCheckBox("Click Me!"));
add(new JButton(new CutAction()), BorderLayout.SOUTH);
}
public static void main(String[] args)
{
TextActionTest frame = new TextActionTest();
frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
frame.pack();
frame.setLocationRelativeTo( null );
frame.setVisible(true);
}
class CutAction extends TextAction
{
public CutAction()
{
super("Click to Cut Text");
}
public void actionPerformed(ActionEvent e)
{
JTextComponent component = getFocusedComponent();
// JTextComponent component = getTextComponent(e);
component.cut();
}
}
}
Just like suggested by #lesmana (+1 for that).
Here you have an example that shows that on focusLost the focus listener returns the previously focused component.
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class Focusing
{
public static void main(String[] args)
{
JPanel p = new JPanel();
JTextField tf1 = new JTextField(6);
tf1.setName("tf1");
p.add(tf1);
JTextField tf2 = new JTextField(6);
tf2.setName("tf2");
p.add(tf2);
FocusListener fl = new FocusListener()
{
#Override
public void focusGained(FocusEvent e)
{
System.out.println("focusGained e.getSource().c=" + ((JComponent) e.getSource()).getName());
}
#Override
public void focusLost(FocusEvent e)
{
System.out.println("focusLost e.getSource().c=" + ((JComponent) e.getSource()).getName());
}
};
tf1.addFocusListener(fl);
tf2.addFocusListener(fl);
JPanel contentPane = new JPanel();
contentPane.add(p);
JFrame f = new JFrame();
f.setContentPane(contentPane);
f.setSize(800, 600);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setVisible(true);
}
}
All the best, Boro.
I've never done this directly, but you could look into the FocusEvents and the Focus Subsystem.
Hopefully there is something in the Focus Subsystem that would fire events that you could listen for.
You can register a FocusListener to every text component. The FocusEvent object has a reference to the last component which had focus.
Related
I am a fairly new user with programming in Java with about a week and a bit experience, as of before I have been using python for about 3 years but thought to give java a try.
I have been trying to develop my skills by creating small projects and applications and am now creating a small GUI counter.
I have achieved creating the GUI with 2 buttons and a label and have tested the maths behind the application but I am struggling to work out how the ActionListener works as it feels a lot different to python when making a button have a action.
This is My Code;
package gui;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.*;
public class GUI{
//This creates a frame or panel to contain things
public static void main(String[] args) {
//Maths To The Counter
int Counter = 0;
System.out.println(Counter);
Counter =+ 1;
System.out.println(Counter);
//Creating The Frame
JFrame frame = new JFrame();
JPanel panel = new JPanel();
panel.setBackground(Color.WHITE);
frame.getContentPane().add(panel);
//Creating The Label
JLabel label3 = new JLabel("Counter: ");
panel.add(label3);
//Button Which should have a funtion to add and display the number
JButton button = new JButton("Click Here.");
panel.add(button);
//Button to reset the counter
JButton buttonReset = new JButton("Reset Counter.");
panel.add(buttonReset);
//Set Size Of Window
frame.setSize(new Dimension(500, 400));
//Set Starting Position to centre
frame.setLocationRelativeTo(null);
//Setting a default close action
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Set Title
frame.setTitle("Counter");
//Disable Resize
frame.setResizable(false);
//Setting if its visible
frame.setVisible(true);
//Fits frame to fit everything
frame.pack();
}
}
enter code here
I know that in python a action is in a function so that has been my logic to this problem however I have seen that I need to use the actionlistener instead and I am struggling to get my head around it.
If Someone could show me how this type of action should be implemented it would be great help, I have watch some youtube videos and done a bit of research but im still struggling to understand in my situation how to do it.
For any confussion im sorry, overall my question is how do I add a action to a button in my program that can implement my maths at the start.
As well any feedback on the structure of my code would be welcomed as I am just starting in java and I do know poor structure can lead to mistakes.
This code should work:
Basically, in the main method I am creating an instance of the class and calling a method to create the gui.
I also created an instance variable as the counter, otherwise you won't be able to update the variable in your action listener.
public class Gui {
private int counter;
// This creates a frame or panel to contain things
public static void main(String[] args) {
Gui gui = new Gui();
gui.create();
}
private void create() {
// Creating The Frame
JFrame frame = new JFrame();
JPanel panel = new JPanel();
panel.setBackground(Color.WHITE);
frame.getContentPane().add(panel);
// Creating The Label
JLabel label3 = new JLabel("Counter: ");
panel.add(label3);
// Button Which should have a funtion to add and display the number
JButton button = new JButton("Click Here.");
panel.add(button);
button.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
System.out.println(counter++);
}
});
// Button to reset the counter
JButton buttonReset = new JButton("Reset Counter.");
panel.add(buttonReset);
buttonReset.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
counter = 0;
}
});
// Set Size Of Window
frame.setSize(new Dimension(500, 400));
// Set Starting Position to centre
frame.setLocationRelativeTo(null);
// Setting a default close action
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Set Title
frame.setTitle("Counter");
// Disable Resize
frame.setResizable(false);
// Setting if its visible
frame.setVisible(true);
// Fits frame to fit everything
}
}
With Lambda expressions, you can simplify your action listeners as follows:
button.addActionListener(a -> System.out.println(counter++));
buttonReset.addActionListener(a -> counter = 0);
If you want to write more than 1 statement, then you can just put your code in curly brackets:
button.addActionListener(a -> {
System.out.println(counter++);
System.out.println("doing more stuff...");
});
JButton has a function called addActionListener. You can pass on an action listener by doing this:
button.addActionListener(() -> {
// Do some logic here
});
Here, I use a lambda expression as an action listener. Within the lambda expression you can place whatever logic you want to have.
Also note that you can add multiple different action listeners to the same button. In a nutshell, the way the JButton interacts with the ActionListeners is based on the observer-pattern.
Imagine this: When the JButton is pressed, it will notify all of it's observers saying "Hey, I have been pressed". Each observer can then independently decide what to do. In case of the JButton, all observers are ActionListeners. If you add multiple ActionListeners then the JButton will notify all of them, and as a result all of their actionPerformed(ActionEvent e) functions are executed. In the example above, I used a lambda expression which then by java is interpreted as an ActionListener.
Other ways to achieve the exact same functionality are:
button.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
// Do some logic here
}
});
In the example above, you use an anonymous class as an actionlistener.
public class MyClass {
public MyClass() {
JButton button = new JButton("press me");
button.addActionListener(new MyActionListener());
}
private class MyActionListener implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
// Do some logic here
}
}
}
In the example above, an inner class is used.
In a nutshell, there is a ton of ways you can make your button have functionality. Above are just a few examples of how to do so.
Does this clarify it a bit more, or do you have some remaining questions?
I have a UI with two components - a JEditorPane and a JComboBox. My goal is to be able to type something into the JEditorPane, select a portion of the text, and while it is still selected type and/or select a value in an editable JComboBox.
This is for a text editor type of program where I want to change the font size of just the selected text in the editor pane. Where the font size is coming from the editable combo box. To clarify, I'm not asking how to apply styles to the text, I'm asking how to select a value in the combo box without losing the focus/selection in the JEditorPane.
Here's the code for the UI, but I wasn't sure where to begin doing anything with the focus...
public static void main(String [] args)
{
JFrame frame = new JFrame();
JPanel contentPane = new JPanel();
JComboBox<String> combo = new JComboBox(new String [] {"Hello", "World"});
contentPane.add(combo);
JEditorPane editor = new JEditorPane();
contentPane.add(editor);
frame.setContentPane(contentPane);
frame.pack();
frame.setVisible(true);
}
I'm asking how to select a value in the combo box without losing the focus/selection in the JEditorPane.
You don't lose the selection of the text in the editor pane when you select an item from the combo box. The selection remains, but it is just not painted until the editor pane regains focus.
So the easiest way to do this is to use a JMenuItem. Read the section from the Swing tutorial on Text Component Features for an example that does this.
If you still want to use the combo box then you can add Integer values to the combo box then the code in your ActionListener for the combo box would look something like:
#Override
public void actionPerformed(ActionEvent e)
{
Integer value = (Integer)comboBox.getSelectedItem();
Action action = new StyledEditorKit.FontSizeAction("Font size", value);
action.actionPerformed(null);
}
The StyledEditorKit actions extend from TextAction. The TextAction knows the last text component that had focus and therefore the font change is applied to that text component.
If you really want the text field to show the selection then you need to create a custom Caret and override the focusLost method to NOT invoke setSelectionVisible(false) (which is the default behaviour.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;
public class DefaultCaretTest extends JFrame
{
public DefaultCaretTest()
{
JTextField textField1 = new JTextField("Text Field1 ");
JTextField textField2 = new JTextField("Text Field2 ");
textField1.setCaret(new SelectionCaret());
textField2.setCaret(new SelectionCaret());
textField1.select(5, 11);
textField2.select(5, 11);
((DefaultCaret)textField2.getCaret()).setSelectionVisible(true);
add(textField1, BorderLayout.WEST);
add(textField2, BorderLayout.EAST);
}
static class SelectionCaret extends DefaultCaret
{
public SelectionCaret()
{
setBlinkRate( UIManager.getInt("TextField.caretBlinkRate") );
}
public void focusGained(FocusEvent e)
{
setVisible(true);
setSelectionVisible(true);
}
public void focusLost(FocusEvent e)
{
setVisible(false);
}
}
public static void main(String[] args)
{
DefaultCaretTest frame = new DefaultCaretTest();
frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
frame.pack();
frame.setLocationRelativeTo( null );
frame.setVisible(true);
}
}
Of course the selection will remain when focus is on any other component, not just the combo box.
You can also use:
comboBox.setFocusable(false);
Since the combo box can't gain focus the focus will remain on the text component, but the problem with this is that the user won't be able to use the keyboard to select a font size from the combo box. A proper GUI design always allows the user to use either the keyboard or the mouse to perform an action.
I want to construct a Swing component JTextField, here is my Code
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class JTextFieldGui{
JTextField textField;
JLabel labelInput;
JLabel labelOutput;
public static void main(String[] args) {
JTextFieldGui gui = new JTextFieldGui();
gui.go();
}
public void go(){
JFrame frame = new JFrame();
JPanel panelInput = new JPanel();
JPanel panelOutput = new JPanel();
labelInput = new JLabel("Your first name: ");
labelOutput = new JLabel("Enter your name, and you will see it here.");
textField = new JTextField(20);
JButton enter = new JButton("Enter");
JButton selectAll = new JButton("Select all text");
frame.setSize(300,200);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
panelInput.setLayout(new BoxLayout(panelInput, BoxLayout.X_AXIS));
textField.addActionListener(new LabelActionListener());
enter.addActionListener(new LabelActionListener());
selectAll.addActionListener(new TextFieldActionlistener());
frame.getContentPane().add(BorderLayout.NORTH, panelInput);
panelInput.add(labelInput);
panelInput.add(textField);
panelInput.add(enter);
panelInput.add(selectAll);
frame.getContentPane().add(BorderLayout.CENTER, panelOutput);
panelOutput.add(labelOutput);
}
class LabelActionListener implements ActionListener{
public void actionPerformed(ActionEvent event){
labelOutput.setText(textField.getText());
}
}
class TextFieldActionlistener implements ActionListener{
public void actionPerformed(ActionEvent event){
textField.selectAll();
}
}
}
Question1: I define the width of the text field in 20 columns, but it always take up a row, like image:
Question2: how to use the selectAll() method, I use it in a listener of the button selectAll, but when I click the button, nothing happens, why
I define the width of the text field in 20 columns, but it always take up a row,
This is the rule of a BoxLayout. A component is resized to fill the space available. A JTextField doesn't have a maximum size so it grows. The buttons and label do have a maximum size so they don't grow.
Don't use a BoxLayout, just use a FlowLayout. It will automatically leave space between each component which is a better layout.
I use it in a listener of the button selectAll, but when I click the button, nothing happens, why
Focus is still on the button. The selected text only displays when the text field has focus.
So in he listener code you need to add:
textField.requestFocusInWindow();
The following code is old:
frame.getContentPane().add(BorderLayout.NORTH, panelInput);
you don't need to get the content pane. You can just add the component to the frame.
the constraint should be the second parameter
there are new constraints to make the names more meaningful
So the code should be:
frame.add(panelInput, BorderLayout.PAGE_START, panelInput);
See the section from the Swing tutorial on How to Use BorderLayout for more information.
Total re-edit with compilable example that clarifies my issue.
Overall program: Class MainFrame displays a JTable with results from a SQL query. MainFrame also has JButtons for refreshing, adding, updating, and querying the table. Clicking the Update button makes visible a text area and submit button. Users can enter an id number into the text area. When they click submit a new frame, UpdateFrame, opens with all the data from the record the corresponds to the id number.
Stripped-down versions of MainFrame and UpdateFrame are below.
UpdateFrame2.java
package kft1task4;
import javax.swing.*;
import java.awt.event.*;
import java.sql.SQLException;
import javax.swing.JScrollPane;
public class UpdateFrame2 extends JFrame implements ActionListener {
JPanel pane = new JPanel();
JTextArea jta = new JTextArea("This is a text area");
UpdateFrame2() {
setVisible(true);
setBounds(1000,400,1000,500);
pane.setLayout(null);
add(pane);
jta.setBounds(110,100,100,15);
pane.add(jta);
}
#Override
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
} //End actionListener
} //End class
Very simple. One frame with one panel with one JTextArea. The JTextArea should be editable; I should be able to type in it.
MainFrame2.java
package kft1task4;
import java.awt.event.*;
import java.sql.SQLException;
import javax.swing.*;
public class MainFrame2 extends JFrame implements ActionListener {
JPanel pane = new JPanel();
JButton closeButt = new JButton("Push me to close the program");
JButton updateButt = new JButton("Push me to update a record");
JButton submitUpdButt = new JButton("Submit");
JLabel updateLabel = new JLabel("Select student id to update");
JTextArea updateTA = new JTextArea();
MainFrame2(){
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(1000,200,1500,1000);
pane.setLayout(null);
add(pane);
updateButt.setBounds(620,550,200,100);
updateButt.addActionListener(this);
pane.add(updateButt);
closeButt.setBounds(1290,550,200,100);
closeButt.addActionListener(this);
pane.add(closeButt);
submitUpdButt.setBounds(820,735,200,25);
submitUpdButt.addActionListener(this);
submitUpdButt.setVisible(false);
pane.add(submitUpdButt);
updateLabel.setBounds(620,700,200,15);
updateLabel.setVisible(false);
pane.add(updateLabel);
updateTA.setBounds(820,700,200,15);
updateTA.setVisible(false);
pane.add(updateTA);
}
#Override
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if(source == closeButt){
System.exit(0);
}
if(source == updateButt){
updateLabel.setVisible(true);
updateTA.setVisible(true);
submitUpdButt.setVisible(true);
}
if(source == submitUpdButt){
//submitUpdButt.setVisible(false);
new UpdateFrame2();
updateTA.setText(null);
updateTA.setVisible(false);
updateLabel.setVisible(false);
submitUpdButt.setVisible(false);
}
}
}
Note the three fields: updateLabel, updateTA, and submitUpdButt (and please forgive the poor naming). When new MainFrame2() is first instantiated, those three fields are .setVisible(False). Clicking updateButt makes them visible.
Click submitUpdButt performs five actions: First, it instantiates a new UpdateFrame2(). Second, it clears the text from UpdateTA. Finally, it makes the three fields invisible. Those 5 actions complete with no problem.
Now here's the oddity: Notice that I've listed "submitUpdButt.setVisible(false)" twice. Once before "new UpdateFrame2()" and once after. I comment out one and leave other in place. If "submitUpdButt.setVisible(false)" appears before "new UpdateFrame2()," the UpdateFrame appears, and its text area is editable.
If "submitUpdButt.setVisible(false)" appears after "new UpdateFrame2()," as it's written above, the UpdateFrame appears. But its text area is not editable.
To clarify: Every other element of the program behaves exactly the same. The 3 fields appear and disappear as expected. The window open and close correctly. The text "This is a text area" appears where it should. No errors are produced. But the text area in UpdateFrame2 is editable or not based on where I put "submitUpdButt.setVisible(false)".
I hope this description is more clear than my last one.
I'm learning Java and GUI. I have some questions, and the first is if there are any major difference between creating a subclass of JFrame and an instance of JFrame. It seems like like a subclass is more powerful? I also wonder if it's necessary to use this code when creating a GUI:
Container contentPane = getContentPane();
contentPane.setLayot(new Flowlayout());
I add my GUI class, it's a simple test so far, to a task that I have to hand in. When a user has entered some text in the textfield and press the button to continue to the next step, how do I do to clear the frame and show a new content or is there a special way to do this is in Java? I guess there must be better to use the same window instead of creating a new!? Help id preciated! Thanks
// Gui class
import java.awt.FlowLayout; // layout
import java.awt.event.ActionListener; // listener
import java.awt.event.ActionEvent; // event
import javax.swing.JFrame; // windows properties
import javax.swing.JLabel; // row of text
import javax.swing.JTextField; // enter text
import javax.swing.JOptionPane; // pop up dialog
import javax.swing.JButton; // buttons
// import.javax.swing.*;
public class Gui extends JFrame {
private JLabel text1;
private JTextField textInput1;
private JTextField textInput2;
private JButton nextButton;
// constructor creates the window and it's components
public Gui() {
super("Bank"); // title
setLayout(new FlowLayout()); // set default layout
text1 = new JLabel("New customer");
add(text1);
textInput1 = new JTextField(10);
add(textInput1);
nextButton = new JButton("Continue");
add(nextButton);
// create object to handle the components (action listener object)
frameHandler handler = new frameHandler();
textInput1.addActionListener(handler);
nextButton.addActionListener(handler);
}
// handle the events (class inside another class inherits contents from class outside)
private class frameHandler implements ActionListener {
public void actionPerformed(ActionEvent event){
String input1 = "";
// check if someone hits enter at first textfield
if(event.getSource() == textInput1){
input1 = String.format(event.getActionCommand());
JOptionPane.showMessageDialog(null, input1);
}
else if(event.getSource() == nextButton){
// ??
}
}
}
}
This small code might help you explain things :
import java.awt.event.*;
import javax.swing.*;
public class FrameDisplayTest implements ActionListener
{
/*
* Creating an object of JFrame instead of extending it
* has no side effects.
*/
private JFrame frame;
private JPanel panel, panel1;
private JTextField tfield;
private JButton nextButton, backButton;
public FrameDisplayTest()
{
frame = new JFrame("Frame Display Test");
// If you running your program from cmd, this line lets it comes
// out of cmd when you click the top-right RED Button.
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
panel = new JPanel();
panel1 = new JPanel();
tfield = new JTextField(10);
nextButton = new JButton("NEXT");
backButton = new JButton("BACK");
nextButton.addActionListener(this);
backButton.addActionListener(this);
panel.add(tfield);
panel.add(nextButton);
panel1.add(backButton);
frame.setContentPane(panel);
frame.setSize(220, 220);
frame.setVisible(true);
}
public void actionPerformed(ActionEvent ae)
{
JButton button = (JButton) ae.getSource();
if (tfield.getText().length() > 0)
{
if (button == nextButton)
{
/*
* this will remove the first panel
* and add the new panel to the frame.
*/
frame.remove(panel);
frame.setContentPane(panel1);
}
else if (button == backButton)
{
frame.remove(panel1);
frame.setContentPane(panel);
}
frame.validate();
frame.repaint(); // prefer to write this always.
}
}
public static void main(String[] args)
{
/*
* This is the most important part ofyour GUI app, never forget
* to schedule a job for your event dispatcher thread :
* by calling the function, method or constructor, responsible
* for creating and displaying your GUI.
*/
SwingUtilities.invokeLater(new Runnable()
{
#Override
public void run()
{
new FrameDisplayTest();
}
});
}
}
if you want to switch (add then remove) JComponents, then you have to
1) add/remove JComponents and then call
revalidate();
repaint()// sometimes required
2) better and easiest choice would be implements CardLayout
If your requirement is to make a wizard, a panel with next and prev buttons, and on clicking next/prev button showing some component. You could try using CardLayout.
The CardLayout manages two or more components (usually JPanel instances) that share the same display space. CardLayout let the user choose between the components.
How to Use CardLayout
If your class extends JFrame, you can do:
getContentPane().removeAll();