How to Use Color Choosers

How to Use Color Choosers

Use the JColorChooser ^[16] class to provide users with a palette of colors to select from. A color chooser is a component that you can place anywhere within your program's GUI. The JColorChooser API also makes it easy to bring up a dialog (modal or not) that contains a color chooser. Figure 5 shows an application that uses a color chooser to set the text color in a banner.

^[16] JColorChooser API documentation: http://java.sun.com/j2se/1.4.2/docs/api/javax/swing/JColorChooser.html.

Figure 5. The ColorChooserDemo application with callouts added to identify the color chooser and the chooser and preview panels.

You can run ColorChooserDemo using Java Web Start or compile the source code yourself. ^[17]

^[17] To run ColorChooserDemo using Java Web Start, click the ColorChooserDemo link on the RunExamples/ components .html page on the CD. You can find the source files here: JavaTutorial/uiswing/components/example-1dot4/index.html#ColorChooserDemo .

The color chooser consists of everything within the box labeled Choose Text Color . This is what a standard color chooser looks like in the Java look and feel. It contains two parts : a tabbed pane and a preview panel. The three tabs in the tabbed pane select chooser panels. The preview panel below the tabbed pane displays the currently selected color.

Here's the code from the example that creates a JColorChooser instance and adds it to the demo's window:

 public class ColorChooserDemo extends JPanel ... {     public ColorChooserDemo() {         . . .         banner = new JLabel("Welcome to the Tutorial Zone!",                             JLabel.CENTER);         banner.setForeground(Color.yellow);         . . .         tcc = new JColorChooser(banner.getForeground());         . . .         add(tcc, BorderLayout.PAGE_END);     }     . . .     frame.setContentPane(new ColorChooserDemo()); 

The JColorChooser constructor in the code snippet takes a Color argument, which specifies the chooser's initially selected color. If you don't specify the initial color, then the color chooser displays Color.white . See the Color ^[18] API for a list of color constants you can use.

^[18] Color API documentation: http://java.sun.com/j2se/1.4.2/docs/api/java/awt/Color.html.

A color chooser uses an instance of ColorSelectionModel to contain and manage the current selection. The color selection model fires a change event whenever the user changes the color in the color chooser. The example program registers a change listener with the color selection model so that it can update the banner at the top of the window. The following code registers and implements the change listener:

 tcc.getSelectionModel().addChangeListener(this); . . . public void stateChanged(ChangeEvent e) {     Color newColor = tcc.getColor();     banner.setForeground(newColor); } 

See How to Write a Change Listener (page 652) in Chapter 10 for general information about change listeners and change events.

A basic color chooser, like the one used in the example program, is sufficient for many programs. However, the color chooser API allows you to customize a color chooser by providing it with a preview panel of your own design, by adding your own chooser panels to it, or by removing existing chooser panels. Additionally, the JColorChooser class provides two methods that make it easy to use a color chooser within a dialog.

Another Example: ColorChooserDemo2

Now let's turn our attention to ColorChooserDemo2 , a modified version of the previous demo program that uses more of the JColorChoos er API. You can run ColorChooserDemo2 using Java Web Start. ^[19] Figure 6 shows a picture of ColorChooserDemo2 .

^[19] To run ColorChooserDemo2 using Java Web Start, click the ColorChooserDemo2 link on the RunExamples/components.html page on the CD. You can find the source files here: JavaTutorial/uiswing/components/example-1dot4/index.html#ColorChooserDemo2 .

Figure 6. The ColorChooserDemo2 application.

This program customizes the banner's text color chooser in these ways:

• Removes the preview panel

• Removes all of the default chooser panels

• Adds a custom chooser panel

Removing or Replacing the Preview Panel (page 171) covers the first customization. Creating a Custom Chooser Panel (page 171) discusses the last two.

The program also adds a button that brings up a color chooser in a dialog, which you can use to set the banner's background color.

Showing a Color Chooser in a Dialog

The JColorChooser class provides two class methods to make it easy to use a color chooser in a dialog. ColorChooserDemo2 uses one of these methods, showDialog , to display the background color chooser when the user clicks the Show Color Chooser... button. Here's the single line of code from the example that brings up the background color chooser in a dialog:

 Color newColor = JColorChooser.showDialog(ColorChooserDemo2.this,                                           "Choose Background Color",                                           banner.getBackground()); 

The first argument is the parent for the dialog, the second is the dialog's title, and the third is the initially selected color.

The dialog disappears under three conditions: (1) the user chooses a color and clicks the OK button, (2) the user cancels the operation with the Cancel button, or (3) the user dismisses the dialog with a frame control. If the user chooses a color, the showDialog method returns the new color. If the user cancels the operation or dismisses the window, the method returns null . Here's the code from the example that updates the banner's background color according to the value returned by showDialog :

 if (newColor != null) {     banner.setBackground(newColor); } 

The dialog created by showDialog is modal. If you want a nonmodal dialog, you can use JColorChooser 's createDialog method to create one. This method also lets you specify action listeners for the OK and Cancel buttons in the dialog window. Use JDialog 's show method to display the dialog created by this method. For an example that uses this method, see Using Other Editors (page 402) in the How to Use Tables (page 388) section later in this chapter.

Removing or Replacing the Preview Panel

By default, the color chooser displays a preview panel. ColorChooserDemo2 removes the text color chooser's preview panel with this line of code:

 tcc.setPreviewPanel(new JPanel()); 

This effectively removes the preview panel because a plain JPanel has no size and no default view. To set the preview panel back to the default, use null as the argument to setPreviewPanel .

To provide a custom preview panel, you also use setPreviewPanel . The component you pass into the method should inherit from JComponent , specify a reasonable size, and provide a customized view of the current color. To be notified when the user changes the color in the color chooser, the preview panel must register as a change listener on the color chooser's color selection model as described previously.

Version Note: In some releases, you either couldn't replace the preview panel or couldn't remove it properly (the titled border would remain ). We believe that both problems have been fixed as of v1.4.2. If your program depends on removing or replacing the preview panel, you should test it against all releases that it supports.

Creating a Custom Chooser Panel

The default color chooser provides three chooser panels:

• Swatches ” for choosing a color from a collection of swatches

• HSB ” for choosing a color using the hue-saturation-brightness color model

• RGB ” for choosing a color using the red-green-blue color model

You can extend the default color chooser by adding chooser panels of your own design with addChooserPanel , or you can limit it by removing chooser panels with removeChooserPanel .

If you want to remove all of the default chooser panels and add one or more of your own, you can do so with a single call to setChooserPanels . ColorChooserDemo2 uses this method to replace the default chooser panels with an instance of CrayonPanel , a custom chooser panel. Here's the call to setChooserPanels from that example:

 //Override the chooser panels with our own. AbstractColorChooserPanel panels[] = { new CrayonPanel() }; tcc.setChooserPanels(panels); 

The code is straightforward: It creates an array containing the CrayonPanel ; next it calls setChooserPanels to set the contents of the array as the color chooser's chooser panels. CrayonPanel is a subclass of AbstractColorChooserPanel and overrides the following five abstract methods defined in its superclass:

void buildChooser()

Creates the GUI that comprises the chooser panel. The example creates one toggle buttons for each of the four crayons and adds them to the chooser panel.

void updateChooser()

This method is called whenever the chooser panel is displayed. The example's implementation of this method selects the toggle button that represents the currently selected color.

 public void updateChooser() {     Color color = getColorFromModel();     if (Color.red.equals(color)) {         redCrayon.setSelected(true);     } else if (Color.yellow.equals(color)) {         yellowCrayon.setSelected(true);     } else if (Color.green.equals(color)) {         greenCrayon.setSelected(true);     } else if (Color.blue.equals(color)) {         blueCrayon.setSelected(true);     } } 

String getDisplayName()

Returns the display name of the chooser panel, which is used on the tab for the chooser panel. Here's the example's getDisplayName method:

 public String getDisplayName() {     return "Crayons"; } 

Icon getSmallDisplayIcon()

Returns a small icon to represent this chooser panel. It's currently unused. Future versions of the color chooser might use this icon or the large one to represent this chooser panel in the display. The example's implementation of this method returns null .

Icon getLargeDisplayIcon()

Returns a large icon to represent this chooser panel. It, too, is currently unused. Future versions of the color chooser might use this icon or the small one to represent this chooser panel in the display. The example's implementation of this method returns null .

The Color Chooser API

Tables 7 through 9 list the commonly used JColorChooser constructors and methods. Other methods you might call are listed in the API tables in The JComponent Class (page 53) in Chapter 3. Refer to the JColorChooser API documentation at: http://java.sun.com/j2se/1.4.2/docs/api/javax/swing/JColorChooser.html.

Table 7. Creating and Displaying the Color Chooser

Method or Constructor	Purpose
JColorChooser() JColorChooser(Color) JColorChooser(ColorSelectionModel)	Create a color chooser. The default constructor creates a color chooser with an initial color of Color.white . Use the second constructor to specify a different initial color. The ColorSelectionModel argument, when present, provides the color chooser with a color selection model.
Color showDialog(Component, String, Color)	Create and show a color chooser in a modal dialog. The Component argument is the dialog's parent, the String argument specifies the dialog's title, and the Color argument specifies the chooser's initial color.
JDialog createDialog(Component, String, boolean, JColorChooser, ActionListener, ActionListener)	Create a dialog for the specified color chooser. As with showDialog , the Component argument is the dialog's parent and the String argument specifies the dialog's title. The other arguments are as follows : the boolean specifies whether the dialog is modal, the JColorChooser is the color chooser to display in the dialog, the first ActionListener is for the OK button, and the second is for the Cancel button.

Table 8. Customizing the Color Chooser's GUI

Method	Purpose
void setPreviewPanel(JComponent) JComponent getPreviewPanel()	Set or get the component used to preview the color selection. To remove the preview panel, use new JPanel() as an argument. To specify the default preview panel, use null.
void setChooserPanel( AbstractColorChooserPanel) AbstractColorChooserPanel[] getChooserPanels()	Set or get the chooser panels in the color chooser.
void addChooserPanel( AbstractColorChooserPanel) AbstractColorChooserPanel removeChooserPanel( AbstractColorChooserPanel)	Add a chooser panel to the color chooser or remove a chooser panel from it.
void setDragEnabled(boolean) boolean getDragEnabled()	Set or get the dragEnabled property, which must be true to enable drag handling on this component. The default value is false. See How to Use Drag and Drop and Data Transfer (page 545) in Chapter 9 for more details. Introduced in 1.4.

Table 9. Setting or Getting the Current Color

Method	Purpose
void setColor(Color) void setColor(int, int, int) void setColor(int) Color getColor()	Set or get the currently selected color. The three-integer version interprets the three integers together as an RGB color. The single-integer version divides the integer into four 8-bit bytes and interprets the integer as an RGB color.
void setSelectionModel( ColorSelectionModel) ColorSelectionModel getSelectionModel()	Set or get the selection model for the color chooser. This object contains the current selection and fires change events to registered listeners whenever the selection changes.

Examples That Use Color Choosers

The following table shows examples that use JColorChooser and where those examples are described.

Example	Where Described	Notes
ColorChooserDemo	This section	Uses a standard color chooser.
ColorChooserDemo2	This section	Uses one customized color chooser and one standard color chooser in a dialog created with showDialog .
TableDialogEditDemo	How to Use Tables (page 388)	Shows how to use a color chooser as a custom cell editor in a table. The color chooser used by this example is created with createDialog .