如何使用 CardLayout

If you are interested in using JavaFX to create your GUI, see Working With Layouts in JavaFX.

The following figure represents a snapshot of an application that uses the CardLayout class to switch between two panels.

Click the Launch button to run CardLayoutDemo using Java™ Web Start (download Java SE). Alternatively, to compile and run the example yourself, consult the example index.

The complete code of this demo is in the CardLayoutDemo.java file.

The CardLayout class manages two or more components (usually JPanel instances) that share the same display space. When using the CardLayout class, let the user choose between the components by using a combo box. The CardLayoutDemo application is an example to illustrate this feature.

Another way to accomplish the same task is to use a tabbed pane. The following picture shows a tabbed pane version of the preceding example:

Because a tabbed pane provides its own GUI, using a tabbed pane is simpler than using the CardLayout class. For example, implementing the preceding example using a tabbed pane results in a program with fewer lines of code.

Click the Launch button to run TabDemo using Java™ Web Start (download JDK 7 or later). Alternatively, to compile and run the example yourself, consult the example index.

The complete code of this demo is in the TabDemo.java file.

Conceptually, each component that a CardLayout manages is like a playing card or trading card in a stack, where only the top card is visible at any time. You can choose the card that is showing in any of the following ways:

• By asking for either the first or last card, in the order it was added to the container
• By flipping through the deck backwards or forwards
• By specifying a card with a specific name

The CardLayoutDemo class uses the last scheme.

The following code snippet from the CardLayoutDemo.java application creates the CardLayout object and the components it manages.

//Where instance variables are declared:
JPanel cards;
final static String BUTTONPANEL = "Card with JButtons";
final static String TEXTPANEL = "Card with JTextField";

//Where the components controlled by the CardLayout are initialized:
//Create the "cards".
JPanel card1 = new JPanel();
...
JPanel card2 = new JPanel();
...

//Create the panel that contains the "cards".
cards = new JPanel(new CardLayout());
cards.add(card1, BUTTONPANEL);
cards.add(card2, TEXTPANEL);

To add a component to a container that a CardLayout object manages, specify a string that identifies the component being added. For example, in this demo, the first panel has the string "Card with JButtons", and the second panel has the string "Card with JTextField". In this demo those strings are also used in the combo box.

To choose which component a CardLayout object shows, put additional code in your code example:

//Where the GUI is assembled:
//Put the JComboBox in a JPanel to get a nicer look.
JPanel comboBoxPane = new JPanel(); //use FlowLayout
String comboBoxItems[] = { BUTTONPANEL, TEXTPANEL };
JComboBox cb = new JComboBox(comboBoxItems);
cb.setEditable(false);
cb.addItemListener(this);
comboBoxPane.add(cb);
...
pane.add(comboBoxPane, BorderLayout.PAGE_START);
pane.add(cards, BorderLayout.CENTER);
...

//Method came from the ItemListener class implementation,
//contains functionality to process the combo box item selecting
public void itemStateChanged(ItemEvent evt) {
    CardLayout cl = (CardLayout)(cards.getLayout());
    cl.show(cards, (String)evt.getItem());
}

This example shows that to use the show method of the CardLayout class, you must set the currently visible component. The first argument in the show method is the container the CardLayout controls — that is, the container of the components the CardLayout manages. The second argument is the string that identifies the component to show. This string is the same string that was used when adding the component to the container.

The CardLayout API

The following table lists the CardLayout class methods that are used to choose a component. For each method, the first argument is the container for which the CardLayout is the layout manager (the container of the cards the CardLayout controls).

Examples that Use CardLayout

Only one example in this trail uses CardLayout, and this is the CardLayoutDemo. Generally, our examples use tabbed panes instead of CardLayout, since a tabbed pane provides its own GUI.