在Java中是否有可能捕获箭头键，使其以相似的方式工作？Tab移动焦点？

Question

I have a java program that includes a grid of buttons in a jpanel as input interface and a text box to show results. My goal is to be able to control the program with just arrow keys and space.

I know I can progam an event on every button to check if the left key was pressed while that button had the focus and make it pass the focus to the button on the left (and so on).

But I'd like to know if there is another way. I like how Tab and shift+Tab work moving the focus to the previous or next focusable object, and i wonder if it could be done without specific code for every arrow_key-button combination.

Answer 1

You cold write a method for all buttons that handles the arrow up. In this method you store the position of the current button in variables x and y .

Now you loop through all controls on your form and check their positions. Now you need to find one control with the same x but a lower y value (example for arrow up).

If you can´t find such a control, you reached the control of the form that is the "highest".

Note: If your buttons aren´t in a straight rows and columns you need to look for controls that are near the value of you current control instead of exactly the same vlaue.

Hope I could help you.

Answer 2

I have a java program that includes a grid of buttons in a jpanel... My goal is to be able to control the program with just arrow keys and space.

You can use Key Bindings . Key bindings allow you to map an Action to a KeyStroke .

So you can create Key Bindings on the panel to handle the left/right arrow keys.

First you need an Action:

class TabAction extends AbstractAction
{
    private boolean forward;

    public TabAction(boolean forward)
    {
        this.forward = forward;
    }

    public void actionPerformed(ActionEvent e)
    {
        if (forward)
            tabForward();
        else
            tabBackward();
    }

    private void tabForward()
    {
        KeyboardFocusManager manager = KeyboardFocusManager.getCurrentKeyboardFocusManager();
        manager.focusNextComponent();
    }

    private void tabBackward()
    {
        KeyboardFocusManager manager = KeyboardFocusManager.getCurrentKeyboardFocusManager();
        manager.focusPreviousComponent();
    }
}

Now you need to bind the Action to a KeyStroke on your panel:

InputMap im = panel.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT);
KeyStroke tab = KeyStroke.getKeyStroke("TAB");
panel.getActionMap().put(im.get(tab), new TabAction(true));
KeyStroke shiftTab = KeyStroke.getKeyStroke("shift TAB");
im.put(shiftTab, shiftTab);
panel.textArea.getActionMap().put(im.get(shiftTab), new TabAction(false));

You would typically invoke the above code in the constructor of your panel containing the buttons, so "panel" would really be "this".

Read the section from the Swing tutorial on How to Use KeyBindings for more information.