用新的替换旧的JButton

Question

I've created an array of buttons:

JButton bt[][]=new JButton[8][8];

And then I call a function called refreshBoard in the following way

public void refreshBoard() {
    for (int i = 0; i < 8; i++) {
        for (int j = 0; j < 8; j++) {
            bt[i][j] = new JButton(); 
            bt[i][j].setIcon(new javax.swing.ImageIcon("icons/"+ board[i][j] +".png"));
                panel.add(bt[i][j);   
        }
    }  

The value in board[i][j] controls which image is to be displayed on the button. I call this refreshBoard function at intervals. The problem is that when i call the function the second time it adds 64(8X8) new buttons rather than replacing the already displayed ones. How do i make it replace the old buttons instead of adding new ones.

Answer 1

This line bt[i][j] = new JButton() creates new buttons all the time you hit refreshBoard() board. This is not right.

Do as this:

Make panel instance variable so that it can be accessed by all instance methods .

Add board:

public void addBoard() {
    for (int i = 0; i < 8; i++) {
        for (int j = 0; j < 8; j++) {
            bt[i][j] = new JButton(); 
            bt[i][j].setIcon(new javax.swing.ImageIcon("icons/"+ board[i][j] +".png"));
                panel.add(bt[i][j);   
        }
    }  

Refresh Board:

To refresh board, you will have to extract the buttons from JPanel and then use them:

JButton button = null;
Component[] components = panel.getComponents();

public void refreshBoard() {
    for (int i = 0; i < components.length; i++) {

        if (components[i] instanceof JButton) {
            button = (JButton) components[i];
            button.setIcon(<set the icon however you want. extracting from the `board[][]` or by creating new ones>));
        }

    }
} 

You can also put the check to know what JButton you are extracting:

String buttonText = button.getText();

Note: You don't need to replace your old buttons when you hit Refresh, just extract from the panel and set the icon on them as I have done in above code.

Answer 2

You would need to remove your layout on the panel and recreate your layout with the new buttons you want to use I believe. There may be a way to remove an item from a layout but i've found it easier to re-redo the layout when i want to do something like this. It may be simpler to keep the same 64 buttons but store them maybe in an array or an array list and update the icons that you set on these buttons in refreshboard. From a design standpoint it makes sense if the 64 buttons are a fixed element and the icon is changing, you would only change the icons.

Answer 3

The line:

        panel.add(bt[i][j); 

simply adds the new buttons to the panel. If you call it twice, you got twice worth of buttons added. You have to remove the old ones before you add the new ones.

However, is there any reason why you have to create all 64 JButton every time you refresh? It creates a lot of Java objects which is not desired. Could you simply set the icon to existing buttons without recreating new ones every time you refresh?

Answer 4

我不确定，但是也许您应该调用panel.repaint（）？

Answer 5

Either explicitly remove them by looping over them (with null checks). Or, in your nested for-loop, replace the first line with the following.

if(!(bt[i][j] instancceof JButton)) {
    bt[i][i] = new JButton();
}