JComponent尺寸问题

Question

我有一个JComponent子类，用于在屏幕上绘制形状。在构造函数中，我试图将ballX和ballY设置为JComponent的X和Y大小值的一半，我认为我做错了。我已经查了很多次了，找不到补救办法。代码如下。请记住，这是我第一次真正的Swing/Graphics2D冒险。

public class PongCanvas extends JComponent {
//Vars to hold XY values and Dimension values.

    private int batXDim, batYDim;
    private int b1X, b1Y;
    private int b2X, b2Y;
    private int ballRad, ballX, ballY;

    public PongCanvas() {//Instantiate vars.
        batXDim = 20;
        batYDim = 100;

        b1X = 0;
        b1Y = 0;

        b2X = 0;
        b2Y = 0;

        ballRad = 20;
        ballX = getWidth() / 2;
        ballY = getHeight() / 2;
    }

    public void paint(Graphics g) {//Main paint Method.
        //Cast Graphics to Graphics2D.
        Graphics2D g2 = (Graphics2D) g;
        //Enable antialiasing.
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);
        //Draw background.
        g2.setPaint(Color.black);
        g2.fillRect(0, 0, getWidth(), getHeight());
        //Draw ball.
        g2.setPaint(Color.white);
        g2.fillOval(ballX, ballY, ballRad, ballRad);
        //Draw bat 1.
        g2.fillRect(b1X, b1Y, batXDim, batYDim);
        //Draw bat 2.
        g2.fillRect(b2X, b2Y, batXDim, batYDim);
    }
}

Answer 1

在getPreferredSize()中重写JComponent以返回首选的大小，并以该Dimension的一半宽度和高度开始。为了同一目的，这个KineticModel调用DisplayPanel中的setPreferredSize()。

增编:作为解释，您当前的方法失败了，因为来自getWidth()和getHeight()的结果是无效的，直到在容器上调用了validate()，通常是pack()的结果。

Answer 2

我同意垃圾神的回答。(+1)

将ballX和ballY在paintComponent(g)中移动如下

if (ballX==0 && ballY==0) {
    ballX = getWidth()/2;
    ballY = getHeight()/2;
}