java - JComponent 大小问题

Question

我有一个 JComponent 子类，我用它在屏幕上绘制形状。在构造函数中，我尝试将 ballX 和 ballY 设置为 X 和 Y 大小值的一半JComponent，我想我做错了。我现在已经查了很多，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

覆盖 getPreferredSize()在您的 JComponent 中返回您的首选大小，并从该 Dimension 的宽度和高度的一半开始。为了同样的目的，这 KineticModel在 DisplayPanel 中调用 setPreferredSize() .

附录:作为解释，您当前的方法失败是因为 getWidth() 和 getHeight() 的结果无效，直到 validate() 已在封闭容器上调用，通常是 pack() 的结果.