java - 重写 JComponent 方法

Question

运行此代码后，出现的窗口大小为 0x0。我可以通过编写“f.setSize(640, 480);”来修复它在主要方法中。我听说它的做法很糟糕，所以..有没有办法让这个压倒性的工作发挥作用？

public class Gui {

    public static void main(String[] args) throws IOException {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().setBackground(Color.BLACK);
        f.add(new DrawingPad());
        f.setVisible(true); 
    }
 }

class DrawingPad extends JComponent{
    Image img = new ImageIcon("res/icon.jpg").getImage();
    Dimension d = new Dimension(640, 480);

    public void paintComponent(Graphics g){
        g.drawImage(img, 50, 50, null);
    }

    @Override
    public Dimension getPreferredSize(){return d;}
}

Answer 1

在使框架可见之前调用f.pack()。

引自 javadoc :

Causes this Window to be sized to fit the preferred size and layouts of its subcomponents. The resulting width and height of the window are automatically enlarged if either of dimensions is less than the minimum size as specified by the previous call to the setMinimumSize method.

此外，您不应该在主线程中使用 swing 组件。仅来自事件调度线程。阅读 http://docs.oracle.com/javase/tutorial/uiswing/concurrency/initial.html