java - 在内部框架中绘制多个形状(Jpanels)

Question

我正在用 Java 实现一个演示绘画应用程序。我现在可以绘制单个形状。当我再次尝试绘制时，先前的形状消失了，并且出现了新的形状。我使用 BorderLayut.CENTER 将 JPanel 嵌入到内部框架上。

请帮助我如何在此内部框架中绘制多个形状。

    public class InternalFrame extends JInternalFrame{

    public InternalFrame(String string, boolean b, boolean c, boolean d,
            boolean e) {
        super(string,b,c,d);

        MyShape myShape2 = new MyRectangle();
        add(myShape2, BorderLayout.NORTH);

        MyShape myShape1 = new MyCircle();
        add(myShape1, BorderLayout.SOUTH);      
}   
}

public class MyRectangle extends MyShape {


    public void paintComponent(Graphics g) {
    super.paintComponent(g);
    int temp = 0;

System.out.println("rect");
    // draw circle
    g.setColor(Color.RED);
    g.fillRect(startX, startY, endX - startX, endY - startY);
    g.setColor(Color.GREEN);
    g.drawRect(startX, startY, endX - startX, endY - startY);

}


}


public abstract class MyShape extends JPanel {

    protected int startX;
    protected int startY;
    protected int endX;
    protected int endY;

    MyShape(){
        addMouseListener(new MouseAdapter() {

            public void mousePressed(MouseEvent event) {

//              To initialisise the starting and ending point 
                setStart(0,0);
                setEnd(0,0);
//              To set starting point
                setStart(event.getX(), event.getY());
            }

            // handle mouse release event
            public void mouseReleased(MouseEvent event) {
                setEnd(event.getX(),event.getY());

            }

        });
    }

    public void setStart(int x, int y) {

        startX = x;
        startY = y;

        repaint();
    }

    public void setEnd(int x, int y){

        endX = x;
        endY = y;
        repaint();
    }




}

Answer 1

在 Swing 中绘制是破坏性的，也就是说，每次调用 paintComponent 时，您都需要从头开始重新绘制整个组件状态。

最好的解决方案是生成 Shape 或绘制命令的 List，您每次都可以根据您的要求调用/绘制/填充这些命令paintComponent 被调用

参见Incremental graphics in Swing了解更多细节和想法