java - 基本绘画代码。这不起作用

Question

我试图在 JFrame 内的 MainPanel 内的 JPanel 内绘制一个矩形。在主类中，我初始化一个 RoomView:

roomView = new RoomView(newropc,"Default");

然后我执行:

private void init_panels() {
    mainPanel.setLayout(new BorderLayout());
    mainPanel.add(toolsPanel,BorderLayout.SOUTH);
    mainPanel.add(roomView,BorderLayout.EAST);
    mainPanel.add(libraryPanel,BorderLayout.WEST);
}

然后类roomview执行:

public class RoomView extends JPanel{
    private RoomPController rpc;
    private double w, h;
    int qFactor;
    Vector v;
    String roomName;
    DrawingPanelVector dpv;


public RoomView(RoomPController newRpc, String newRoomName) {
setPreferredSize(new Dimension(600,350));
    rpc = newRpc;
w = 0;
h = 0;
qFactor = 1;
v = new Vector();
roomName = newRoomName;
    v.add(new GraphicRectangle(0, 0, (int)(w*qFactor), (int)(h*qFactor), Color.black));
    dpv = new DrawingPanelVector(v);
    add(dpv);
    setVisible(true);
    getPreferredSize();
}

public void RepaintRoom() {
    Scanner c = new Scanner(System.in);
    v = new Vector();
    w = rpc.getRoomW(roomName);
    h = rpc.getRoomL(roomName);
    System.out.println("Room w = " + w + " Room h = " + h);
    System.out.println("Height = " + getHeight() + " Width = " + getWidth());
    if ((double)getHeight()/h < (double)getWidth()/w) qFactor = (int)((double)getHeight()/h);
    else qFactor = (int)((double)getWidth()/w);
    System.out.println("qFactor = " + qFactor);
    v.add(new GraphicRectangle(0, 0, (int)(w*qFactor), (int)(h*qFactor), Color.black));
    dpv = new DrawingPanelVector(v);
    add(dpv);
    setVisible(true);
}
}

最后，DrawingPanelVector 是:

public class DrawingPanelVector extends JPanel {
    // variable miembro
    private Vector v;
    // constructor
    public DrawingPanelVector(Vector va) {
        super(new FlowLayout());
        setPreferredSize(new Dimension(600,350));
        v = va;
        getPreferredSize();
    }
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Drawable dib;
        Iterator it;
        it = v.iterator();
        while (it.hasNext()) {
        dib = (Drawable) it.next();
        dib.draw(g);
    }
}
}

它不执行任何操作，主面板上也不会显示任何内容。
这让我抓狂，我必须在 7 小时内将这段可以运行的代码交给我的老师。

Answer 1

据我所知，最初的问题是......

你打电话...

roomView = new RoomView(newropc,"Default");

这调用...

public RoomView(RoomPController newRpc, String newRoomName) {
    setPreferredSize(new Dimension(600,350));
    rpc = newRpc;
    w = 0;
    h = 0;
    qFactor = 1;
    v = new Vector();
    roomName = newRoomName;
    getPreferredSize();
}

这不会给组件添加任何内容。没有将 DrawingPaneVector 添加到您的 RoomView 中，这意味着不会绘制任何内容...

附加

你违反了油漆链。绘制过程是一个复杂的系统，涉及到许多子方法和委托(delegate)。通过重写 paint 方法并未能调用 super.paint，您就绕过了整个绘画过程。

相反，您应该重写 paintComponent 并确保调用 super.paintComponent 以确保 paintComponent 需要执行的工作得到完成...

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Drawable dib;
    Iterator it;
    it = v.iterator();
    while (it.hasNext()) {
        dib = (Drawable) it.next();
        dib.draw(g);
    }
}

看看Performing Custom Painting和 Painting in AWT and Swing了解更多详情。

不鼓励使用setPreferredSize，主要问题是这很容易被程序的其他部分更改。相反，您应该重写自定义组件的 getPreferredSize。

更多附加内容

我建议放弃使用Vector，而是使用List，实例化ArrayList的实现。 Vector 的唯一好处是它是同步的，但我看不出您想要这样做的任何理由。

我还建议阅读 Generics 。这将使您在长期错误中的生活变得更轻松，因为您不需要转换对象。

使用 List 和泛型实现 DrawingPanelVector 面板的可能实现...

public class DrawingPanelVector extends JPanel {

    private List<Drawable> drawables;

    public DrawingPanelVector() {
        drawables = new ArrayList<>(25);
    }

    public void add(Drawable drawable) {
        drawables.add(drawable);
        repaint();
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(600, 350);
    }

    // redefinición del método paint()
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        for (Drawable drawable : drawables) {
            drawable.draw(g);
        }
    }
}