图形未绘制/显示 [英] Graphics Not Drawn/Appearing

问题描述

我遇到了这样的问题，即我绘制的对象没有出现在GUI中.我知道它正在处理中，因为数据被推送到日志文件中.但是，该图形没有出现.

I'm having this problem where an object that I've drawn isn't appearing in the GUI. I know it's being processed because data is being pushed to a log file. However, the graphic isn't appearing.

这是我的一些代码:

public static void main(String[] args)
{
   JFrame window = new JFrame();
   window.setLayout(new BorderLayout());
   window.setVisible(true);
}

我在这里和那里放置了一个按钮和其他一些小部件.中央窗格(BorderLayout.CENTER)是显示我的DrawnObject的地方.

There's a button and a few other widgets that I've placed here and there. The center pane (BorderLayout.CENTER) is where my DrawnObject is to be displayed.

// Called when button is pushed/clicked
public static void trigger()
{
   DrawnObject shape = new DrawnObject();
   window.setLayout(new BorderLayout());
   window.getContentPane().add(shape, BorderLayout.CENTER);
   window.pack;
}

public class DrawnObject extends JComponent()
{
   @Override
   public Dimension getMinimumSize()
   {
       return new Dimension(100, 100);
   }

   @Override
   public Dimension getPreferredSize()
   {
       return new Dimension(500, 500);
   }

   @Override
   public Dimension getMaximumSize()
   {
       return new Dimension(700, 700);
   }

   @Override
   public void paintComponent(Graphics g)
   {
      super.paintComponent(g);
      g.setColor(Color.RED);
      g.fillRect(10, 10, 10, 10);
   }
}

我尝试将Graphics对象转换为Graphics2D并使用适当的绘制方法，但这没有帮助.

I've tried casting the Graphics object as Graphics2D and using the appropriate draw methods, but that hasn't helped.

推荐答案

尝试更改颜色...

super.paintComponent(g);
g.setColor(Color.RED);
g.fillRect(10, 10, 10, 10);

默认情况下，图形上下文颜色设置为组件背景颜色

The graphics context color is set to the components background color by default

public class PaintTest01 {

    public static void main(String[] args) {
        new PaintTest01();
    }

    public PaintTest01() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new DrawPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class DrawPane extends JPanel {

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(30, 30);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setColor(Color.RED);
            g.fillRect(10, 10, 10, 10);
        }
    }
}

已更新

根据问题中的更新代码，无法编译...

From your updated code in your question, it can't compile...

您在构造函数中创建一个名为JFrame的窗口，这是一个局部变量...

You create a JFrame named window in the constructor, which is a local variable...

public static void main(String[] args)
{
   JFrame window = new JFrame();
   window.setLayout(new BorderLayout());
   window.setVisible(true);
}

然后尝试将DrawObject添加到窗口中...

Then you try and add the DrawObject to the window...

public static void trigger()
{
   DrawnObject shape = new DrawnObject();
   window.setLayout(new BorderLayout());
   window.getContentPane().add(shape, BorderLayout.CENTER);
   window.pack;
}

但是由于window是未定义的，因此您的示例无法编译.

But because window is undefined, you example can't compile.

唯一可以编译的方法是，如果您在类级别上有一个名为window的静态变量，在这种情况下，除非您已初始化该变量，否则它应该生成一个NullPointerException

The only way that this would compile is if you had a static variable at the class level called window, which in that case, it should be producing a NullPointerException, unless you've initialised that variable

public class MyDrawing {
    public static JFrame window = new JFrame();

这意味着您有两个框架，一个是在构造函数中创建的，另一个是作为静态级别类字段创建的.这是行不通的，因为它们是不同的实例

This would mean you have two frames, one you created in the constructor and one your create as a static level class field. This won't work, because they are different instances

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