Question

可能重复：
paintComponent () never executes on a JFrame

我使用以下代码显示两个字符串，我直接在jfame上绘制它们而不是将它们添加为组件或jpanel.But为什么我得到一个空白窗口而不是获取字符串。我错了？

import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JFrame;
import javax.swing.SwingUtilities;


public class SimpleAttributes extends JFrame{

SimpleAttributes()
{

    super("Simple Attributes");
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(300, 200);
    //setUndecorated(true);
    Container cp=this.getContentPane();
    cp.setBackground(new Color(0,200,0,0));

    setVisible(true);
}

public void paintComponent(Graphics g)
{
    Graphics2D g2=(Graphics2D)g.create();
    g2.setColor(Color.RED);
    g2.drawString("One", 10, 10);

    g.drawString("Two", 10,40);

}
public static void main(String[] args) {
    // TODO Auto-generated method stub
SwingUtilities.invokeLater(new Runnable(){public void run(){new SimpleAttributes();}});
}

}

Answer 1

JFrame不是一个组件，因此没有paintComponent()函数。 See the API documentation

Answer 2

如上所述，上述情况不正确，没有这样的方法，（我打算快速打字）并考虑JPanels。

您可以创建自己的Container并覆盖paint()方法，然后将ContentPane用作frame.setContentPane(Container con)：

import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class SimpleAttributes extends JFrame {

    SimpleAttributes() {

        super("Simple Attributes");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(300, 200);
        //setUndecorated(true);
        setContentPane(new MyContainer());
        getContentPane().setBackground(new Color(0, 200, 0, 0));

        setVisible(true);
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        SwingUtilities.invokeLater(new Runnable() {

            public void run() {
                new SimpleAttributes();
            }
        });
    }
}

class MyContainer extends Container {

    @Override
    public void paint(Graphics g) {
        super.paint(g);
        Graphics2D g2 = (Graphics2D) g.create();
        g2.setColor(Color.RED);
        g2.drawString("One", 10, 10);
        g.drawString("Two", 10, 40);
    }
}

如对一个答案的评论中所述，您可以使用paint()的{{1}}来补偿对话框标题的偏移量：

JFrame

但是所有这些只会让你更加头疼，为什么不把它作为首选方式呢？ import java.awt.Color; import java.awt.Container; import java.awt.Graphics; import java.awt.Graphics2D; import javax.swing.JFrame; import javax.swing.SwingUtilities; public class SimpleAttributes extends JFrame { SimpleAttributes() { super("Simple Attributes"); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); setSize(300, 200); //setUndecorated(true); getContentPane().setBackground(new Color(0, 200, 0, 0)); setVisible(true); } @Override public void paint(Graphics g) { super.paint(g); Graphics2D g2 = (Graphics2D) g.create(); g2.setColor(Color.RED); g2.drawString("One", 10, 10);//wont show g2.drawString("One", 50, 50);//will show g.drawString("Two", 40, 40);//will show } public static void main(String[] args) { // TODO Auto-generated method stub SwingUtilities.invokeLater(new Runnable() { public void run() { new SimpleAttributes(); } }); } }并覆盖JPanel

在摇摆gui得到空白的窗口

2 个答案: