0

使用 Java Graphics，我尝试绘制一个简单的矩形。

因为Applet它运行良好，但是当我用它在 a 上显示时JFrame，矩形即将出现，但有一些不寻常的背景

这是编码：

package graphicsex;

import java.awt.Graphics;

public class Graphics2 extends javax.swing.JFrame {

    public static void main(String[] args) {
        Graphics2 inst = new Graphics2();
        inst.setVisible(true);
    }

    public Graphics2() {
        super();
        initGUI();
    }

    private void initGUI() {
        try {
            setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
            pack();
            setSize(400, 300);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void paint(Graphics g) {
        g.drawRect(10, 20, 30, 40);
    }
}

然后我尝试JTextArea使用这两个类，但在这种情况下，矩形根本没有显示。

GraphicsEx1.java:

package graphicsex;

import javax.swing.JTextArea;
import java.awt.Graphics;

public class GraphicsEx1 extends javax.swing.JFrame {

    private JTextArea jTextArea1;

    {
        //Set Look & Feel
        try {
            javax.swing.UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        GraphicsEx1 inst = new GraphicsEx1();
        inst.setVisible(true);
    }

    public GraphicsEx1() {
        super();
        initGUI();
    }

    private void initGUI() {
        try {
            setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
            getContentPane().setLayout(null);
            {
                jTextArea1 = new JTextArea();
                getContentPane().add(jTextArea1);
                jTextArea1.setBounds(7, 7, 371, 245);
                jTextArea1.setEnabled(false);
            }
            pack();
            setSize(400, 300);
        } catch (Exception e) {
            e.printStackTrace();
        }
        postInitGUI();
    }

    public void postInitGUI() {
        DisplayItems dp = new DisplayItems();
        jTextArea1 = dp;
        dp.setVisible(true);
        this.add(jTextArea1);
    }
}

和 DisplayItems.java：

package graphicsex;

import java.awt.Dimension;
import java.awt.Graphics;

public class DisplayItems extends javax.swing.JTextArea {

    public DisplayItems() {
        super();
        initGUI();
    }

    private void initGUI() {
        try {
            setPreferredSize(new Dimension(400, 300));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void paint(Graphics g) {
        g.drawRect(10, 20, 50, 100);
        g.drawString("Kalai", 90, 150);
    }
}

任何人都可以帮我在JFrame,JPanel orJTextarea 等任何摆动容器上显示图形组件吗？

4

2 回答 2

4

It is inadvisable to override the paint method of a top level container...

JFrame contains a number of important layers onto which many other components are placed, buy doing this...

public void paint(Graphics g){
    g.drawRect(10,20,30,40);
}

You've successfully stopped any of the child components from begin painted, or in fact, anything other then your rectangle.

enter image description here

(The secret life of a top level swing container - Picture taken from How to use Root Panes)

While some might suggest simple adding a call to super.paint(g), I would not recommend it.

Better to use something like the JFrame's glass pane...This will allow you to paint over the components that reside within the frame. If you need to paint under the components, replace the JFrame's content pane instead.

You may find...

Of use...

Update

I think I'm beginning to see you problem with trying to perform custom painting on a text area.

The problem is, paintComponent paints the background AND the text in one foul swoop, meaning that any painting you do before calling super.paintComponent will be rendered over, but any painting done over it will paint over the text.

You could set the text area to be non-opaque and paint the background yourself...

enter image description here

public class CustomTextArea extends JTextArea {

    public CustomTextArea() {
        setOpaque(false);
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(200, 200);
    }

    @Override
    protected void paintComponent(Graphics g) {
        g.setColor(getBackground());
        g.fillRect(0, 0, getWidth(), getHeight());
        g.setColor(Color.RED);
        g.fillRect(0, 0, 100, 100);
        super.paintComponent(g);
    }

}

The problem is though, it's easy for people to rest the opaque level and destroy your work. Sure you could override the setOpaque or getOpaque, but how do you known when the user actually wants to set the component transparent, so you can stop fill the back ground?

于 2013-01-04T06:56:54.467 回答
0

* 使用 jPanel *

使用jpanel，可以绘制图形元素；

import java.awt.Graphics;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.WindowConstants;

public class GraphicsEx1 extends javax.swing.JFrame {
private JScrollPane jsp1;
private JTextArea jta1;
private JPanel jpnl1;

{
//Set Look & Feel
try {
javax.swing.UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsClassicLookAndFeel");
} catch(Exception e) {e.printStackTrace();}
}

public static void main(String[] args) {
GraphicsEx1 inst = new GraphicsEx1();
inst.setLocationRelativeTo(null);
inst.setVisible(true);
}

public GraphicsEx1() {
super();
initGUI();
postInitGUI();
}

private void initGUI() {
try {
setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
getContentPane().setLayout(null);
{
jsp1 = new JScrollPane();
getContentPane().add(jsp1);
jsp1.setBounds(10, 32, 372, 223);
{
jpnl1 = new JPanel();    //<----------------
jsp1.setViewportView(jpnl1);    //<----------------
jpnl1.setBackground(new java.awt.Color(255,255,255));
jpnl1.setLayout(null);
//jpnl1.setPreferredSize(new java.awt.Dimension(359, 327));
}
}
pack();
setSize(400, 300);
} catch (Exception e) {e.printStackTrace();}
}

public void postInitGUI(){
frmGrpView gp=new frmGrpView();
jta1=new JTextArea();
jta1=gp;
jta1.setBounds(0,0, 336, 197);
jta1.setVisible(true);
//jpnl1.setBounds(0, 0, 336, 197);
jpnl1.add(jta1);    //<----------------
jpnl1.revalidate();
jsp1.revalidate();
}
}
//----------------------- Second Class --------------------------
class frmGrpView extends JTextArea{
public frmGrpView() {
super();
setEditable(false);
}
public void paint(Graphics g){
super.paint(g);
g.drawRect(10, 10, 100, 100);
}
}
于 2013-01-06T18:57:15.600 回答