尽管使用了setText函数，但在JTextArea中没有显示

时间：2014-07-02 06:56:22

标签： java swing jtextarea mouselistener

在这里，我希望通过创建前一个类的对象来显示一个类的MouseEvents ... ... 

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.lang.*;
public class MyPagalpanti extends JPanel implements MouseListener
{Point a,b;
boolean drawLin,drawOvl,drawOvl2;
MyPagalpanti(){a=new Point(0,0);b=new Point(0,0);drawLin=false;drawOvl=false,drawOvl2=false;;setSize(300,300);addMouseListener(this);}
public void mouseClicked(MouseEvent m)
{if(!drawOvl){a=new Point(m.getX(),m.getY());drawOvl=true;drawOvl2=false;}
else {b=new Point(m.getX(),m.getY());drawOvl=true;drawOvl2=true;repaint();}//record("clicked",m);}
}
public void mouseEntered(MouseEvent m)
{
}
public void mousePressed(MouseEvent m)
{a=new Point(m.getX(),m.getY());repaint();}
public void mouseReleased(MouseEvent m)
{b=new Point(m.getX(),m.getY());}
public void mouseExited(MouseEvent m)
{}
public void paintComponent(Graphics g)
{if(drawLin){g.setColor(Color.yellow);g.drawLine((int)a.getX(),(int)a.getY(),(int)b.getX(),(int)b.getY());}//d=0;}
else if(drawOvl&&drawOvl2){g.setColor(Color.red);int width=(int)Math.abs(b.getX()-a.getX());
int h=(int)Math.abs(b.getY()-a.getY());
g.drawOval((int)a.getX(),(int)a.getY(),width,h);
}}
}

形成MyPagalpanti对象的类：

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
//import java.swing.JPanel.*;

public class Mithu extends JFrame// implements MouseListener
{JTextArea jta1,jta2;
Mithu(String title)
{
super(title);
MyPagalpanti p1=new MyPagalpanti();
jta1=new JTextArea();
jta2=new JTextArea();
p1.setOpaque(true);
jta1.setEditable(false);
jta2.setEditable(false);
setForeground(Color.blue);
p1.setPreferredSize(new Dimension(600,600));
p1.setLayout(new GridLayout(3,1,0,0));
getContentPane().add(p1);
pack();
setVisible(true);
}
void record(String s,MouseEvent e)
{jta1.setText(jta1.getText()+"\n"+s+""+e.toString());}
public void mouseClicked(MouseEvent m)
{record("clicked",m);}
public void mouseEntered(MouseEvent m)
{record("entered",m);}
public void mousePressed(MouseEvent m)
{record("pressed",m);}
public void mouseReleased(MouseEvent m)
{ record("released",m);}
public void mouseExited(MouseEvent m)
{record("exited",m);}

public static void main(String args[])
{Mithu m=new Mithu("HI ! Karamvir");
m.setVisible(true);}
}

请不要一字一句地去...我知道我的代码还有很多其他的错误...因为我还在努力......但是对于那些说“MouseEvents只会传递到它注册的组件中的MouseListener“，我猜你说得对，但如果仔细观察，我只使用了这个概念......在这段代码中......

3 个答案:

答案 0 :(得分：4)

添加它JBNizet的答案......

MouseListeners只会传递给可显示且已注册通知的组件。创建一个正在侦听鼠标事件并将其添加到组件中的组件不会神奇地将这些事件传递给您的组件。

然后，在此之前，您要将两个组件添加到由CENTER管理的组件的默认（BorderLayout）位置... 

getContentPane().add(panelTop);
//...
getContentPane().add(p1);

这有效地使第一个组件不可见，这意味着它不可显示......

  • 您不应该因为它已被弃用而致电show，而是使用setVisible。
  • 在进行任何自定义绘画之前，您应该在super.paintComponent方法中调用paintComponent，否则最终会无法完成绘画问题
  • paintComponent不需要public，因为您从不希望任何人直接调用它...

<强>更新

除非您注册了有关事件通知的兴趣，否则您将永远不会收到通知，无论您创建的对象或您实施的界面如何。

就像说“我对这部电影感兴趣”，但除非你去电影院，否则你永远不会看到它......

为了让您的Mithu类接收鼠标事件通知，它必须针对它有兴趣监视的组件注册MouseListener。

以下示例在MouseListener类中针对Mithu实例注册aa MyPagalpanti，这允许它接收由MyPagalpanti实例生成的鼠标事件

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestMouseListener {

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

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

                Mithu m = new Mithu("HI ! Karamvir");
                m.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                m.pack();
                m.setLocationRelativeTo(null);
                m.setVisible(true);
            }
        });
    }

    public class Mithu extends JFrame implements MouseListener
    {

        JTextArea jta1;

        Mithu(String title) {
            super(title);
            MyPagalpanti p1 = new MyPagalpanti();
            p1.addMouseListener(this);
            jta1 = new JTextArea();
            p1.setOpaque(true);
            jta1.setEditable(false);
            setForeground(Color.blue);
            setLayout(new GridLayout(2, 1));
            getContentPane().add(jta1);
            getContentPane().add(p1);
            pack();
            setVisible(true);
        }

        void record(String s, MouseEvent e) {
            jta1.append("\n" + s + "" + e.toString());
        }

        public void mouseClicked(MouseEvent m) {
            record("clicked", m);
        }

        public void mouseEntered(MouseEvent m) {
            record("entered", m);
        }

        public void mousePressed(MouseEvent m) {
            record("pressed", m);
        }

        public void mouseReleased(MouseEvent m) {
            record("released", m);
        }

        public void mouseExited(MouseEvent m) {
            record("exited", m);
        }
    }

    public class MyPagalpanti extends JPanel implements MouseListener {

        Point a, b;
        boolean drawLin, drawOvl, drawOvl2;

        MyPagalpanti() {
            a = new Point(0, 0);
            b = new Point(0, 0);
            drawLin = false;
            drawOvl = false;
            drawOvl2 = false;
            setSize(300, 300);
            addMouseListener(this);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

        public void mouseClicked(MouseEvent m) {
            if (!drawOvl) {
                a = new Point(m.getX(), m.getY());
                drawOvl = true;
                drawOvl2 = false;
            } else {
                b = new Point(m.getX(), m.getY());
                drawOvl = true;
                drawOvl2 = true;
                repaint();
            }//record("clicked",m);}
        }

        public void mouseEntered(MouseEvent m) {
        }

        public void mousePressed(MouseEvent m) {
            a = new Point(m.getX(), m.getY());
            repaint();
        }

        public void mouseReleased(MouseEvent m) {
            b = new Point(m.getX(), m.getY());
        }

        public void mouseExited(MouseEvent m) {
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setColor(Color.RED);
            FontMetrics fm = g.getFontMetrics();
            if (a != null && b != null) {
                g.drawString(a + "-" + b, 0, fm.getHeight());
            }
            if (drawLin) {
                g.setColor(Color.yellow);
                g.drawLine((int) a.getX(), (int) a.getY(), (int) b.getX(), (int) b.getY());
            }//d=0;}
            else if (drawOvl && drawOvl2) {
                g.setColor(Color.red);
                int width = (int) Math.abs(b.getX() - a.getX());
                int h = (int) Math.abs(b.getY() - a.getY());
                g.drawOval((int) a.getX(), (int) a.getY(), width, h);
            }
        }
    }

}

在你走得更远之前，你真的应该通读......

如果你继续遵循目前的做法，你会有一些非常讨厌的事情。

此外，阅读How to Write a Mouse Listener

也不会有什么坏处

答案 1 :(得分：3)

您的课程有mouseClicked()，mouseReleased()等方法，但它没有实现MouseListener。即使它是，它也从未作为MouseListener添加到任何组件。

所以，让你的类实现MouseListener：

public class MouseEvtEx2 extends JFrame implements MouseListener {

并将自身添加为要侦听的组件的鼠标侦听器：

panelTop.addMouseListener(this);

当然，为了帮助您自己阅读和理解您自己的代码，请将其缩进。

答案 2 :(得分：2)

我做了一些改动让它发挥作用。您需要在implement MouseListener框架上MouseEvtEx2，并且还需要将其作为MouseListener添加到panel p1 

public class MouseEvtEx2 extends JFrame implements MouseListener {
    private JTextArea txtArea;

    public MouseEvtEx2(String title) {
        super(title);
        Panel p1 = new Panel();
        MyPanel panelTop = new MyPanel();
        panelTop.setBackground(new Color(0.98f, 0.97f, 0.85f));
        panelTop.setOpaque(true);
        panelTop.setPreferredSize(new Dimension(400, 200));
        panelTop.setBorder(BorderFactory.createRaisedBevelBorder());

        getContentPane().add(panelTop);
        txtArea = new JTextArea();
        txtArea.setEditable(false);
        JScrollPane pane = new JScrollPane(txtArea);
        pane.setPreferredSize(new Dimension(400, 200));
        p1.setLayout(new GridLayout(2, 1, 0, 0));
        getContentPane().add(p1);
        p1.addMouseListener(this);
        p1.add(pane);

        // txtArea.setText
        // revalidate();
        setSize(600, 600);
        show();
    }

    public void record(String st, MouseEvent et) {
        txtArea.setText("" + st + "" + et.toString());
    }// setVisible(true);}

    public void mouseClicked(MouseEvent evt) {
        record("Mouse clicked # of mouse clicks: " + evt.getClickCount(), evt);// +
                                                                                // " "
                                                                                // +

    }

    public void mouseEntered(MouseEvent evt) {
        record("Mouse entered ", evt);// .toString());
    }

    public void mouseExited(MouseEvent evt) {
        record("Mouse exited ", evt);// .toString());
    }

    public void mousePressed(MouseEvent evt) {
        record("Mouse pressed # of mouse clicks: ", evt);// .getClickCount() +
                                                            // " " +

    }

    public void mouseReleased(MouseEvent evt) {
        record("Mouse released ", evt);
    }

    public static void main(String[] args) {
        new MouseEvtEx2("Mouse events");
    }
}

希望这有帮助。

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