使用带有actionPerformed的repaint（）方法

Question

如何在按下按钮时使用repaint（）方法并且Graphics p必须从头开始重新绘制所有内容？

感谢。

  import javax.swing.Box;
  import javax.swing.JButton;
  import javax.swing.JTextField;
  import java.awt.*;
  import java.awt.event.*;
  import javax.swing.*;

  class fares extends JPanel{

    private static final long serialVersionUID = 1L;
    public static int xaxis1,xaxis2,yaxis3,yaxis4;

public ControlsB(square) {

    final JButton btn1 = new JButton("Resize");

    final Box b = Box.createHorizontalBox();
    b.add(new JLabel("Please enter range:  "));
    Box b0 = Box.createVerticalBox();//create a vertical box to stack the controls

    Box b1 = Box.createHorizontalBox(); // create a horizontal box for the x-axis

    //x-axis
    b1.add(new JLabel("mark "));
    b1.add(new JLabel("for"));

    f1.setMaximumSize(new Dimension(100,30));

    b1.add(f1);
    b1.add(new JLabel("till"));

    f2.setMaximumSize(new Dimension(100,30));
    b1.add(f2);

    //y-axis
    //this code is not in use at the moment

    f4.setMaximumSize(new Dimension(100,30));
    b2.add(f4);

    b0.add(b1);

    add(b);

    btn1.addActionListener(new ActionListener(){

        public void actionPerformed(ActionEvent event){

            f = Integer.parseInt(f1.getText());

            invalidate();
            validate();
            paint(p);//this is not working...
        }
    });
 b.add(btn1);
  }
}

这是必须调用并重新绘制的代码：

import java.awt.*;

import javax.swing.*;

class Graph extends JPanel {

public static Graphics p;
private static final long serialVersionUID = 1L;
public static int f;
public static int g;

@Override
public Dimension getPreferredSize()
{   
    return (new Dimension(560,560));
}

public void paintComponent(Graphics p) {

    super.paintComponent(p);

    Graphics2D graph = (Graphics2D)p;

    Dimension appletSize = this.getSize();
    int appletHeight = (int)(appletSize.height);
    int appletWidth = appletSize.width;

    //change -ve num to +ve
    int g3 = Math.abs(g);

    int a1 = g3 + f;
    int b1 = a1;


    int d = (appletWidth / a1);
    int e = (appletHeight / b1);

    //draw y-axis numbers 
    //(+ve)
    while(f != 0){
        String s = String.valueOf(f);

        m = m + b;
        f = f - 1;
    }
    //(-ve)
    m2 = y;
    while(f2 != g-1)
        m2 = m2 + b;
        f2 = f2 - 1;
    }
    //draw x-axis numbers.
    //(-ve)
    while(g != 0){
        String hy = String.valueOf(g);

        n = n + a;
        g = g + 1;
    }
    //(+ve)
    n2 = x + a;
    while(g2 != g3+1){
        String w = String.valueOf(g2);
        n2 = n2 + a;
        g2 = g2 + 1;
    }

    BasicStroke aLine2 = new BasicStroke(1.0F,
                                         BasicStroke.CAP_ROUND,BasicStroke.JOIN_ROUND);
    graph.setStroke(aLine2);

    //notch on numbers and grid lines
    //left to right, top to bottom notches
    int v2 = -5;
    int v5 = 0;
    while(i <= a1-1){
        p.setColor(Color.lightGray);//lightgray line
        a = a + d;
        b = b + e;
        i = i + 1;
    }

  }
}

当调整大小按钮工作时，我需要调整窗口大小以使图形响应给定的输入。基本上，当重新调整图形的大小/重新绘制时...现在我需要自动完成。

Answer 1

基于代码片段很难分辨出什么是错误的，但看起来您的图形是在Graph对象上绘制的，称为图形（如果我错了请纠正我），并且您似乎正在尝试重新绘制（或油漆 - 永远不要直接调用！）您的ControlsB面板。如果是这样，那么您可能正在调用错误对象上的方法。也许你需要做一些事情：

// graph is final so it may be used in an inner class
public ControlsB(Box box2, final Graph graph) {

     // .....

      btn1.addActionListener(new ActionListener(){

        public void actionPerformed(ActionEvent event){

            f = Integer.parseInt(f1.getText());
            g = Integer.parseInt(f2.getText());
            System.out.println(f + "  " + g);

            // invalidate();
            // validate();
            //  paint(p); ***** NEVER do this

            graph.repaint();
        }
    });
}

此外：

• 除非在非常特殊的情况下（不是这样），否则不要直接在组件上调用paint(...)。
• 永远不要试图抓住组件Graphics对象并使用它进行绘制，因为这通常会导致NullPointerException发生，并且肯定无法正常工作。
• 请阅读标准Swing教程中如何在Swing中进行绘图。你可能会从这方面学到很多东西。
• 同样，如果您很快得不到合适的答案，请考虑创建并发布sscce。

Answer 2

所做的更改：

- 在GraphApplet类中，这两行已更改

Box box2 = new Box(BoxLayout.Y_AXIS); // Changed
// Added one more argument, while making Object.
ControlsB b = new ControlsB(box2, graph);//horizontal

• 内部图表类，已添加setValues(...)方法。

-

public void setValues(int x, int y)
{
    xstart = x;
    ystart = y;
    repaint();
}

• 在Graph类内，变量范围xstart和ystart具有 已更改为Instance/Class

- 内部ControlB类

refineButton = new JButton("Refine");
buttonBox.add(refineButton);
refineButton.addActionListener(new ActionListener()
{
    public void actionPerformed(ActionEvent ae)
    {
        int x = Integer.parseInt(f1.getText());
        int y = Integer.parseInt(f3.getText());
        /*
         * Calling a method of Graph Class (setValues)
         * and passing the values that we had got from
         * the respective JTextFields.
         */
        graph.setValues(x, y);          }
    });
}

在这里观看这段代码示例，稍微修改了您之前的示例，以便您了解如何使其工作。看看附加的图像，只使用这三个东西，在指向JTextField s中输入一些整数值，然后点击Refine JButton，你会看到如何重绘。由于我真的不知道逻辑是如何工作的，因此无法说出如何优化代码，虽然给你一个想法，这里是：

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;

public class GraphApplet extends JApplet
{
    private static final long serialVersionUID = 1L;

    public void init(){

        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                Container conn = getContentPane();
                conn.setLayout(new BorderLayout());

                Graph graph = new Graph();//graph
                conn.add(graph,BorderLayout.CENTER);

                Box box1 = new Box(BoxLayout.X_AXIS);
                ControlsA a = new ControlsA(box1);//vertical
                conn.add(a,BorderLayout.EAST);

                Box box2 = new Box(BoxLayout.Y_AXIS); // Changed
                // Added one more argument, while making Object.
                ControlsB b = new ControlsB(box2, graph);//horizontal
                conn.add(b,BorderLayout.SOUTH);
            }
        });
    }
}

class Graph extends JPanel {

    private static final long serialVersionUID = 1L;
    private int xstart;
    private int ystart;

    public Graph(){
        this.setBackground(Color.yellow);
    }

    @Override
    public Dimension getPreferredSize()
    {   
        return (new Dimension(460,560));
    }

    /*
     * Added this method, which will call
     * repaint(), everytime it is been
     * called from anywhere. Moreover
     * the variables used inside 
     * paintComponent(...) method xstart
     * and ystart, have been changed to 
     * instance variables of the Graph Class.
     */
    public void setValues(int x, int y)
    {
        xstart = x;
        ystart = y;
        repaint();
    }

    @Override
    public void paintComponent(Graphics p) 
    {

        super.paintComponent(p);

        Graphics2D graph = (Graphics2D)p;

        Dimension appletSize = this.getSize();
        int appletHeight = (int)(appletSize.height);
        int appletWidth = appletSize.width;

        this.setBackground(Color.yellow);//set background color.

        int x,y,y1,x1,a,b,p1x,p1y,p2x,p2y;

        //line co-ordinates
        //the numbers represent the number of boxes on the graph
        // Made these two variables as Instance Variables
        //int xstart = 10;
        //int ystart = 5;

        int xfinish = 2;
        int yfinish = 8;

        //other variables
        int i = 0;
        int i2 = 0;
        int m = 0;
        int n = 0;
        int m2 = 0;
        int n2 = 0;
        int f2 = 0;
        int g2 = 1;

        //ranges
        int f = 5;
        int g = -5;

        //change -ve num to +ve
        int g3 = Math.abs(g);

        int a1 = g3 + f;
        int b1 = a1;

        y1 = (appletHeight);
        x1 = (appletWidth);
        y = (appletHeight / 2);
        x = (appletWidth / 2);
        a = (appletWidth / a1);
        b = (appletHeight / b1);

        int d = (appletWidth / a1);
        int e = (appletHeight / b1);

        /**
        to determine the
        ammount of pixles there
        is in each box of the
        graph, both y-axis and 
        x-axis
        */
        int xbox = x1 / 10;
        int ybox = y1 / 10;

        //line variables
        //the xstart, ystart, etc represent the number of boxes

        //top point of the line on the graph
        p1x = xbox * xstart;//start x
        p1y = ybox * ystart;//start y

        //lowwer point of the line on the graph
        p2x = xbox * xfinish;//finish x
        p2y = ybox * yfinish;//finish y

        //draw y-axis numbers 
        //(+ve)
        while(f != 0){
            String s = String.valueOf(f);
            p.drawString(s,(x + 5),m + 13);
            m = m + b;
            f = f - 1;
        }
        //(-ve)
        m2 = y;
        while(f2 != g-1){
            String u = String.valueOf(f2);
            p.drawString(u,(x + 5),m2 - 3);
            m2 = m2 + b;
            f2 = f2 - 1;
        }
        //draw x-axis numbers.
        //(-ve)
        while(g != 0){
            String t = String.valueOf(g);
            p.drawString(t,n,y - 5);
            n = n + a;
            g = g + 1;
        }
        //(+ve)
        n2 = x + a;
        while(g2 != g3+1){
            String vw = String.valueOf(g2);
            p.drawString(vw,n2 -10,y - 5);
            n2 = n2 + a;
            g2 = g2 + 1;
        }

        BasicStroke aLine2 = new BasicStroke(1.0F,
                 BasicStroke.CAP_ROUND,BasicStroke.JOIN_ROUND);
        graph.setStroke(aLine2);

        //notch on numbers and grid lines
        //left to right, top to bottom notches
        int v2 = -5;
        int v5 = 0;
        while(i <= a1-1){
            p.setColor(Color.lightGray);//lightgray line
            p.drawLine(a,0,a,y1);//vertical lightgray
            p.drawLine(0,b,x1,b);//horizontal lightgray
            a = a + d;
            b = b + e;
            i = i + 1;
        }
        //notches
        while(i2 <= a1){
            p.setColor(Color.blue);//notch color
            p.drawString("x",v2+2,y+3);//xaxis
                p.drawString("x",x-4,v5+4);//yaxis
            v5 = v5 + e;
            v2 = v2 + d;
            i2 = i2 + 1;
        }

        //draws the border of the graph
        p.setColor(Color.black);
        Rectangle2D.Float rect = new Rectangle2D.Float(0,0,x1,y1);
        BasicStroke aLine = new BasicStroke(2.5F, 
                BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND);
        graph.setStroke(aLine);
        graph.draw(rect);

        //draw cross
        BasicStroke aLine3 = new BasicStroke(2.5F,
                BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND);
        graph.setStroke(aLine3);
        p.drawLine(x,0,x,y1); //vertical line
        p.drawLine(0,y,x1,y); //horizontal line

        //display the value of graph width and graph height
        String aw = String.valueOf(x1);
        p.drawString("Graph Width = ", 50,90);
        p.drawString(aw,150,90);
        p.drawString("Graph Height = ", 50,110);
        String ah = String.valueOf(y1);
        p.drawString(ah,156,110);

        //draw line on graph

        BasicStroke aLine4 = new BasicStroke(1.5F,
            BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND);
        graph.setStroke(aLine4);
        p.setColor(Color.red);

        if(p1x <= x1 && p2x <= x1 && p1y <= y1 && p2y <= y1){
            p.drawLine(p1x,p1y,p2x,p2y);
            Color c = new Color(0,0,0);
            p.setColor(c);
            p.drawString("X", p1x-4,p1y+4);
            p.drawString("X", p2x-4,p2y+4);
        }           
        else{
            p.setColor(Color.black);
            p.drawRect(48,34,223,35);
            p.setColor(Color.white);
            p.fillRect(49,35,222,34);
            p.setColor(Color.red);
            p.drawString("Wrong co-ordinates!!!", 50,50);
            p.drawString("Values exceede applet dimensions.", 50,65);
        }
    }
}

class ControlsA extends JPanel
{

    private static final long serialVersionUID = 1L;

    public ControlsA (Box a) 
    {

        a = Box.createVerticalBox();
        a.add(new JLabel("Please enter the values below:"));
        a.add(new JLabel("a"));
        JTextField g1 = new JTextField("0.0");
        g1.setMaximumSize(new Dimension(100,30));
        a.add(g1);
        a.add(new JLabel("b"));
        JTextField g2 = new JTextField("0.0");
        g2.setMaximumSize(new Dimension(100,30));
        a.add(g2);
        a.add(new JLabel("c"));
        JTextField g3 = new JTextField("0.0");
        g3.setMaximumSize(new Dimension(100,30));
        a.add(g3);
        a.add(new JLabel("d"));
        JTextField g4 = new JTextField("0.0");
        g4.setMaximumSize(new Dimension(100,30));
        a.add(g4);
        a.add(new JButton("Plot"));
        a.add(new JButton("Refine"));
        add(a);
    }

    @Override
    public Dimension getPreferredSize()
    {   
        return (new Dimension(200,100));
    }
}

class ControlsB extends JPanel
{

    private static final long serialVersionUID = 1L;
    private Graph graph;
    private JButton refineButton;

    public ControlsB (Box b, Graph g) {

        graph = g;
        b = Box.createVerticalBox();
        Box boxUpper = new Box(BoxLayout.X_AXIS);
        boxUpper.add(new JLabel("Please enter range:  "));
        b.add(boxUpper);
        Box boxX = new Box(BoxLayout.X_AXIS);
        boxX.add(new JLabel(" x-axis "));
        boxX.add(new JLabel("from"));
        // Added final keyword.
        final JTextField f1 = new JTextField("-5");
        f1.setMaximumSize(new Dimension(100,30));
        boxX.add(f1);
        boxX.add(new JLabel(" to "));
        JTextField f2 = new JTextField("5");
        f2.setMaximumSize(new Dimension(100,30));
        boxX.add(f2);
        b.add(boxX);
        //b.add(new JLabel(".   "));
        Box boxY = new Box(BoxLayout.X_AXIS);
        boxY.add(new JLabel("y-axis "));
        boxY.add(new JLabel("from"));
        // Added final keyword.
        final JTextField f3 = new JTextField("5");
        f3.setMaximumSize(new Dimension(100,30));
        boxY.add(f3);
        boxY.add(new JLabel("to"));
        JTextField f4 = new JTextField("-5");
        f4.setMaximumSize(new Dimension(100,30));
        boxY.add(f4);
        b.add(boxY);
        Box buttonBox = new Box(BoxLayout.X_AXIS);
        buttonBox.add(new JButton("Plot"));
        /* 
         * Made this an instance variable,
         * and added ActionListener to it.
         */
        refineButton = new JButton("Refine");
        buttonBox.add(refineButton);
        refineButton.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent ae)
            {
                int x = Integer.parseInt(f1.getText());
                int y = Integer.parseInt(f3.getText());
                /*
                 * Calling a method of Graph Class (setValues)
                 * and passing the values that we had got from
                 * the respective JTextFields.
                 */
                graph.setValues(x, y);
            }
        });
        b.add(buttonBox);       
        add(b);
    }

    @Override
    public Dimension getPreferredSize()
    {   
        return (new Dimension(200,100));
    }
}

Answer 3

恭喜，你只是偶然发现了重绘的微妙之处:) http://www.oracle.com/technetwork/java/painting-140037.html#paint_process有一个很好的解释。以下是摘要：

• 如果你在JFrame或JApplet这样的重量级组件上调用repaint（），它会立即重新绘制。
• 如果你在一个JComponent上调用repaint（），它将“调度”重新绘制在将来的某个时刻发生，由重绘管理器决定（这意味着你无法控制它）。

因此，在JApplet中调用repaint（）方法，一旦单击按钮，就会看到更改。

Answer 4

您是否尝试过使用paint(p)或p.repaint()代替p.update(p.getGraphics())？

我没有做过多年的Swing，我也记不清它的表现如何。一个肯定的事情是你必须知道什么时候是调用paint，update或validate以及如何正确使用EventDispatcherThread（EDT）的好时机。否则你的应用程序将看起来像很多java swing应用程序：一堆填充的UI错误...

我不是说Swing是废话，我说如果你不知道它是如何工作的，那么你的用户界面将是一个垃圾。