Question

过去一天半我一直在搜索谷歌，试图解决这个问题。正如您所看到的，我正在尝试使用mouseClicked更新变量clickcolumnindex和clickrowindex，以便在mouseClicked方法更新中生成replaint（）方法，从而显示由另一列/行中的绘画显示创建的计数器。

我觉得这可能是一个非常简单的解决方法，在我尝试了很多东西之后，我有点失去了思路。

非常感谢帮助。

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

            class GridPanel extends JPanel implements MouseListener
            {
                int numCols;
                int numRows;
                int w;
                int h;
                int x;
                int y;
                int clickcolumnindex;
                int clickrowindex;


                public void mouseReleased(MouseEvent event)
                {
                    System.out.println("Mouse released.");
                }
                public void mousePressed(MouseEvent event)
                {
                    System.out.println("Mouse Pressed");
                }
                public void mouseClicked(MouseEvent event)
                {
                    int clickcolumnindex = 7 * x / getWidth();
                    int clickrowindex = 5 * y / getHeight();
                    int x = event.getX();
                    int y = event.getY();
                    System.out.println("x position of click is: " +x);
                    System.out.println("y position of click is: " +y);
                    System.out.println("Click is in column " +clickcolumnindex);
                    System.out.println("Click is in row " +clickrowindex);
                    repaint();

                }


   public void mouseReleased(MouseEvent event) {
      System.out.println("Mouse released.");
   }

   public void mousePressed(MouseEvent event) {
      System.out.println("Mouse Pressed");
   }

   public void mouseClicked(MouseEvent event) {
      int x = event.getX();
      int y = event.getY();
      System.out.println("x position of click is: " + x);
      System.out.println("y position of click is: " + y);
      System.out.println("Click is in column " + clickcolumnindex);
      System.out.println("Click is in row " + clickrowindex);
      repaint();
   }

   public void mouseEntered(MouseEvent event) {
      System.out.println("Mouse entered.");
   }

   public void mouseExited(MouseEvent event) {
      System.out.println("Mouse exited.");
   }

   public GridPanel(int nc, int nr) {
      numCols = nc;
      numRows = nr;
      addMouseListener(this);
   }

   Rectangle getRect(int thisCol, int thisRow) {
      // if input is out of range, return "null"
      if (thisCol < 0 || thisRow < 0)
         return null;
      if (thisCol >= numCols || thisRow >= numRows)
         return null;
      // otherwise, make and return the Rectangle
      int w = getWidth() / numCols;
      int h = getHeight() / numRows;
      int x = thisCol * w;
      int y = thisRow * h;
      Rectangle myRect = new Rectangle(x, y, w, h);
      return myRect;
   }

   public void paint(Graphics g) {
      g.setColor(Color.gray);
      g.fillRect(0, 0, getWidth(), getHeight());
      g.setColor(Color.black);
      Graphics2D g2 = (Graphics2D) g;
      // we'll use Graphics2D for it's "draw" method -
      // neater than the Graphics "drawRect" suppled
      // (which you could also use)
      for (int i = 0; i < numCols; i++) {
         for (int j = 0; j < numRows; j++) {
            Rectangle r = getRect(i, j);
            g2.draw(r);
         }
      }
      g2.setColor(Color.blue);
      Rectangle r1 = getRect(clickcolumnindex, clickrowindex);
      g2.fillOval(r1.x, r1.y, r1.width, r1.height);
      System.out.println("variable updates " + clickcolumnindex + clickrowindex);
   }

   // copied from the W2MouseEvents for convenience
   // (so we can run the program from GridPanel class too!)
   public static void main(String[] args) {
      W2MouseEvents w = new W2MouseEvents();
      w.setVisible(true);
   }
}

W2MouseEvents.java：

import javax.swing.JFrame;

public class W2MouseEvents extends JFrame {
   GridPanel myGridPanel;

   public static void main(String[] args) {
      W2MouseEvents w = new W2MouseEvents();
      w.setVisible(true);
   }

   public W2MouseEvents() {
      setTitle("Workshop 2 (Mouse Events): starting code");
      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setSize(500, 400);
      setLocation(300, 300);
      myGridPanel = new GridPanel(7, 5);
      add(myGridPanel);
   }

}

Answer 1

至少有两个问题：变量不会神奇地自动更新。如果更改了x，则右侧没有变量（假设它们在同一范围内）的变量不会更新。澄清：

假设您想要全局更改int x = 4; int var = x + 1; // var == 5 x = 5 // var still is 5, not 6和x“（如”班级实例的属性“），您需要解决的第二个问题是

这里发生的是你宣布两个新的本地变量public void mouseClicked(MouseEvent event) { int x = event.getX(); int y = event.getY(); // ... }和x，但无论你赋予它们什么价值，你的“全局”变量y并且x不会改变除非你遗漏声明y。如果您在其中一个mouseClicked / mousePressed / ...方法中重新计算 int和clickColumnIndex的值，则不会出现此问题。

修改我看到你已将clickRowIndex及其兄弟的计算移至clickColumnIndex方法。但如上所述，您正在创建两个新变量，隐藏“全局”变量。只需删除mouseClicked。
即可

Answer 2

在声明鼠标事件之前，您可以设置clickcolumnindex。您需要在鼠标侦听器中设置它。

换句话说，这是毫无意义的：

        class GridPanel extends JPanel implements MouseListener
        {
            int numCols;
            int numRows;
            int w;
            int h;
            int x;
            int y;
            int clickcolumnindex = 7 * x / getWidth();
            int clickrowindex = 5 * y / getHeight();

因为此时x是0，所以getWidth（）（这里没有得到除零的错误）。

您想要在MouseListener的mousePressed(...)方法中设置clickXXXindex。我更喜欢使用mousePressed(...)而不是mouseClicked(...)，因为前者在按下鼠标后移动鼠标并不是那么挑剔。

此外，您还希望在JPanel的paintComponent(...)方法中进行绘制，而不是paint(...)方法。

Answer 3

陈述：

   int clickcolumnindex = 7 * x / getWidth();
   int clickrowindex = 5 * y / getHeight();

不允许在构造函数，方法或静态初始化程序块之外。

正如HoverMeister所指出的那样，这些只会被分配一次。为什么不使用单独的方法来更新这些变量和后续的repaint（）？

变量不会传递给方法绘制

3 个答案: