Question

我正在开发一个简单的应用程序Java / Swing，它涉及让用户点击一个框并拖动它。我很难理解如何使用重绘方法。我创建了这个问题的例子，其中绘制了一个正方形，然后在mousePressed上获得了点击的x坐标，并且移动指针移动了原始绘图。

我已经阅读了Swing中关于绘图的常用指南，但我还没有看到关于如何编写包含mouseMotion和mouseListener的程序的问题的任何答案（据我所知，这意味着mouseListener必须实现为自己的类，而不是将其合并到自定义JPanel类中的常见解决方案，并且还基于鼠标操作调用repaint()。

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


class drawTest extends JPanel {
    static int xpos_square = 200; 
    static int ypos_square = 200; 
    int width = 100;  
    int height = 100;

    static int x_init;
    static int y_init;

    public drawTest(){
        addMouseListener(new mouseListener());
        addMouseMotionListener(new mouseListener());
        setBackground(Color.BLACK); 
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        drawSquare(g);
    }

    public void drawSquare(Graphics g){
        g.setColor(Color.GREEN);
        g.fillRect(xpos_square, ypos_square, height, width);            
    }   

    public static void moveShape(int x, int y){
        xpos_square += x-x_init;
        ypos_square += y-y_init;
        repaint();
    }
    public static void getChord(int x, int y){
        x_init = x;
        y_init = y;     
    }
}   

class mouseListener extends MouseInputAdapter{

    public void mousePressed(MouseEvent e){     
        drawTest.getChord(e.getX(),e.getY());
    }   

    public void mouseDragged(MouseEvent e){
        drawTest.moveShape(e.getX(),e.getY());
    }       
}

public class myTest {

    JFrame myFrame = new JFrame();
    JPanel myDrawing = new drawTest();

    public myTest () {
        myFrame.add(myDrawing);
        myFrame.setSize(500,500);
        myFrame.setVisible(true);
        myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }   

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

问题当然是repaint()无法在静态上下文中调用。但是，我不知道如何避免这种情况，因为如果我想要平稳地更新位置，则必须通过mouseDragged方法调用它。

我怎样才能使用repaint()方法根据鼠标移动重绘？

Answer 1

所以我在addMouseListener中使用匿名方法找到了解决方法。这绕过了重绘调用中对静态方法的需求。如果其他人有类似的问题，也许他们会发现它有用。

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


class DrawTest extends JPanel {
    static int xpos_square = 200; 
    static int ypos_square = 200; 
    int width = 100;  
    int height = 100;

    static int x_init;
    static int y_init;

    public DrawTest(){
        addMouseListener(new mouseListener(){   public void mousePressed(MouseEvent e){     
            getClick(e.getX(),e.getY());
        }});
        addMouseMotionListener(new mouseListener(){ public void mouseDragged(MouseEvent e){
            moveShape(e.getX(),e.getY());   
        }});
        setBackground(Color.BLACK); 
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        drawSquare(g);
    }

    public void drawSquare(Graphics g){
        g.setColor(Color.GREEN);
        g.fillRect(xpos_square, ypos_square, height, width);            
    }   

    public void moveShape(int x, int y){
        if((x >= xpos_square)&&(x <= xpos_square + width)&&(y >= ypos_square)&&(y <= ypos_square + height)){
            xpos_square += x-x_init;
            ypos_square += y-y_init;
            x_init = x;
            y_init = y; 
            repaint();
        }
    }
    public void getClick(int x, int y){
        x_init = x;
        y_init = y;     
    }
}

public class MyTest {

    JFrame myFrame = new JFrame();
    JPanel myDrawing = new DrawTest();

    public MyTest () {
        myFrame.add(myDrawing);
        myFrame.setSize(500,500);
        myFrame.setVisible(true);
        myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }   

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

Java：在静态上下文中调用repaint（）（或者如何避免它）

1 个答案: