如何實時激發MouseMotionListener事件？

Question

我正在嘗試創建一個圖形繪製程序，允許用戶通過將鼠標拖到屏幕上來繪製紅色像素。所以從某種意義上說，你可以把這個程序想象成微軟的畫圖程序，但只有鉛筆繪畫工具和紅色。

不幸的是，我的程序中的mouseDragged()函數無法正常工作。它會跳過一些像素的屏幕上，如果我將我的鼠標速度太快，就像這樣：

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

public class FrameView extends JFrame { 
    JPanel panel; 
    Graphics2D drawingContext; 

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

    public FrameView() { 
     panel = new JPanel(); 
     panel.addMouseMotionListener(new MouseControls()); 
     panel.setBackground(Color.WHITE); 
     this.add(panel); 
     this.setSize(new Dimension(500, 500)); 
     this.setTitle("Drawing Program"); 
     this.setVisible(true); 
     drawingContext = (Graphics2D)panel.getGraphics(); 
    } 

    private class MouseControls extends MouseAdapter { 
     @Override 
     public void mouseDragged(MouseEvent e) { 
      int x = e.getX(); 
      int y = e.getY(); 

      final int WIDTH = 1; 
      final int HEIGHT = 1; 
      Shape pixel = new Rectangle(x, y, WIDTH, HEIGHT); 
      drawingContext.setColor(Color.RED); 
      drawingContext.draw(pixel); 
     } 
    } 
} 

Answer 1

getGraphics不是如何在Swing繪畫作品，相反，你應該重寫paintComponent組件的方法並在那裏執行自定義繪畫。

繪畫具有破壞性，預計當調用paintComponent時，將完全重新繪製組件的當前狀態。

看一看Painting in AWT and Swing和Performing Custom Painting更多細節

至於你的「鼠標」的問題，這實際上是如何工作的，你就不會被通知每一個像素位置上的鼠標必須通過的，如果有的話，你的鼠標在屏幕上會出現可怕的差距。相反，操作系統會根據用戶輸入的移動速度以不斷增加的步幅移動鼠標。

代替繪圖的只是點，畫出它們之間的線路，例如

注：我故意畫大點，所以你可以看到他們是被報道在那裏，你會看到所有的點（對於單拖）連接

import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.EventQueue; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.Point; 
import java.awt.event.MouseAdapter; 
import java.awt.event.MouseEvent; 
import java.awt.geom.Ellipse2D; 
import java.awt.geom.Line2D; 
import java.util.ArrayList; 
import java.util.List; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.UIManager; 
import javax.swing.UnsupportedLookAndFeelException; 

public class Test { 

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

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

       JFrame frame = new JFrame("Testing"); 
       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
       frame.add(new TestPane()); 
       frame.pack(); 
       frame.setLocationRelativeTo(null); 
       frame.setVisible(true); 
      } 
     }); 
    } 

    public class TestPane extends JPanel { 

     private List<List<Point>> points = new ArrayList<>(25); 
     private List<Point> activeList; 

     public TestPane() { 
      MouseAdapter ma = new MouseAdapter() { 
       @Override 
       public void mouseDragged(MouseEvent e) { 

        if (activeList != null) { 
         activeList.add(e.getPoint()); 
         repaint(); 
        } 
       } 

       @Override 
       public void mousePressed(MouseEvent e) { 
        activeList = new ArrayList<>(25); 
        points.add(activeList); 
       } 

       @Override 
       public void mouseReleased(MouseEvent e) { 
        if (activeList != null && activeList.isEmpty()) { 
         points.remove(activeList); 
        } 
        activeList = null; 
       } 

      }; 
      addMouseMotionListener(ma); 
      addMouseListener(ma); 
     } 

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

     @Override 
     protected void paintComponent(Graphics g) { 
      super.paintComponent(g); 
      Graphics2D g2d = (Graphics2D) g.create(); 
      g2d.setColor(Color.RED); 
      for (List<Point> group : points) { 
       Point previous = null; 
       for (Point p : group) { 
        // You can get rid of this, it's simply to show 
        // where the points would actually be rendered 
        g2d.fill(new Ellipse2D.Float(p.x - 2, p.y - 2, 4, 4)); 
        if (previous != null) { 
         g2d.draw(new Line2D.Float(previous, p)); 
        } 
        previous = p; 
       } 
      } 
      g2d.dispose(); 
     } 

    } 

}