Question

我从学习资源中获取了以下代码。当我运行applet时，我注意到'Up'仅在拖动鼠标后显示。如果按下鼠标按钮然后在同一位置释放，则不会显示“向上”。为什么在后一种情况下不显示'Up'？

// Demonstrate the mouse event handlers. 
import java.awt.*; 
import java.awt.event.*; 
import java.applet.*; 
/* 
  <applet code="MouseEvents" width=300 height=100> 
  </applet> 
*/ 

public class MouseEvents extends Applet 
  implements MouseListener, MouseMotionListener { 

  String msg = ""; 
  int mouseX = 0, mouseY = 0; // coordinates of mouse 

  public void init() { 
     addMouseListener(this); 
     addMouseMotionListener(this); 
  } 

  // Handle mouse clicked. 
  public void mouseClicked(MouseEvent mld) { 
    mouseX = 0; 
    mouseY = 20; 
    msg = "Mouse clicked."; 
    repaint(); 
  } 

  // Handle mouse entered. 
  public void mouseEntered(MouseEvent mld) { 
    mouseX = 0; 
    mouseY = 30; 
    msg = "Mouse entered."; 
    repaint(); 
  } 

  // Handle mouse exited. 
  public void mouseExited(MouseEvent mld) { 
    mouseX = 0; 
    mouseY = 10; 
    msg = "Mouse exited."; 
    repaint(); 
  } 

  // Handle button pressed. 
  public void mousePressed(MouseEvent mld) { 
    // save coordinates 
    mouseX = mld.getX(); 
    mouseY = mld.getY(); 
    msg = "Down"; 
    repaint(); 
  } 

  // Handle button released. 
  public void mouseReleased(MouseEvent mld) { 
    // save coordinates 
    mouseX = mld.getX(); 
    mouseY = mld.getY(); 
    msg = "Up"; 
    repaint(); 
  } 

  // Handle mouse dragged. 
  public void mouseDragged(MouseEvent mld) { 
    // save coordinates 
    mouseX = mld.getX(); 
    mouseY = mld.getY(); 
    msg = "*"; 
    showStatus("Dragging mouse at " + mouseX + ", " + mouseY); 
    repaint(); 
  } 

  // Handle mouse moved. 
  public void mouseMoved(MouseEvent mld) { 
    // show status 
    showStatus("Moving mouse at " + mld.getX() + ", " + mld.getY()); 
  } 

  // Display msg in applet window at current X,Y location. 
  public void paint(Graphics g) { 
    g.drawString(msg, mouseX, mouseY); 
  } 
}

Answer 1

拖动时mouseClicked将不会被调用，但mouseReleased将被调用。在单个位置点击后，mouseReleased后跟mouseClicked，因此被点击的活动会覆盖已发布的内容

尝试将System.out.println语句添加到MouseListener方法中并跟踪控制台中的输出...

// Handle mouse clicked. 
public void mouseClicked(MouseEvent mld) {
    mouseX = 0;
    mouseY = 20;
    msg = "Mouse clicked.";
    System.out.println("clicked");
    repaint();
}

// Handle button pressed. 
public void mousePressed(MouseEvent mld) {
    // save coordinates 
    mouseX = mld.getX();
    mouseY = mld.getY();
    msg = "Down";
    System.out.println("down");
    repaint();
}

// Handle button released. 
public void mouseReleased(MouseEvent mld) {
    // save coordinates 
    mouseX = mld.getX();
    mouseY = mld.getY();
    msg = "Up";
    System.out.println("up");
    repaint();
}

// Handle mouse dragged. 
public void mouseDragged(MouseEvent mld) {
    // save coordinates 
    mouseX = mld.getX();
    mouseY = mld.getY();
    msg = "*";
    showStatus("Dragging mouse at " + mouseX + ", " + mouseY);
    System.out.println("dragged");
    repaint();
}

// Handle mouse dragged. 
public void mouseDragged(MouseEvent mld) {
    // save coordinates 
    mouseX = mld.getX();
    mouseY = mld.getY();
    msg = "*";
    showStatus("Dragging mouse at " + mouseX + ", " + mouseY);
    System.out.println("dragged");
    repaint();
}

你应该看到......

down
up
clicked

单击一个点，但

down
dragged
.
.
.
up

被拖动

Java mouseReleased（）方法查询

1 个答案: