我有一个程序,应该根据用户单击的按钮在屏幕上放置咖啡杯的图像,但是我的图像并不总是显示,而且当显示时,它也不会移动。有人可以帮我找出我的代码哪里不正确吗?谢谢!
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class MoveIt extends Applet implements ActionListener
{
//Declare Variables
private Image cup;
private Panel keyPad;
public int top = 15;
public int left = 15;
private boolean foundKey;
public void init()
{
cup = getImage(getDocumentBase(), "cup.gif");
Canvas myCanvas = new Canvas();
keyPad = new Panel();
keysArray = new Button[5];
//Create Buttons
keysArray[0] = new Button("Up");
keysArray[1] = new Button("Left");
keysArray[2] = new Button("Right");
keysArray[3] = new Button("Down");
keysArray[4] = new Button("Center");
keysArray[0].setActionCommand("Up");
keysArray[1].setActionCommand("Left");
keysArray[2].setActionCommand("Right");
keysArray[3].setActionCommand("Down");
keysArray[4].setActionCommand("Center");
setBackground(Color.blue);
//Sets the layout manager for the frame
setLayout(new BorderLayout());
//Sets the layout manager for the Panel
keyPad.setLayout(new BorderLayout());
//Add Buttons to keypad panel
keyPad.add(keysArray[0], BorderLayout.NORTH);
keyPad.add(keysArray[1], BorderLayout.WEST);
keyPad.add(keysArray[2], BorderLayout.EAST);
keyPad.add(keysArray[3], BorderLayout.SOUTH);
keyPad.add(keysArray[4], BorderLayout.CENTER);
add(myCanvas, BorderLayout.NORTH);
add(keyPad, BorderLayout.SOUTH);
//adds actionlistener to the buttons
for(int i = 0; i < keysArray.length; i++)
keysArray[i].addActionListener(this);
}
//puts image on the canvas
public void paint( Graphics g )
{
g.drawImage( cup, left, top, this );
}
public void actionPerformed(ActionEvent e)
{
String arg = e.getActionCommand();
if(arg == "Up") top = top - 15;
if(arg == "Left") left = left - 15;
if(arg == "Right") left = left + 15;
if(arg == "Down") top = top + 15;
if(arg == "Center")
{
top = 60;
left = 125;
}
repaint();
}
}
最佳答案
这有很多问题,但让我们从根本原因开始......
这个 if (arg == "Up") {
并不是 Java 中 String
比较的工作方式。相反,您应该使用 "Up".equals(arg)
或者如果您不关心大小写 "Up".equalsIgnoreCase(arg)
用户一次按下多个按钮的可能性也很小,因此,而不是
if ("Up".equals(arg)) {...}
if ("Left".equals(arg)) {...}
您应该使用 if-else
语句
if ("Up".equals(arg)) {
//...
} else if ("Left".equals(arg)) {
//..
} ...
已更新
我要推荐的一些内容已经由 rendon 开始讨论,所以给他 +1。
- (个人)避免使用 AWT 并使用 Swing。大约 13 年前,AWT 被 Swing 取代
- 避免直接绘制到顶层容器。这些容器的顶部通常有很多层,直接在它们上绘画可能会弄乱它们。相反,创建一个容器(如
JPanel
并在其上构建您的应用程序)。这将使其在未来更加便携和可重复使用 - 您必须调用
super.paintXxx
,除非您有非常非常充分的理由不调用,并且准备好处理这些方法所做的所有工作。 - 避免“神奇”数字。相反,依赖绝对值。在本例中,是要绘制的容器的宽度和高度以及图像的大小。这将确保“center”实际上是“center”
以下示例演示了其中一些想法。基本上,我创建了一个 ControlPane
Pane ,其中包含按钮和 CupPane
。 CupPane
是独立的,负责绘制和定位杯子
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JApplet;
import javax.swing.JButton;
import javax.swing.JPanel;
public class MoveIt extends JApplet {
public void init() {
setLayout(new BorderLayout());
add(new ControlPane());
}
public class CupPane extends JPanel {
private Image cup;
public int top = 15;
public int left = 15;
public CupPane() {
cup = getImage(getDocumentBase(), "cup.png");
setBackground(Color.BLUE);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(cup, left, top, this);
}
public void moveUp() {
top -= 15;
repaint();
}
public void moveLeft() {
left -= 15;
repaint();
}
public void moveRight() {
left += 15;
repaint();
}
public void moveDown() {
top += 15;
repaint();
}
public void center() {
int width = getWidth();
int height = getHeight();
top = (height - cup.getHeight(this)) / 2;
left = (width - cup.getWidth(this)) / 2;
}
}
public class ControlPane extends JPanel {
private JPanel keyPad;
public int top = 15;
public int left = 15;
private boolean foundKey;
private JButton[] keysArray;
private CupPane cupPane;
public ControlPane() {
keyPad = new JPanel();
keysArray = new JButton[5];
cupPane = new CupPane();
//Create Buttons
keysArray[0] = new JButton("Up");
keysArray[1] = new JButton("Left");
keysArray[2] = new JButton("Right");
keysArray[3] = new JButton("Down");
keysArray[4] = new JButton("Center");
keysArray[0].setActionCommand("Up");
keysArray[1].setActionCommand("Left");
keysArray[2].setActionCommand("Right");
keysArray[3].setActionCommand("Down");
keysArray[4].setActionCommand("Center");
setBackground(Color.blue);
//Sets the layout manager for the frame
setLayout(new BorderLayout());
//Sets the layout manager for the Panel
keyPad.setLayout(new BorderLayout());
//Add Buttons to keypad panel
keyPad.add(keysArray[0], BorderLayout.NORTH);
keyPad.add(keysArray[1], BorderLayout.WEST);
keyPad.add(keysArray[2], BorderLayout.EAST);
keyPad.add(keysArray[3], BorderLayout.SOUTH);
keyPad.add(keysArray[4], BorderLayout.CENTER);
add(cupPane, BorderLayout.CENTER);
add(keyPad, BorderLayout.SOUTH);
ActionHandler handler = new ActionHandler();
//adds actionlistener to the buttons
for (int i = 0; i < keysArray.length; i++) {
keysArray[i].addActionListener(handler);
}
}
protected class ActionHandler implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
String arg = e.getActionCommand();
if ("Up".equals(arg)) {
cupPane.moveUp();
} else if ("Left".equals(arg)) {
cupPane.moveLeft();
} else if ("Right".equals(arg)) {
cupPane.moveRight();
} else if ("Down".equals(arg)) {
cupPane.moveDown();
} else if ("Center".equals(arg)) {
cupPane.center();
}
repaint();
}
}
}
}
您可能想看看Performing Custom Painting和 Painting in AWT and Swing了解更多详情
关于java - 图形未显示在可点击界面上,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/17821548/