我正在尝试将图像分配给网格布局，我发现堆栈溢出的解决方案。但是我已经改变了我的代码，现在它不工作，我得到的不能被抛出异常，我不知道为什么。
下面是抛出异常的方法，特别是imagePanel行：
public void setVehicle(int x, int y, Vehicle vehicle) {
this.vehicles[x][y] = vehicle;
ImageIcon image;
if (vehicle != null) {
image = vehicle.getImage();
} else {
image = null;
}
((ImagePanel) this.pnlCars.getComponent(x + (y - 1) * (this.vehicles.length - 1))).setImage(image);}
这是下面的图像面板类：
public class ImagePanel extends JPanel{
private ImageIcon image;
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (image != null) {
// Center icon
int width = this.getWidth();
int height = this.getHeight();
int iconWidth = image.getIconWidth();
int iconHeight = image.getIconHeight();
g.drawImage(image.getImage(), (width - iconWidth) / 2, (height - iconHeight) / 2, null);
}
}
public void setImage(ImageIcon image) {
this.image = image;
this.repaint();
}
}
这是错误信息：
Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: javax.swing.JPanel cannot be cast to carparkingprogram.gui.ImagePanel
at carparkingprogram.gui.CarParkPanel.setVehicle(CarParkPanel.java:197)
at carparkingprogram.gui.CarParkPanel$7$1.actionPerformed(CarParkPanel.java:325)
有人能帮忙吗？
这是完整的代码，显然我试图让它尽可能小，所以我只包括汽车部分。
public static int ROWS_LARGE = 1;
public static int ROWS_SMALL = 3;
public static int ROWS = ROWS_LARGE + ROWS_SMALL;
public static int COLUMNS = 4;
public Vehicle[][] vehicles = new Vehicle[ROWS][COLUMNS];
public CarParkPanel() {
this.setLayout(new BorderLayout());
pnlButtons = new JPanel();
pnlButtons.setLayout(null);
pnlButtons.setLayout(new BoxLayout(pnlButtons, BoxLayout.Y_AXIS));
pnlButtons.add(btnAddCar);
addCarMethod();
this.add(pnlButtons);
this.pnlLorry = new JPanel();
this.pnlLorry.setLayout(new GridLayout(ROWS_LARGE, COLUMNS));
this.pnlLorry.setPreferredSize(new Dimension(400, 200));
this.pnlCars = new JPanel();
this.pnlCars.setLayout(new GridLayout(ROWS_SMALL, COLUMNS));
this.pnlCars.setPreferredSize(new Dimension(400, 300));
//This is the code to create the grid panel that the images are added to
for (int row = 0; row < ROWS; row++) {
for (int column = 0; column < COLUMNS; column++) {
JPanel pnlVehicle = new JPanel(new BorderLayout());
pnlVehicle.setBorder(BorderFactory.createLineBorder(Color.RED));
pnlVehicle.addMouseListener(new MyMouseListener(column, (row * ROWS)));
if (row < ROWS_LARGE) {
this.pnlLorry.add(pnlVehicle);
} else {
this.pnlCars.add(pnlVehicle);
}
}
}
this.add(pnlButtons, BorderLayout.WEST);
this.pnlVehicles = new JPanel(new BorderLayout());
this.pnlVehicles.setPreferredSize(new Dimension(400, 500));
this.pnlVehicles.add(this.pnlLorry, BorderLayout.NORTH);
this.pnlVehicles.add(this.pnlCars, BorderLayout.AFTER_LAST_LINE);
this.add(this.pnlVehicles, BorderLayout.EAST);
}
public int[] findEmptySpace(int start, int end) {
for (int row = 0; row < vehicles.length; row++) {
for (int column = start; column < end; column++) {
//Check if space is empty
if (this.getVehicle(row, column) == null) {
return new int[]{
row,
column
};
}
}
}
return null;
}
public void setVehicle(int x, int y, Vehicle vehicle) {
this.vehicles[x][y] = vehicle;
//TODO: Render vehicle in GUI. Check for null and remove
ImageIcon image;
if (vehicle != null) {
image = vehicle.getImage();
} else {
image = null;
}
((ImagePanel) this.pnlCars.getComponent(x + (y - 1) * (this.vehicles.length - 1))).setImage(image);
//TODO: Update totals
}
public Vehicle getVehicle(int x, int y) {
return this.vehicles[x][y];
}
private void addCarMethod() {
btnAddCar.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
//TODO: Create car input form.
//REQUIREMENTS: registration, length, disabled
final int[] value = findEmptySpace(1, vehicles.length);
if (value != null) {
//SHOW FORM
final JFrame frame = new JFrame("Add Car");
frame.setSize(350, 150);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Labels = new GridLayout(4, 2);
FormLayout = new GridLayout(2, 1);
pnlForm = new JPanel();
pnlFormButton = new JPanel();
frame.setLayout(FormLayout);
frame.add(pnlForm);
frame.add(pnlFormButton);
pnlForm.setLayout(null);
pnlForm.setLayout(Labels);
JLabel reg = new JLabel("Registration Number:");
pnlForm.add(reg);
final JTextField regTxt = new JTextField(20);
pnlForm.add(regTxt);
JLabel length = new JLabel("Length: ");
pnlForm.add(length);
final JTextField lengthTxt = new JTextField(20);
pnlForm.add(lengthTxt);
JLabel disBadge = new JLabel("Disabled Badge: ");
pnlForm.add(disBadge);
final JTextField disBadgeTxt = new JTextField(20);
pnlForm.add(disBadgeTxt);
JButton ok = new JButton("Ok");
pnlFormButton.setLayout(FormLayout);
pnlFormButton.add(ok);
frame.setVisible(true);
ok.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
String regNumber = regTxt.getText();
System.out.println("ok");
double length = Double.parseDouble(lengthTxt.getText());
boolean BadgeBoolean;
if (disBadgeTxt.equals("yes")) {
BadgeBoolean = true;
} else {
BadgeBoolean = false;
}
Car vehicle = new Car(regNumber, length, BadgeBoolean, 1);
System.out.println(String.valueOf(value[0]) + ":" + String.valueOf(value[1]));
setVehicle(value[0], value[1], vehicle);
frame.dispose();
}
});
} else {
warningMethod();
}
}
});
}
答案 0 :(得分：1)
你的问题是这一行：
this.pnlCars.getComponent(x + (y - 1) * (this.vehicles.length - 1))
返回一个JPanel实例，而不是一个ImagePanel实例，其原因未在您发布的代码中显示。以这种方式使用getComponent(...)是一件危险且脆弱的事情，如果我们能够更多地了解您的计划，可以使用更好的方法。为了获得更好的帮助，请考虑创建并发布Minimal, Complete, and Verifiable Example Program，其中您将代码压缩到仍然编译和运行的最小位，没有外部依赖（例如需要链接到数据库或图像），没有额外的代码这与您的问题无关，但仍然可以证明您的问题。
顺便说一下，这行违规代码，
((ImagePanel) this.pnlCars.getComponent(x + (y - 1) * (this.vehicles.length - 1)))
.setImage(image);}
太长了，并且试图做得太多，使得调试比实际需要更困难。代码空间很便宜，因此将其分成几行，以便于阅读和调试。
修改
您正在将JPanels（此处称为pnlVehicle）添加到您的pnlCars JPanel对象中：
this.pnlCars.add(pnlVehicle);
因此，如果您尝试从pnlVehicle JPanel中提取组件，那么它实际上是一个JPanel而不是ImagePanel（无论是什么）。你的错误不应该让你感到惊讶。