问题
In my java application, my objective is to display or output an image using MVC architecture. My java application is comprised of an imagecontroller(main), imageview, and image model. I am currently able to select an image, the compiler acknowledges where the image has been selected from in the c: drive however it does not output or display the image. Here is a copy of my code below:
package imagecontroller;
import javax.swing.SwingUtilities;
import java.io.File;
public class ImageController {
private final ImageModel model;
private final ImageView view;
public ImageController () {
this.view = new ImageView(this);
this.model = new ImageModel(this.view);
public static void launch () {
new ImageController();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(ImageController::launch);
}
}
package imagecontroller;
import java.awt.Dimension;
import java.io.File;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.filechooser.FileNameExtensionFilter;
public class ImageView extends JFrame{
private final ImageController controller;
public ImageView(ImageController controller) {
this.controller = controller;
JFileChooser Chooser = new JFileChooser();
FileNameExtensionFilter filter = new FileNameExtensionFilter("JPG & PNG Images", "jpg", "png");
Chooser.addChoosableFileFilter(filter);
Chooser.setCurrentDirectory(new File(System.getProperty("user.home")));
Chooser.setFileSelectionMode(JFileChooser.FILES_ONLY);
int result
Chooser.showOpenDialog(null);
if (result == JFileChooser.APPROVE_OPTION) {
Chooser.setAcceptAllFileFilterUsed(true);
File selectedFile = Chooser.getSelectedFile();
System.out.println("Selected file: " + selectedFile.getAbsolutePath());
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.setTitle("ImageAnnotator");
frame.setVisible(true);
frame.setSize(new Dimension (500,500));
}
}
}
package imagecontroller;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JComponent;
import javax.swing.JOptionPane;
public class ImageModel extends JComponent {
private final ImageView view;
private BufferedImage image;
public ImageModel(ImageView view) {
this.view = view;
}
public void CustomComponent (File png) {
BufferedImage image = null;
setPreferredSize(new Dimension(400, 400));
try {
this.image = ImageIO.read(new File("640px-Pleiades_large.png"));
} catch (IOException x) {
JOptionPane.showMessageDialog(null, "Not an ImageFile, Please Select an Image");
}
}
@Override
public void paintComponent(Graphics g){
super.paintComponent(g);
g = g.create();
g.setColor(Color.WHITE);
g.fillRect(0, 0, getWidth(), getHeight());
int margin = 20;
int w = (getWidth() - (2 * margin + 2)) / 2;
int h = this.image.getHeight() * w / this.image.getWidth();
g.drawImage(image, h, h, WIDTH, HEIGHT, view);
}
}
回答1:
The reason that the MVC pattern is called the MVC pattern is that the name suggests the order. In other words, create the model, then the view, then the controllers.
Here's an image display GUI I put together.
So, let's start with the model. For an image viewer GUI, the model is pretty simple.
public class ImageDisplayModel {
private BufferedImage image;
private File file;
public BufferedImage getImage() {
return image;
}
public void setImage(BufferedImage image) {
this.image = image;
}
public File getFile() {
return file;
}
public void setFile(File file) {
this.file = file;
}
}
The ImageDisplayModel class is a plain Java class that holds a BufferedImage and a File path. By saving the File path, the next time the user selects an image, the directory will be set to be the same as the last image.
The ImageDisplayModel class is an ordinary getter / setter class.
The next step is to create the view.
public class ImageDisplay implements Runnable {
public static void main(String[] args) {
SwingUtilities.invokeLater(new ImageDisplay());
}
private ImageDisplayModel model;
private ImagePanel imagePanel;
private JFrame frame;
public ImageDisplay() {
this.model = new ImageDisplayModel();
}
@Override
public void run() {
frame = new JFrame("Image Display");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setJMenuBar(createMenuBar());
imagePanel = new ImagePanel(model);
frame.add(imagePanel, BorderLayout.CENTER);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
private JMenuBar createMenuBar() {
JMenuBar menubar = new JMenuBar();
JMenu filemenu = new JMenu("File");
JMenuItem openitem = new JMenuItem("Open...");
openitem.addActionListener(new OpenFileListener(this, model));
filemenu.add(openitem);
menubar.add(filemenu);
return menubar;
}
public void updateImagePanel(int width, int height) {
imagePanel.setPreferredSize(width, height);
imagePanel.repaint();
frame.pack();
}
public JFrame getFrame() {
return frame;
}
}
We start the application with a call to the SwingUtilities invokeLater method. This method ensures that the Swing components are created and executed on the Event Dispatch Thread.
The view constructor instantiates the application model.
The JFrame code is in the run method.
The JMenuBar method allows us to select multiple images, one after the other.
The getFrame method allows the eventual controller class to access the JFrame instance. The updateImagePanel method allows the eventual controller class to update the image panel.
Next, we create the DrawingPanel class.
public class ImagePanel extends JPanel {
private static final long serialVersionUID = 1L;
private ImageDisplayModel model;
public ImagePanel(ImageDisplayModel model) {
this.model = model;
this.setPreferredSize(649, 480);
}
public void setPreferredSize(int width, int height) {
this.setPreferredSize(new Dimension(width, height));
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
BufferedImage image = model.getImage();
if (image != null) {
g.drawImage(image, 0, 0, this);
}
}
}
Simple and straightforward. We draw the BufferedImage if one exists. We also adjust the size of the JPanel so that the image fits.
The only information that the DrawingPanel class needs is the model class. The drawing panel will draw the image. Period.
Finally, we create the controller class.
public class OpenFileListener implements ActionListener {
private ImageDisplay frame;
private ImageDisplayModel model;
public OpenFileListener(ImageDisplay frame, ImageDisplayModel model) {
this.frame = frame;
this.model = model;
}
@Override
public void actionPerformed(ActionEvent event) {
JFileChooser chooser = new JFileChooser();
FileNameExtensionFilter filter = new FileNameExtensionFilter(
"JPG & PNG Images", "jpg", "png");
chooser.addChoosableFileFilter(filter);
chooser.setFileSelectionMode(JFileChooser.FILES_ONLY);
File file = model.getFile();
if (file != null) {
chooser.setCurrentDirectory(file);
}
int result = chooser.showOpenDialog(frame.getFrame());
if (result == JFileChooser.APPROVE_OPTION) {
File selectedFile = chooser.getSelectedFile();
model.setFile(selectedFile);
BufferedImage image;
try {
image = ImageIO.read(selectedFile);
model.setImage(image);
frame.updateImagePanel(image.getWidth(),
image.getHeight());
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
The controller class updates the model information and instructs the view to repaint itself. The controller isn't concerned with the view internals. All the controller needs to know is that the view can update.
Finally, here's the complete runnable code. I made the classes inner classes so I could post this code as one block.
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.filechooser.FileNameExtensionFilter;
public class ImageDisplay implements Runnable {
public static void main(String[] args) {
SwingUtilities.invokeLater(new ImageDisplay());
}
private ImageDisplayModel model;
private ImagePanel imagePanel;
private JFrame frame;
public ImageDisplay() {
this.model = new ImageDisplayModel();
}
@Override
public void run() {
frame = new JFrame("Image Display");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setJMenuBar(createMenuBar());
imagePanel = new ImagePanel(model);
frame.add(imagePanel, BorderLayout.CENTER);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
private JMenuBar createMenuBar() {
JMenuBar menubar = new JMenuBar();
JMenu filemenu = new JMenu("File");
JMenuItem openitem = new JMenuItem("Open...");
openitem.addActionListener(new OpenFileListener(this, model));
filemenu.add(openitem);
menubar.add(filemenu);
return menubar;
}
public void updateImagePanel(int width, int height) {
imagePanel.setPreferredSize(width, height);
imagePanel.repaint();
frame.pack();
}
public JFrame getFrame() {
return frame;
}
public class ImagePanel extends JPanel {
private static final long serialVersionUID = 1L;
private ImageDisplayModel model;
public ImagePanel(ImageDisplayModel model) {
this.model = model;
this.setPreferredSize(649, 480);
}
public void setPreferredSize(int width, int height) {
this.setPreferredSize(new Dimension(width, height));
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
BufferedImage image = model.getImage();
if (image != null) {
g.drawImage(image, 0, 0, this);
}
}
}
public class OpenFileListener implements ActionListener {
private ImageDisplay frame;
private ImageDisplayModel model;
public OpenFileListener(ImageDisplay frame, ImageDisplayModel model) {
this.frame = frame;
this.model = model;
}
@Override
public void actionPerformed(ActionEvent event) {
JFileChooser chooser = new JFileChooser();
FileNameExtensionFilter filter = new FileNameExtensionFilter(
"JPG & PNG Images", "jpg", "png");
chooser.addChoosableFileFilter(filter);
chooser.setFileSelectionMode(JFileChooser.FILES_ONLY);
File file = model.getFile();
if (file != null) {
chooser.setCurrentDirectory(file);
}
int result = chooser.showOpenDialog(frame.getFrame());
if (result == JFileChooser.APPROVE_OPTION) {
File selectedFile = chooser.getSelectedFile();
model.setFile(selectedFile);
BufferedImage image;
try {
image = ImageIO.read(selectedFile);
model.setImage(image);
frame.updateImagePanel(image.getWidth(),
image.getHeight());
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
public class ImageDisplayModel {
private BufferedImage image;
private File file;
public BufferedImage getImage() {
return image;
}
public void setImage(BufferedImage image) {
this.image = image;
}
public File getFile() {
return file;
}
public void setFile(File file) {
this.file = file;
}
}
}
回答2:
I really found this interesting and thought to explore it a little more. Taking pointers from The MVC pattern and Swing (which I suggest you read especially the accepted answer) lets try have a go.
Explanation:
Brief Summary of the code to follow (based off of the above link)
The LoginView. The view is simply your UI components, with getter methods for any components needed by the LoginController as well as implementing a PropertyChangeListener which is used by the view to receive PropertyChangeEvents which could be fired by our LoginController or LoginModel.
The LoginController The controller has access to both the view and the model. The controller sets up the necessary events on the views components and reacts to them by validating input from the view and then asks the model to do its job and potentially that will change its state. The controller takes your views actions and interprets them. If you click on a button, it's the controller's job to figure out what that means and how the model should be manipulated based on that action.
The controller may also ask the view to change it does this by subscribing the view (which implements PropertyChangeListener) to its SwingPropertyChangeSupport. When the controller receives an action from the view, in this case the Login button pressed it validates inputs from the view and fires the necessary validation errors (if any). It then calls the model to do the actual validation.
The LoginModel The controller calls methods on the model which intern notifies the view when its state has changed. When something changes in the model, based either on some action you took (like clicking a button) the model notifies the view that its state has changed through the same mechanism as the controller.
The view can also ask the model for state. The view gets the state it displays directly from the model. For instance, if we pass in a model instance to our view which already has authenticated set to true, you will immediately receive the message to say you are logged in (this has not been demonstrated here, but would entail passing the model into the views constructor and after initializing the initView() doing something like onAuthenticatedPropertyChange(model.isAuthenticated())).
Some extra information is both controller and model implement the observer pattern (as in the view observes changes to the controller and models in order to react to them) The controller also does all model execution on a background thread via a SwingWorker, and all property change listeners are fired back on the EDT
Here is the code which demonstrates the above:
TestApp.java:
import javax.swing.SwingUtilities;
public class TestApp {
public TestApp() {
createAndShowGUI();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(TestApp::new);
}
private void createAndShowGUI() {
LoginModel model = new LoginModel();
LoginView view = new LoginView();
LoginController controller = new LoginController(view, model);
}
}
LoginView.java:
import java.awt.Color;
import java.awt.Component;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.border.EmptyBorder;
public class LoginView implements PropertyChangeListener {
private JFrame frame;
private JPanel loginPanel;
private JTextField usernameTextField;
private JTextField passwordTextField;
private JLabel errorLabel;
private JButton loginButton;
public LoginView() {
initView();
}
private void initView() {
frame = new JFrame("TestApp");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
loginPanel = createLoginPanel();
frame.add(loginPanel);
frame.pack();
frame.setVisible(true);
}
private JPanel createLoginPanel() {
JPanel panel = new JPanel();
panel.setBorder(new EmptyBorder(20, 20, 20, 20));
panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
JLabel usernameLabel = new JLabel("Username:");
usernameLabel.setAlignmentX(Component.CENTER_ALIGNMENT);
usernameTextField = new JTextField();
usernameTextField.setAlignmentX(Component.CENTER_ALIGNMENT);
usernameTextField.setColumns(20);
JLabel passwordLabel = new JLabel("Password:");
passwordLabel.setAlignmentX(Component.CENTER_ALIGNMENT);
passwordTextField = new JTextField();
passwordTextField.setAlignmentX(Component.CENTER_ALIGNMENT);
passwordTextField.setColumns(20);
loginButton = new JButton("Login");
loginButton.setAlignmentX(Component.CENTER_ALIGNMENT);
errorLabel = new JLabel();
errorLabel.setForeground(Color.RED);
errorLabel.setAlignmentX(Component.CENTER_ALIGNMENT);
errorLabel.setVisible(false);
panel.add(usernameLabel);
panel.add(usernameTextField);
panel.add(passwordLabel);
panel.add(passwordTextField);
panel.add(errorLabel);
panel.add(loginButton);
return panel;
}
public JButton getLoginButton() {
return loginButton;
}
public JTextField getUsernameTextField() {
return usernameTextField;
}
public JTextField getPasswordTextField() {
return passwordTextField;
}
public JFrame getFrame() {
return frame;
}
@Override
public void propertyChange(PropertyChangeEvent evt) {
String propertyName = evt.getPropertyName();
Object newValue = evt.getNewValue();
switch (propertyName) {
case "authenticated":
// authentication has finished lets do something
onAuthenticatedPropertyChange((Boolean) newValue);
break;
case "authenticating":
// lets disable the UI as we authenticate
errorLabel.setVisible(false);
disableLoginPanelComponents(true);
break;
case "usernameInvalid":
showError((String) newValue);
break;
case "passwordInvalid":
showError((String) newValue);
break;
}
}
private void onAuthenticatedPropertyChange(Boolean authenticated) {
if (authenticated == true) {
errorLabel.setVisible(false);
JOptionPane.showMessageDialog(frame, "You are in!");
} else {
showError("Invalid username or password!");
}
// re-enable components after authentication regadless of fail or pass
disableLoginPanelComponents(false);
}
private void showError(String error) {
errorLabel.setText(error);
errorLabel.setVisible(true);
}
private void disableLoginPanelComponents(boolean disable) {
for (int i = 0; i < loginPanel.getComponentCount(); i++) {
Component component = (Component) loginPanel.getComponent(i);
if (component instanceof JTextField || component instanceof JButton) {
((JComponent) loginPanel.getComponent(i)).setEnabled(!disable);
}
}
}
}
LoginController:
import java.awt.event.ActionEvent;
import javax.swing.SwingWorker;
import javax.swing.event.SwingPropertyChangeSupport;
public class LoginController {
private final SwingPropertyChangeSupport propertyChangeSupport;
private final LoginView view;
private final LoginModel model;
public LoginController(LoginView view, LoginModel model) {
this.view = view;
this.model = model;
propertyChangeSupport = new SwingPropertyChangeSupport(this, true);
initController();
}
private void initController() {
// make the view a listener of both the model and controller as both can send events which the view must react too
model.addPropertyChangeListener(view);
propertyChangeSupport.addPropertyChangeListener(view);
view.getLoginButton().addActionListener((ActionEvent e) -> {
// lets do some basic validation of username and password fields
String username = view.getUsernameTextField().getText();
String password = view.getPasswordTextField().getText();
// validate user input before sending it to the model (this is the contorllers job - besdoes business rules i..e username doesnt exist etc)
if (username.isEmpty()) {
propertyChangeSupport.firePropertyChange("usernameInvalid", null, "Username cannot be empty!");
return;
}
if (password.isEmpty()) {
propertyChangeSupport.firePropertyChange("passwordInvalid", null, "Password cannot be empty!");
return;
}
// call the model to login on a background thread as the model may query the db or hit an API etc
new SwingWorker<Void, Void>() {
@Override
protected Void doInBackground() throws Exception {
model.login(username, password);
return null;
}
}.execute();
});
}
}
LoginModel.java:
import java.beans.PropertyChangeListener;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.event.SwingPropertyChangeSupport;
public class LoginModel {
private final SwingPropertyChangeSupport propertyChangeSupport;
private boolean authenticated;
public LoginModel() {
propertyChangeSupport = new SwingPropertyChangeSupport(this, true); // we pass in true to noifty observers on the Event Dispatch Thread
}
public void login(String username, String password) {
propertyChangeSupport.firePropertyChange("authenticating", null, true);
// lets simulate query a database or something for 3 seconds
try {
Thread.sleep(3000);
} catch (InterruptedException ex) {
Logger.getLogger(LoginModel.class.getName()).log(Level.SEVERE, null, ex);
}
authenticated = username.equals("admin") && password.equals("password");
propertyChangeSupport.firePropertyChange("authenticated", null, authenticated);
}
public void addPropertyChangeListener(PropertyChangeListener prop) {
propertyChangeSupport.addPropertyChangeListener(prop);
}
public boolean isAuthenticated() {
return authenticated;
}
}
The above is generic and doesn't directly answer YOUR question but gives you an example of an MVC pattern in Swing.
Update:
Here is an example specific to your issue
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.image.BufferedImage;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.border.EmptyBorder;
import javax.swing.border.LineBorder;
import javax.swing.event.SwingPropertyChangeSupport;
import javax.swing.filechooser.FileNameExtensionFilter;
public class TestApp {
public TestApp() {
createAndShowGUI();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(TestApp::new);
}
private void createAndShowGUI() {
DisplayImageModel model = new DisplayImageModel();
DisplayImageView view = new DisplayImageView();
DisplayImageController controller = new DisplayImageController(view, model);
}
class DisplayImageView implements PropertyChangeListener {
private JFrame frame;
private ImagePanel imagePanel;
private JLabel imageLabel;
private JButton pickImageButton;
public DisplayImageView() {
initView();
}
private void initView() {
frame = new JFrame("TestApp");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = createImagePanel();
frame.add(panel);
frame.pack();
frame.setVisible(true);
}
private JPanel createImagePanel() {
JPanel panel = new JPanel();
panel.setBorder(new EmptyBorder(20, 20, 20, 20));
panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
pickImageButton = new JButton("Pick an image");
pickImageButton.setAlignmentX(Component.CENTER_ALIGNMENT);
imagePanel = new ImagePanel();
imagePanel.getPanel().setAlignmentX(Component.CENTER_ALIGNMENT);
panel.add(imagePanel.getPanel());
panel.add(pickImageButton);
return panel;
}
public JButton getPickAnImageButton() {
return pickImageButton;
}
public JLabel getImageLabel() {
return imageLabel;
}
public JFrame getFrame() {
return frame;
}
@Override
public void propertyChange(PropertyChangeEvent evt) {
String propertyName = evt.getPropertyName();
Object newValue = evt.getNewValue();
switch (propertyName) {
case "image":
onImagePropertyChange((BufferedImage) newValue);
break;
}
}
private void onImagePropertyChange(BufferedImage image) {
imagePanel.setImage(image);
frame.pack();
}
}
class DisplayImageModel {
private final SwingPropertyChangeSupport propertyChangeSupport;
private BufferedImage image;
public DisplayImageModel() {
propertyChangeSupport = new SwingPropertyChangeSupport(this, true); // we pass in true to noifty observers on the Event Dispatch Thread
}
public void setImage(BufferedImage image) {
this.image = image;
propertyChangeSupport.firePropertyChange("image", null, image);
}
public void addPropertyChangeListener(PropertyChangeListener prop) {
propertyChangeSupport.addPropertyChangeListener(prop);
}
public BufferedImage getImage() {
return image;
}
}
class DisplayImageController {
private final SwingPropertyChangeSupport propertyChangeSupport;
private final DisplayImageView view;
private final DisplayImageModel model;
public DisplayImageController(DisplayImageView view, DisplayImageModel model) {
this.view = view;
this.model = model;
propertyChangeSupport = new SwingPropertyChangeSupport(this, true);
initController();
}
private void initController() {
// make the view a listener of both the model and controller as both can send events which the view must react too
model.addPropertyChangeListener(view);
propertyChangeSupport.addPropertyChangeListener(view);
view.getPickAnImageButton().addActionListener((ActionEvent e) -> {
JFileChooser chooser = new JFileChooser();
FileNameExtensionFilter filter = new FileNameExtensionFilter(
"JPG & PNG Images", "jpg", "png");
chooser.addChoosableFileFilter(filter);
chooser.setFileSelectionMode(JFileChooser.FILES_ONLY);
int result = chooser.showOpenDialog(view.getFrame());
if (result == JFileChooser.APPROVE_OPTION) {
File selectedFile = chooser.getSelectedFile();
BufferedImage image;
try {
image = ImageIO.read(selectedFile);
model.setImage(image);
} catch (IOException ex) {
ex.printStackTrace();
}
}
});
}
}
class ImagePanel {
private final JPanel panel;
private BufferedImage image;
public ImagePanel() {
this.panel = new JPanel() {
@Override
public Dimension getPreferredSize() {
if (image != null) {
return new Dimension(image.getWidth(), image.getHeight());
} else {
return new Dimension(200, 200);
}
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (image != null) {
g.drawImage(image, 0, 0, this);
}
}
};
panel.setBorder(new LineBorder(Color.GRAY, 1));
}
public void setImage(BufferedImage image) {
this.image = image;
panel.revalidate();
panel.repaint();
}
public JPanel getPanel() {
return panel;
}
}
}
来源：https://stackoverflow.com/questions/65176251/how-do-i-display-an-image-in-java-swing-mvc-architecture