Thread: repaint from another class!

Hi, as the topic follows im trying to repaint a window from another class. the class Window handles an interface that displays pictures of movies. Via a JMenuBar you can add a new movie and its picture but in order for it to show in the Window i need to repaint certain aspects in the Window class GUI;

The window class constructor:

	public Window() {
		addComponents();
		configurFrame();
		addMenu();
	}

The functions i want to repaint:

	public void repaintWindow() {
		this.getContentPane().validate();
		this.getContentPane().repaint();
	}

From my other class where i add a movie to an ArrayList i have made a "private Window myWindow;" there i call the function repaintWindow via mywindow.repaintWindow(); But this gives me an NullPointerException related to the repaintWindow function.

Any suggestions?

Errors you say:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at project.MediaHandler.addMovie(MediaHandler.java:19)
	at project.AddMovieWindow.addMedia(AddMovieWindow.java:73)
	at project.AddMovieWindow$ButtonListener.actionPerformed(AddMovieWindow.java:23)
	at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
	at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
	at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
	at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
	at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
	at java.awt.Component.processMouseEvent(Unknown Source)
	at javax.swing.JComponent.processMouseEvent(Unknown Source)
	at java.awt.Component.processEvent(Unknown Source)
	at java.awt.Container.processEvent(Unknown Source)
	at java.awt.Component.dispatchEventImpl(Unknown Source)
	at java.awt.Container.dispatchEventImpl(Unknown Source)
	at java.awt.Component.dispatchEvent(Unknown Source)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
	at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
	at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
	at java.awt.Container.dispatchEventImpl(Unknown Source)
	at java.awt.Window.dispatchEventImpl(Unknown Source)
	at java.awt.Component.dispatchEvent(Unknown Source)
	at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
	at java.awt.EventQueue.access$200(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue$4.run(Unknown Source)
	at java.awt.EventQueue$4.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue.dispatchEvent(Unknown Source)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.run(Unknown Source)

It goes back to the function i call:

	public void repaintWindow() {
		this.getContentPane().validate();
		this.getContentPane().repaint();
	}

I'm not sure if i can call the repaint. I haven't declared a paintComponent eg, is there any other way of refreshing the content?

--- Update ---

I could also add that these are the functions i'm trying to repaint:

	private void addComponents() {
		JPanel shelfs = buildShelfs();
		this.add(shelfs);
	}
 
	private JPanel buildShelfs() {
		JPanel mediaPanel = new JPanel();
		int nrOfMedias = myMediaHandler.mediaList.size();
		mediaPanel.setOpaque(false);
		mediaPanel.setLayout(new GridLayout(3,6,22,30));
		mediaPanel.setBounds(90, 25, 1020, 745);
 
				java.net.URL where;
				for(int i = 0; i < nrOfMedias; i++) {
					String temp = myMediaHandler.mediaList.get(i).getImagePath();
					try {
						where = new URL(temp);
						ImageIcon image = new ImageIcon(where);
						JLabel imageLabel = new JLabel(image);
						mediaPanel.add(imageLabel);
					} catch (MalformedURLException e) {
						// TODO Auto-generated catch block
						System.out.println("Error loading user media picture");
						e.printStackTrace();
					}
				}
 
			java.net.URL where1;
			try {
				for(int i = nrOfMedias; i < 18; i++) {
					where1 = new URL("https://dl.dropboxusercontent.com/u/16670644/Projekt/TempPic.png");
					ImageIcon image1 = new ImageIcon(where1);			
					JLabel imageLabel1 = new JLabel(image1);
					mediaPanel.add(imageLabel1);
				}
 
			} catch (MalformedURLException e) {
				// TODO Auto-generated catch block
				System.out.println("Error loading TempPic that shows allowed media spots");
				e.printStackTrace();
			}
 
			return mediaPanel;
	}

A reference to the object being repainted in the class doing the repainting is all that is needed. If the object being repainted is a JPanel, provide a reference to that JPanel by passing it through the repainting class' constructor or using an appropriate getter/setter method.

If you provide a simple example of two classes where one class is calling repaint() on an object created in another class, we can show you how to do what I've described. Pretty simple but can be hard to grasp at first.

Okay, this is a tricky one. I tried to rebuild the shelf's by simply calling:

	private void addComponents() {
		JPanel shelfs = buildShelfs();
		this.add(shelfs);
	}

And this as far as i can tell builds a new shelf with all its updates. However it lays beneath the "old" shelf so i really don't know how to work around this.

I also changer the MediaHandlers constructor so i can access the Window class but i'm not sure if i'm doing it right.

	private Window myWindow;
 
	public MediaHandler(Window window) {
		this.mediaList = new ArrayList<Media>();
		myWindow = window;
	}

Thanks for the comments guys it helped me figure some things out but i'm still stuck on the repainting stuff.

I can't follow what you're doing or understand what you're trying to do. Please post code that we can run to demonstrate the problem.