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Thread: repaint from another class!

  1. #1
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    Default 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?


  2. #2
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    Default Re: repaint from another class!

    gives me an NullPointerException
    Please copy the full text of the error message and paste it here. It has important info about the error.
    To call a method in another class, the code needs a reference to the instance of the other class.

    BTW Window is the name of a Java SE class. Using Java SE class names will cause confusion for people reading the code.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: repaint from another class!

    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)

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    Default Re: repaint from another class!

    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at project.MediaHandler.addMovie(MediaHandler.java:19 )
    At line 19 the code improperly used a null value, possibly contained in a variable. Look at line 19 and find where the null value is and backtrack in the code to see where it came from.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: repaint from another class!

    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;
    	}

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    Default Re: repaint from another class!

    these are the functions i'm trying to repaint:
    I'm not sure what you mean by that. methods are not repainted.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: repaint from another class!

    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.

  8. The Following User Says Thank You to GregBrannon For This Useful Post:

    sebbe605 (April 2nd, 2014)

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    Default Re: repaint from another class!

    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.

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    Default Re: repaint from another class!

    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.

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