I have several JPanels that contain buttons, labels, etc. that I want to switch between from a main JFrame. Currently I am trying to use the this.add(JPanelname); method and this.remove(JPanelname); with the validate(); and repaint(); methods
The problem is it will add the panel to the JFrame but it will not remove it. I am not sure how exactly to go about this.
Maybe you should be using a Card Layout.
Or maybe you should be using modal JDialogs. So whenever you click on the "widjet" a new window is displayed. Then when you close the dialog you are back on your main frame.
If you are constantly switching between JPanels, then a JTabbedPane may be the right thing to use. It should not be necessary to call "validate" or "repaint" when you add or remove a JPanel. Do you have a layout manager installed? Do you make sure to call add/remove only within the UI event thread? Also, typically one does not call "validate()" but rather "invalidate()" to invalidate the container for updates.
Related
I am now writing code simple GUI that's for start the game window. I only need Do you want to start game message and start button on the window. But I have a confusing concepts for the JFrame and JPanel. Actually, I thought I need to add JPanel to JFrame to add the other components such as JLabel, JButton,...etc. But I realized I don't actually need JPanel. I can just add the components simply use add(button), add(label) to JFrame. So why I need JPanel. And I think JFrame doesn't need JPanel but JPanel need JFrame. Am I understand correctly?
No, not always. A simple graphical user interface may be implemented by just adding components "directly" to a JFrame. But in order to get more flexibility, you would always use JPanels. For example, to employ different layouts in different parts of the GUI, to group certain components together, etc.
A JFrame is backed by a JRootPane, a part of which is a contentPane.
(image from Oracle Javadoc)
When you add components to a JFrame, you are really adding them to the content pane, e.g.: frame.getContentPane().add(Component).
A JFrame is a common starting scene of a Swing GUI application, while a JPanel is intended to be put in another scene (container). Since both content pane and a JPanel inherit from the same class (Container) you may use them in a similar manner, as far as adding components to them goes.
Do I need JPanel always?
No. Well, unless you need a Swing GUI. Then yes.
Another answer replied words to the effect. "No, you can add components direct to a frame" What they missed was that components added to a JFrame are added to the content pane (automatically). The content pane is a JPanel.
Having said that:
I (and many others) would recommend designing an app based around a main content panel, then adding that panel to a top-level container as needed. The top level container might be a JFrame, JWindow, JDialog, JOptionPane ..
What prompted the question? A JPanel is a very 'light weight' container (in more ways than one). A GUI can contain 1000s and not be burdened by doing so. Of course, that's a rare requirement, but just saying .. use panels as needed and don't worry about it.
I have Main class, StartFrame extends JFrame, and UserPanel extends JPanel which I add to StartFrame. I have button in the UserPanel, how can I close StartFrame when I press the button(I am familiar with event handling it's not a problem the issue is how to sent info to the StartFrame) . Or it is better to just change the panel of the frame(size if need) and reuse it?
If you want to close a window that is enclosing a component, you need a reference to that Window, and SwingUtilities has a method that can help you get this: getWindowAncestor(Component c). Then you could call dispose() on the window returned.
i.e.,
Window win = SwingUtilities.getWindowAncestor(myJPanel);
win.dispose();
Note that this is fine if you're using this to end your GUI, but if your goal is to swap views, then a better suggestion is not to swap Windows, but rather to leave the main JFrame visible but to instead swap components it shows with a CardLayout.
The button is already on the frame (on the upper right, here). Just call JFrame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE) when constructing it and it will work as the user expects.
Other tip
Don't extend frame or panel, but instead just create and use them.
Think about the classic installation process, where you have a "next" button and when you click it the content of the window changes. To represent this situation I thought of two possible solutions:
-when "next" is clicked destroy the current JFrame and create a new JFrame, maybe passing to his constructor useful information (e.g. actual window size, content inserted by the user in the current frame, ...)
-when "next" is clicked remove all the components from the current JFrame and add new components as needed
The first solution looks way better about OOprogramming, because I can keep separate classes for different frames and I can avoid huge methods that empty the frame and repopulate it. However the first solution sounds a bit "dirty" and I should pass lots of parameters to the new frame. To represent this situation I would choose the second solution.
Now think about a menu with an "option" component: in this situation I would create a new JFrame when "option" is clicked, so that I can populate it with option items. Is this a correct solution? Is there a way I can always know which one is the best solution? Are there any solutions I didn't think about?
Destroying the main JFrame would be silly -- not to mention jarring for the user. Just use a single JFrame and change its contents.
To implement an installer wizard, use a single JFrame containing one large JPanel on top and a smaller one containing the "Next", "Back", "Cancel" buttons along the bottom. When the Next or Back buttons are pressed, you replace the large JPanel. You can have many different JPanel subclasses, one for each "page" of the wizard.
There's a LayoutManager called CardLayout which is ideal for implementing this scenario -- it manages a "stack" of components, and only shows one of those components at a time. Use a BorderLayout in the JFrame. Into the center position put a JPanel with a CardLayout. Then add the individual pages of the wizard to that JPanel, so the CardLayout can manage them.
The CardLayout is well suited for this. You just swapout the JPanel contents when the "Next" button is pressed.
How do you refresh a JPanel on the panel change from container CardLayout?
Use the show() method. From the Java API:
Flips to the component that was added to this layout with the specified name, using addLayoutComponent. If no such component exists, then nothing happens.
CardLayout#first(), next(), and previous() do something similar.
Sometimes, when I've made a panel swap like this (though not that I can remember on CardLayout, but it's been a while since I used it), I've also needed to pack the frame again. If that doesn't work, you can call revalidate(), which lets Swing know that the component needs to be redrawn.
You may also want to consider using a tabbed pane, as it does a lot of this for you; I started out a project trying to use CardLayout and decided to use a the tabbed pane instead. Depends on what you want to do, of course.
Is there an actionlistener or something that I can have it reload/refresh my data on that screen?
Assuming you have a model that supplies data to your view (panel), two approaches are common:
Arrange for your model to extend Observable and your view to register as an Observer.
Arrange for your model to manage an EventListenerList, in effect creating you own analog of ActionEvent.
In either approach, use the listener of the control that switches views tell the model to update its registered observers/listeners. The example in How to Use CardLayout uses a JComboBox and itemStateChanged(). There's additional discussion here.
Is there an actionlistener or
something that I can have it
reload/refresh my data on that screen?
You can use an AncestorListener. It fires when a component is added to a Container. So when you swap cards the event is fired. You would need to add the listener to each panel you add to the CardLayout:
Another problem with the CardLayout is that the panel doesn't gain focus when it is swapped. I use this approach to set focus on the panel. Check out Card Layout Focus.
panel.addAncestorListener(...);
The show() method does the trick of switching panels, but it doesn't "refresh" the data. Is there an actionlistener or something that I can have it reload/refresh my data on that screen?
I'm creating a simple java game Applet that has multiple Panels, The main game Panel has 4 JButtons that lead to the rest of the Panels when they are clicked.
when the program runs, the four Panels are initialized 1st inside the init(), and inside each Panel initialization, I made all the Jcomponents invisible but only the main applet.
lets say there is a JButton in the main Applet Called start, when it's pressed, i need to set all the main JButtons to invisible, and set the sub Panel to visible but it's not working for me, I used everything I could think of, like repaint() or UpdateUI() but still not working.
any suggestions would be much appreciated.
Cheers
First, ensure all creation is performed not in init(), but in the EDT, see the tutorial. If you have an ampty start() method I'd recommend you use invokeLater in the init() (instead of the tutorial recommendation of invokeAndWait).
To hide buttons simply call setVisible on the JButton. There should be no need to ask for a repaint afterwards.
Further analysis is difficult without seeing the code.