I have questions regarding JFrames and Jcomponents.
Firstly, Can we add multiple Jcomponents
to a JFrame?
Secondly, if we do add multiple jcomponents to a JFrame then how do we repaint all of them when we want to do so ?
You're always going to have a tree structure in your UI, because JFrame is the root of it. So yes, you can have multiple components but they will be siblings in a parent. Use that parent (eith the JFrame or its content pane) as the target for your repainting calls, and it should propagate through the entire UI.
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 a problem where I have several similar JPanels, that are contained vertically in a main JPanel. My issue comes where I will have buttons that will only interact with the child JPanel that is currently selected (clicked on).
I have a controller that takes the main JPanel, how can I have a method that will return only the selected JPanel?
This is very difficult. By default, JPanels are not focusable (they can't receive keyboard focus).
You could try ascertain the current panel that contains the current focusable component by using KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner(); and using the resulting Component's getParent method, but this is no guarantee, as the focused component may be contained in another container, contained within the container your interested in...
A better idea might be to have some kind of model that connected the buttons or actions to the child panels...?
I have an application where I want that the user is able to choose between normal and advanced settings. Now if the user checks a JCheckBox and the advanced settings should disapper the problem starts.
My idea was to set all unnessecary swing components (JScrollPane, JLabel...) invisible and then find a method of JFrame which fits the window to the VISIBLE components.
My question is if there is such a method?
... and then find a method of JFrame which fits the window to the VISIBLE components. My question is if there is such a method?
Yes, there is such a method, and it is called pack().
This will cascade through the layout managers of all the containers held by the top-level window, asking them to re-lay out their visible components, resizing components to their preferred sizes as based on the components and the layout manager requirements, and eventually resizes the top-level window to fit the containers and their components.
1. You can use setVisible(boolean b), to make the component visible and invisible.
2. You can check that if the component is visible or not using isVisible()
3. You can then use the pack() method, pack() method gives sets the frame size as per need
I think you can wrap the advanced content in a panel (if possible) and remove that panel from frame using this.remove(component) then use this.pack()
and you can do the opposite on showing them, this.add(...) then this.pack() again
I read that JFrame is made of several panes ..what are panes and why is Jframe made of panes ?
And why there is a JPanel while it seems that the JFrame looks exactly like the JPanel but with a menu bar and a close button so what's the need for a JPanel ? Can anybody explain to me clearly the definition and use of those 3 components ?
There are top level containers such as JFrame. These can serve as the main window in which a GUI is built.
Then there are intermediate level containers. These must be placed in other containers, they cannot exist by themselves. They either help you organize components or they add functionality. A JPanel is a very simple container that helps you to organize other components. While a JSplitPane adds the functionality of having two panes that are variable sized.
When you have a complex GUI you may want to use JPanels to organize various areas of your GUI and then add each of the panels to your JFrame.
In Java the Swing API makes use of the Composite Design Pattern. This means that you can compose very complex objects from other objects and still treat the composite objects the same way as the simple objects. So you can put a JPanel into a JPanel and it still behaves like a JPanel.
Think of it like a tackle box (or sewing kit). It is made of a big container. But rather than put many small objects into this big container and make it difficult to manage later you can place some smaller compartments inside the big box. Then hooks and sinkers etc go in the compartments. Its easier to manage. The big box is the JFrame and the compartments are the JPanels.
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.