I always do
Jbutton.setEnabled(false);
Jbutton.update(Jbutton.getGraphics());
when disabling a button, but someone told me that Jbutton.update(Jbutton.getGraphics()); shouldn't be used, or at least not used that way. Why? is it not efficient? Is it incorrect? Should I change my method?
Shouldn't use getGraphics() on Jbutton.update,
Actually it's wider than that. Programmers should never use getGraphics on any JComponent (or AWT Component) or the same for Swing (and AWT) windows.
Why?
Because the painting methods are called by the API, whenever it feels the need to repaint (e.g. restoring a window from minimized, moving another window on top of or away from the window, bringing it to front ..).
So any call that uses getGraphics is 'transient'.
[ The correct way to do custom painting is mentioned in Holger's comment, but that wasn't the question. ]
Related
I've seen it written on this site a number of times (such as here, and here) that you mustn't call setVisible(true) before adding components to a JComponent, but I haven't seen an explanation, and information on the internet seems scarce.
Why is this the case, and what happens if you break the rule?
You're not breaking anything if you call it first, but you will probably then need to call it again if you've added anything. Else Swing won't render the added components. You need to have the JVM call the JFrame's paint(...) method to have the JFrame's components rendered, and setVisible(true) will ask the JVM to do just this. If you've ever add components after calling setVisible(true) and don't see the components, you'll find that they'll "materialize" if you re-size the JFrame. This is because re-sizing it causes the operating system to ask Swing to repaint the GUI, and this will result in paint(...) being called.
Note that if you add a component after creating your GUI, you can call revalidate() and often repaint() on its container to get the new component laid out correctly and then rendered. The repaint() will definitely be necessary if the change in components involves a deletion, or a component being drawn where another component was visualized previously.
A book suggestion that I highly recommend: Filthy Rich Clients buy Guy and Haase. Just buy it! You won't regret the purchase.
Amplifying on #Hovercraft's helpful analysis, you may also have to re-pack() the enclosing top-level container. This example, which adds elements to a JList after setVisible(), may illustrate the trade-offs.
I've seen it written on this site a number of times (such as here, and here) that you mustn't call setVisible(true) before adding components to a JComponent, but I haven't seen an explanation, and information on the internet seems scarce.
Why is this the case, and what happens if you break the rule?
You're not breaking anything if you call it first, but you will probably then need to call it again if you've added anything. Else Swing won't render the added components. You need to have the JVM call the JFrame's paint(...) method to have the JFrame's components rendered, and setVisible(true) will ask the JVM to do just this. If you've ever add components after calling setVisible(true) and don't see the components, you'll find that they'll "materialize" if you re-size the JFrame. This is because re-sizing it causes the operating system to ask Swing to repaint the GUI, and this will result in paint(...) being called.
Note that if you add a component after creating your GUI, you can call revalidate() and often repaint() on its container to get the new component laid out correctly and then rendered. The repaint() will definitely be necessary if the change in components involves a deletion, or a component being drawn where another component was visualized previously.
A book suggestion that I highly recommend: Filthy Rich Clients buy Guy and Haase. Just buy it! You won't regret the purchase.
Amplifying on #Hovercraft's helpful analysis, you may also have to re-pack() the enclosing top-level container. This example, which adds elements to a JList after setVisible(), may illustrate the trade-offs.
I create a little program that load a frame in which I added some panels.
When I click on some button it should show some panels and hide other.
I'm experiencing some difficult to do it, even because I don't really figure out the diference between setVisible(true), repaint() and validate() (that some friends of mine suggested to me).
I hope you can make me to understand!
Thank you.
Carefully read the API for JComponent. The usages are:
setVisible - it will hide or show your component altogether. If you set it as false, you won't see it at all.
repaint() - is called when the actual pixels need to be redrawn, this is done automatically. It's used, for example, when you move a window on top of your GUI and then move it away. The part that was covered needs to be redrawn.
validate() - you should call this when the layout of your GUI has changed and you need the manager to replace and redraw your GUI.
It's a bit more complicated than that, so again, carefully read the API.
setVisible(true): sets the component so that it's visible.
repaint(): calls the paint method on the component.
revalidate(): updates the component based on the root component
I've seen it written on this site a number of times (such as here, and here) that you mustn't call setVisible(true) before adding components to a JComponent, but I haven't seen an explanation, and information on the internet seems scarce.
Why is this the case, and what happens if you break the rule?
You're not breaking anything if you call it first, but you will probably then need to call it again if you've added anything. Else Swing won't render the added components. You need to have the JVM call the JFrame's paint(...) method to have the JFrame's components rendered, and setVisible(true) will ask the JVM to do just this. If you've ever add components after calling setVisible(true) and don't see the components, you'll find that they'll "materialize" if you re-size the JFrame. This is because re-sizing it causes the operating system to ask Swing to repaint the GUI, and this will result in paint(...) being called.
Note that if you add a component after creating your GUI, you can call revalidate() and often repaint() on its container to get the new component laid out correctly and then rendered. The repaint() will definitely be necessary if the change in components involves a deletion, or a component being drawn where another component was visualized previously.
A book suggestion that I highly recommend: Filthy Rich Clients buy Guy and Haase. Just buy it! You won't regret the purchase.
Amplifying on #Hovercraft's helpful analysis, you may also have to re-pack() the enclosing top-level container. This example, which adds elements to a JList after setVisible(), may illustrate the trade-offs.
I have a JPanel which contains a lot of child components. While updating\adding new components to the parent JPanel I'd like to prevent it from repainting, how can this achieved?
Try RepaintManager.currentManager(component).markCompletelyClean(component). It will prevent the component from repainting. You might need to do this after each time you add new components.
setVisible(false)
update
setVisible(true)
you could try by using setIgnoreRepaint(boolean value) but it's a typical swing feature that can or cannot work (mainly because it depends from AWT so you never know).
Otherwise you could override the paint method by using a flag that simply makes the methor return without calling super.paint(). (actually overriding paintComponent should be the right choice)