I'm using a custom JLayeredPane.
I have several Shapes which needed to be drawn on different layers in the JLayeredPane.
To test this I create a JPanel and ask its graphics. Then I draw a test rectangle on that JPanel (preparing the graphics) and in my paintComponent method from the JLayeredPane I finally draw everything. But this fails (NullPointerException).
public class MyCustomPanel extends JLayeredPane {
// test
JPanel testpane;
Graphics g2;
// test
// constructor
public MyCustomPanel() {
testpane = new JPanel();
this.add(testpane, new Integer(14));
g2 = testpane.getGraphics();
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g2.drawRect(10, 10, 300, 300);
}
}
// run:
//Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
// at view.MyCustomPanel.paintComponent(MyCustomPanel.java:65)
Why can't I draw on such a JPanel from within my JLayeredPane? I can draw directly on my JLayeredPane from within my paintComponent method but that's on the default Panel from the JLayeredPane. I need to create and draw on several layers which are added in my JLayeredPane.
What am I doing wrong? :s
You should use g2 casting the Graphics that is passed to you:
Graphics2D g2 = (Graphics2D)g;
Why don't you try decoupling things?
class InnerPanel extends JPanel
{
public void paint(Graphics g)
{
Graphics2D g2 = (Graphics2D)g;
g2.drawRect(....);
}
}
class MyLayered extends JLayeredPane()
{
MyLayered()
{
this.add(new InnerPanel(), 14);
}
}
this makes more sense..
Also because you are trying to do something that doesn't agree with Swing behaviour.
Swing will care by itself to call the appropriate paint methods over things that must be displayed, and to go with this protocol you should tell Graphics objects what to draw when Swing asks it to your objects (calling the paint) method, not when you want to do it.
In this way whenever Swing wants to draw your JLayeredPane you just draw things on a Graphic object of other things without considering that Swing will call their appropriate methods when it's the right time to do so.
In conclusion: you can't draw something on a Graphic object when you want it. You can do it just inside methods invoked by Swing, because otherwise Graphics of these objects doesn't mean anything
The variable g2 is probably null because you set it in the constructor, not when drawing. Instead, use the "g" that was passed in.
You can only get a legitimate Graphics from a component that is currently being painted. Otherwise, it's not valid. At the point you're requesting it, the MyCustomPanel() isn't being displayed, and neither is testpane.
Related
In java awt or swing when you want to change painting of some component you usually have to override the method paint(Graphics g) (in awt) or paintComponent(Graphics g) (in swing).
This is usually (maybe allways - I'm not sure) done when you are creating the component for example:
JPanel jPanel = new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
//... my implementation of paint, some transfromations, rotation, etc
}
};
Imagine that you have container of components which could for example consists of some JLabels, some JTextFields, some image. Which will be all put on one component.
By container I mean you have some list or map with ids or some similar structure in which are all components you will put on one JFrame.
The question is if I can change the painting method after creating with all of the components which are in this list in the moment when all of them are already created. For example I want do the rotation action (rotate), which is defined in Graphisc2D, with all of them.
So basicaly what I want is that I throught the list of componets I have and say:
"All of you (components) which are in the list will be rotated by some angle". Is that possible? If yes how?
Edit:
This is my not correctly working solution:
graphicalDisplayPanel = new JPanel() {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g2d = (Graphics2D) g;
g2d.rotate(Math.PI, anchorx, anchory);
}
#Override
public void paintChildren(Graphics g) {
super.paintChildren(g);
Graphics2D g2d2 = (Graphics2D) g;
g2d2.rotate(Math.PI, anchorx, anchory);
}
};
JFrame jFrame = JFrame();
// ... setting dimension, position, visible etc for JFrame, it works correctly nonrotated
jFrame.setContentPane(graphicalDisplayPanel);
I have not tested this, but it seems like it would work. A JComponent's paint() method calls:
paintComponent(co);
paintBorder(co);
paintChildren(co);
where co is a Graphics object. In theory you create an image, retrieve the graphics object and then pass that into paintChildren(). you will have to call paintComponent() and paintBorder() yourself, if you do this. Then, just rotate the image and draw it into your component. You may have to crop the image or resize your component accordingly for this to work. It might look something like this:
BufferedImage myImage;
#Override
public void paint(Graphics g){
myImage = new BufferedImage(getWidth(), getHeight(), BufferedImage.TRANSLUCENT);
//using a transparent BufferedImage might not be efficient in your case
Graphics myGraphics = myImage.getGraphics();
super.paintComponent(g);
super.paintBorder(g);
super.paintChildren(myGraphics);
//rotation code here
// ...
//draw children onto your component
g.drawImage(myImage, 0, 0,getWidth(), getHeight(), null);
}
I hope I didn't make any mistakes, please let me know if this works.
So basicaly what I want is that I throught the list of componets I have and say: "All of you (components) which are in the list will be rotated by some angle".
If you want to rotate panel and therefore all the components on the panel as a single using then you need to do the custom painting in the paintComponent() method.
If you want to rotate, for example, individual images that each have a different angle of rotation then you can again do this in the paintComponent(...) method and change the angle for each component.
Or, in this second case you can use the Rotated Icon class. In this case the Icon is just added to a JLabel. Then you can change the degrees of rotation and repaint the label, so there is no custom painting (except in the Icon itself).
I was wondering if someone could explain how/why paintComponent() is called right after all the statements in main() are run. The reason I am confused is that there is no explicit call to painComponent() but it is run regardless.
// JComponent is a base class for custom components
public class SimpleDraw extends JPanel {
public static void main(String[] args) {
SimpleDraw canvas = new SimpleDraw();
JFrame f = new JFrame("SimpleDraw"); // jframe is the app window
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setSize(400, 400); // window size
f.setContentPane(canvas); // add canvas to jframe
f.setVisible(true); // show the window
}
// custom graphics drawing
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g; // cast to get 2D drawing methods
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, // antialiasing look nicer
RenderingHints.VALUE_ANTIALIAS_ON);
g2.setStroke(new BasicStroke(32)); // 32 pixel thick stroke
g2.setColor(Color.BLUE); // make it blue
g2.drawLine(0, 0, getWidth(), getHeight()); // draw line
g2.setColor(Color.RED);
g2.drawLine(getWidth(), 0, 0, getHeight());
}
}
Here is a decent little write-up on how paintComponent is handled.
Excerpt:
Who calls paintComponent
... This method is called because the user did
something with the user interface that required redrawing, or your
code has explicitly requested that it be redrawn. Called automatically
when it becomes visible When a window becomes visible (uncovered or
deminimized) or is resized, the "system" automatically calls the
paintComponent() method for all areas of the screen that have to be
redrawn. Called indirectly from a user-defined listener via repaint() ...
There's more in the write-up as well as some reference links, which, unfortunatelly, are all broken.
I also found this blog post which discusses painting/drawing in Java from a very basic point of view. Check out the first paragraph:
Why do we put all our graphical drawing code into a paintComponent()
method? It seems odd, since it would seem we should be able to simply
stick some simple graphics commands into our main() method in a Java
application and just get the drawing done. Where does paintComponent
come from? If we never call it in our code, how does it get executed?
In the Java docs you actually have to read up on paint to start getting an idea of what going on. The paintComponent documentation is not very helpful.
I am trying to make a small paint program. I am drawing objects over a JPanel which is on top of JFrame (I am using Netbeans 6.9). I have some basic functionality like font, line and fillRectangle. I am using the standard method to draw which is to override paintComponent().
class .... extends JPanel
{
#Override
void paintComponents(Graphics g)
{
.......
}
}
The problem is that when I draw a text,line over a region then it is drawn behind it rather than on top of it. Basically I want to draw objects on top of all other objects that have previously been drawn on the JPanel. I really do not want to switch to other types of layered pane. One very naive method will be to undo every object and paint them in reverse order (last one first).
You will need to override paintComponent(Graphics g) and do not forget to call super.paintComponent(Graphics g);
class .... extends JPanel
{
#Override
protected void paintComponent(Graphics g)
{
super.paintComponent(g);//honor paintComponent an call super to draw other components that were added to the JPanel
.......
}
}
You may also need to override getPreferredSize(..) of JPanel and return an appropriate size so the JPanel will be visible:
class .... extends JPanel
{
#Override
public Dimension getPreferredSize()
{
return new Dimension(300,300);
}
}
EDIT:
Depending on what you are doing you may also want to have a look at the GlassPane which will allow you to set a transparent pane over the entire JFrame window and can be painted too, which will cause the graphics to be drawn above all others like so:
This is an old question, but I had the same problem and solved it by overriding paintChildren(Graphics g) instead of paintComponent.
As the Oracle documentation states, the order of execution for the three paint methods is:
protected void paintComponent(Graphics g)
protected void paintBorder(Graphics g)
protected void paintChildren(Graphics g)
So, paintChildren(g) is run last, which means whatever we draw inside it is drawn on top of all previously drawn components.
I have a Problem:
I'm rendering a BufferedImage in a JFrame. Then i add a JButton to the same frame.
when i try to make the button transparent, the button becomes transparent, but disregarding its actual position, its always transparent like it is stuck in the top left corner of the frame.
I testet some different methods to make the button transparent, always with the same result.
any ideas?
thanks
public class TestPanel extends JPanel {
public TestPanel(){
JButton foo = new JButton("test");
foo.setBackground(new Color(0, 0, 0, 0));
foo.setBounds(20, 100, 300, 50);
this.add(foo);
}
public void paint(Graphics g){
Graphics2D g2 = (Graphics2D) g;
g2.drawImage(ImageFactory.getImg(), 0, 0, null); //get a BufferedImage
g2.dispose();
}
}
I see several problems, even if I'm not sure on which of them cause your problem.I try to list them in order:
Your TestPanel doesn't specify a LayoutManager (I hope you are specifying it somewhere else in your code).
You are extending a JPanel without call super paintComponent method (don't use paint). You should do this before anything else in your paintComponent method:
public void paintComponent(Graphics g){
super.paintComponent(g);
}
remove the dispose method call. You must not destroy your graphic object.
EDIT:
this is a problem:
foo.setBounds(20, 100, 300, 50);
you are trying to explicitly set the bounds of your JButton. You shouldn't do that. If you are using a LayoutManager it probably ignore this directive. If you are using a null layout this could be a problem too.
Several problems
it's wrong to override paint, instead override paintComponent
the button has a fully transparent background but returns true for opaque, thus fooling the paint mechanism
it's wrong to dispose the Graphics passed in as parameter
working code (Edit: accidentally removed the transparent color-setting line, fixed)
public TestPanel(){
JButton foo = new JButton("test");
foo.setBackground(new Color(0, 0, 0, 0));
foo.setOpaque(false);
foo.setBorder(BorderFactory.createLineBorder(Color.RED));
this.add(foo);
}
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.drawImage(ImageFactory.getImg(), 0, 0, null); //get a BufferedImage
// g2.dispose();
}
As others already noted: LayoutManagers are a must in Swing/AWT - not using them makes the ui code brittle and hard to maintain.
setBound() will work only if you have set your layout to null. Your code does not say anything like that.
Now, the default layout manager of JPanel is FlowLayout. By default, this layout manager will arrange your components from left to right then top to bottom.
Now, to make your code work as expected. Add this line inside your constructor: setLayout(null).
But remember, setting the layout to null is a very poor practice.
Also, the points Heisenbug has mentioned are very worthy. Try to follow them.
Ok I'm wondering why the code below will not display the JLabel.
MyPanel is getting added correctly to a JFrame and everything because it all displays but will not draw the JLabel. Any help is appreciated.
public class MyPanel extends JPanel {
private Root root;
...
public void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
root.paint(g2);
}
}
class Root {
private Node1 node1;
...
public void paint(Graphics g) {
node1.paint(g);
}
}
class Node1 {
...
public void paint(Graphics g) {
JLabel jtp = new JLabel();
jtp.setLocation((int) x, (int) y);
jtp.setSize((int) width, (int) height);
jtp.setLocation(40, 40);
jtp.setSize(40, 40);
jtp.setText("Hello world");
//jtp.setVisible(true);
jtp.paint(g);
}
}
I suggest that you don't add Components to a Container in a paint method as 1) you do not have absolute control when or even if a paint method will be called and 2) paint and paintComponent have to be as blazing fast as possible, and this is not the time or place to update a GUI. 3) Since paint is often called many times, you will be adding components many times to your container, and all out of your direct control.
Also, while you're adding a component into Root (whatever Root is since it doesn't extend JComponent, JPanel, or similar) in the paint method, the Root object is never added to anything else that I can tell, and so it makes sense that nothing "added" to a component that is not added eventually to a top-level window will be visible.
Bottom line: I think you need a gui re-design as your solution. If you tell us more about it we can help you with it. Next we'll need to talk about use of layout managers and why setting absolute position and sizes of components is usually frowned on.
If anything I say is confusing, please ask for clarification, or if anything is wrong, please help me correct it!
You should not create your JLabel inside the paint method - instead, create it once when initializing your MyPanel. Your label is kind of a renderer component for your nodes, which in principle is a good thing. You may look how the renderers for JTable, JList, JTree work.
In your case, don't set the location of your label (it does not change anything, since it's paint-method expects its graphics object to be oriented by its own upper left corner), instead translate the Graphics-context:
Graphics copy = g.create((int)x, (int)y, (int)width, (int)height);
jtp.paint(copy);
(Graphics2D has some more fancy methods for shifting, rotating, scaling the context, too.)
Other than this, I don't see any problems. Make sure your Node1.paint() method gets actually called by putting some System.out.println() in there.