Java:

Emyr

I'm creating an image viewer, and have extended JComponent for the viewing area.

This component is placed in a JScrollPane. To make sure the scrollbars appear, I need to tell it that its contents are big...

Image i = Toolkit.getDefaultToolkit().getImage(path);
int height = i.getHeight(null);
int width = i.getWidth(null);
System.out.println(width + " " + height); //some debugging help...
previewArea.setImage(i);
previewArea.setPreferredSize(new Dimension(width,height));

My problem is that getWidth and getHeight nearly always return -1 (i.e. size not yet known). What should I give them as the "ImageObserver" in order to make them wait?

just call setHorizontalScrollbarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS) on the scrollpane and the same for vertical scrollbar.

Emyr

That makes it show scrollbars, but they don't work because the extended JComponent isn't making itself big enough to stretch the viewport...

What are you wanting? Are you wanting the component to be larger or are you wanting the scroll bars to work? If you are wanting the component to be larger I would suggest overriding the getWidth and getHeight methods of the component if they are not getting the correct width and height of the image.

BTW:

I wrote an image manager once that loaded images into memory and this problem didn't occur for me. I think I used ImageIcon and then if I needed the actual image I just called icon.getImage(). You might want to try that, but I don't remember if that's exactly how I did it and I don't have the code with me.

Emyr

I have an extended Jcomponent in a scrollpane.

in the JComponent's paint method, I paint the current image onto the canvas, using AffineTransforms to allow rotation and zooming (rotation isn't supported by ImageIcon as far as I can see.

I need to define the component's size for the scrollpane to think there's something that needs to be scrolled.

I don't think it'll matter whether I override the standard JComponent's getWidth function to hardwire it to the Image.getWidth finction, or if i set the component's size normally, because I still don't know the image's size (it returns -1 becuase it doesn't know)

see?

Emyr

I've avoided the getWidth returning -1 problem by moving this section to inside the Paint method...

<font face="Geneva,Arial,sans-serif" size="2">So my problem is now that neither using setPreferredSize(Dimension) nor setMinimumSize(Dimension) will make the JScrollPane realise that its contents are actually quite big... </font>

Skurry

Try calling revalidate() on the image or its container after the image has been loaded or transformed.

Emyr

My extended JComponent now implements scrollable, and works, except that if I stretch the window so it's bigger than the current image, it refuses to paint any future images; the dimensions and other data come up in the right places, but the image area remains grey.

GizmoC

In your paint method, call super(g); (g being your Graphics object). Lemme know if that works.

malfist

edit: bah

Emyr

D:\Java>javac *.java
MyPaintingArea.java:13: call to super must be first statement in constructor
                super(g);
                     ^
1 error

Skurry

I think he meant super.paint(g)

VGR

The object you want to pass is previewArea:

int height = i.getHeight(previewArea);
int width = i.getWidth(previewArea);

However, you will never be guaranteed that getWidth or getHeight will return a nonnegative value, because the image is being loaded in another thread.

It's possible to use a MediaTracker to wait for the information to become available. However, if you're using Java 1.4 or later, there's a much easier solution:

import javax.imageio.ImageIO;
...
BufferedImage i = ImageIO.read(new File(path));

This call will not return until the image is fully loaded. And it returns a BufferedImage, so you can call the getWidth() and getHeight() methods which take no arguments.