Gwt Image original size - gwt

Question

I use an Image object to load a png image as a thumbnail by calling its setPixelSize() method to resize the image. I also need to retrieve the original size of the image as integers at some point. How can I get the original sizes (width, height) of the image?
ok i found a workaround: I use a dummy container (SimplePanel) and load the image without scaling save its real dimensions and then remove the container from the parent and discard the new Image object. I don't know if this a good workaround, but it works. Although i would like to know if there is another way...
problem of the workaround: I have a droplist from which i can select logical folders (which contain images). When i select a new folder, and the new set of images is loaded on display, then i get 0 for width and 0 for height.
private void getTrueSize(String fullUrl) {
Image trueImage = new Image();
this.tstCon.add(trueImage);
trueImage.setUrl(fullUrl);
this.trueHeight = trueImage.getHeight();
this.trueWidth = trueImage.getWidth();
//this.tstCon.remove(trueImage);
//trueImage = null;
GWT.log("Image [" + this.imgTitle + "] -> height=" + this.trueHeight + " -> width=" + this.trueWidth);//
}

Answer 1

Extend the Image class and implement onAttach() method. This method is called when a widget is attached to the browser's document.
public class Thumb extends Image {
public Thumb(){
super();
}
protected void onAttach(){
Window.alert(getOffsetHeight()+" "+getOffsetWidth()); //this should give you the original value
setPixelSize(10,10); // this should be the visible value
super.onAttach();
}
}
if this doesn't work, try implementing onLoad() instead of onAttach(), since onLoad() will be called after the image is added to DOM so that it definately should work.

Answer 2

Its the easiest way to create a new hidden Image (placed absolute outside the viewport) and read the size. There is a JavaScript lib that can read the exif data of the image but this would be overkill in this case.

Answer 3

Read naturalHeight and naturalWidth of the image element after image load.
public Panel() {
image = new Image();
image.addLoadHandler(this::onLoad);
}
private void onLoad(#SuppressWarnings("unused") LoadEvent event) {
origImageWidth = getNaturalWidth(image);
origImageHeight = getNaturalHeight(image);
}
private static int getNaturalHeight(Image img) {
return img.getElement().getPropertyInt("naturalHeight"); //$NON-NLS-1$
}
private static int getNaturalWidth(Image img) {
return img.getElement().getPropertyInt("naturalWidth"); //$NON-NLS-1$
}