Question

I’m trying to adapt the following example: http://docs.oracle.com/javase/tutorial/uiswing/examples/zipfiles/components-ScrollDemoProject.zip

The purpose of i want to do is to allow the user to navigate on a picture to a coordinate they choose themselves (but not by mouse). So you have a large picture, and only a small part is showing and this window over the picture moves. This works when using the mouse (see the example of oracle). But i want to do this with coordinates that the user chooses.

In the ScrollablePicture class you can see that it is possible to move the picture by dragging the mouse :

public void mouseDragged(MouseEvent e) {
    Rectangle r = new Rectangle(e.getX(), e.getY(), 1, 1);
    scrollRectToVisible(r);
}

I tried to do the same, so i added this method underneath the mouseDragged function :

public void moveMap(float X, float Y){

    Rectangle r = new Rectangle((int)X,(int) Y, 1, 1);
    System.err.println("Scroll to "+ r.x);
    scrollRectToVisible(r);
}

When i look at my output i can see that i get coordinates in the method. But the window is not scrolling. My question now is: Why isn’t it scrolling and how do i fix this ?

Ps: It has nothing to do with the values. Because i tried with fixed numbers in both of the function e.g :

Rectangle r = new Rectangle(2000,2000, 1, 1);

It worked in the mouseDragged function but not in the moveMap function

Answer 1

Your code works fine.

Here is how you can test it:

In the class ScrollDemo make the pictrue public:

public ScrollablePicture picture;

In createAndShowGUI() change type of the variable JComponent newContentPane to:

ScrollDemo newContentPane = new ScrollDemo();

After frame.setVisible(true); call your moveMap method:

frame.setVisible(true);
    
newContentPane.picture.moveMap(1, 250);

Now you can see that the picture is scrolled down so the pixel at (1, 250) is visible:

Left side: without the moveMap(1, 250); call. Right side: with the call. – The moment after start of the application.