How to add a vertial scrollbar in Canvas?

Question

I am developing a Java ME application using Canvas. The details displayed on the Canvas are plentiful, so I need to scroll down the screen to view the further details.

But how can I add a vertical scrollbar on a Canvas?

Answer 1

I think that the scrollbar should be drawn inside the paint method. And you implement the keyReleased method when clicking the arrow of the scrollbar. To implement the scrolling I would prefer call repaint(); and I will manage the paint method with boolean or some other type of private variable.

Answer 2

Consider your canvas as the source and the scroll bar as destination use the following formula to find the scroll bar position

Target point X co-ordinate: tX = taX + ((tW * (sX - saX)) / sW)

Target point Y co-ordinate: tY = taY - ((tH * (saY - sY)) / sH)

saX : Source axis start X coordinate

saY : Source axis start Y coordinate

sW : Souce Width

sH : Source Height

taX : Target axis start X coordinate

taY : Target axis start Y coordinate

tW : Target Width

tH : Target Height

The target height would be the height of the canvas. You must draw the scroll bar as the topmost element.