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Lines disappear when scrolling

 
Sharon whipple
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Hi all,
I am drawing lines on JComponent/JPanel wrapped in Jscrollpane (along with two JTables) the lines connect the rows of the left and right tables.

When I scroll down, the lines erased by the top part of the container,
So i tried to use the repaint method and now the lines disperses completely.

please advise


Here is the canvas:



And this is the ScrollBar listener:

 
Craig Wood
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There are so many ways to get into trouble with drawing that it's difficult to
know where to start with what you've presented.
Some comments:
Looks like you are using custom Point and Line classes. I wonder what's going on
in the Line class: could you be changing the line locations with each of the p1.setX(p1.getX() +...–type calls?

I experimented a bit with the getComponentGraphics method and it seems to
alter the graphics context, at least the color, during the drawing of the lines.
Maybe you are trying to draw only the parts of the lines that need re-drawing.
Swing will do this for you automatically (double–buffering).

The scrollPane will automatically repaint the graphics located within its view
extent.
Here's an idea:
 
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