This week's giveaway is in the JDBC forum.
We're giving away four copies of Java Database Connections & Transactions (e-book only) and have Marco Behler on-line!
See this thread for details.
Win a copy of Java Database Connections & Transactions (e-book only) this week in the JDBC forum!
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Campbell Ritchie
  • Devaka Cooray
  • Knute Snortum
  • Paul Clapham
  • Tim Cooke
Sheriffs:
  • Liutauras Vilda
  • Jeanne Boyarsky
  • Bear Bibeault
Saloon Keepers:
  • Tim Moores
  • Stephan van Hulst
  • Ron McLeod
  • Piet Souris
  • Frits Walraven
Bartenders:
  • Ganesh Patekar
  • Tim Holloway
  • salvin francis

Help with JScrollPane  RSS feed

 
Greenhorn
Posts: 4
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hello everyone !
I've developed an application to draw workflows (basically just boxes connected with arrows but hey ! it's a workflow !). These drawings are placed onto a panel which is placed on a JScrollPane. To enable scrolling when a box is dragged outside the visible area I use the following code:

The above code was placed in the mouseReleased method and worked fine.
I have recently added a save/load feature for the diagrams, so that a user can load a previously created diagram. The problem is the diagram loads properly but even if it was larger than the actual screen the the scrollbars did not appear (which is normal, because no mouseReleased event occured). Then I put the same code with minor modifications in the paintComponent method of the panel:

Now the scrollbars appear but I cannot use them, because the panel keeps on scrolling to the "farthest" box on the panel.
Could anyone help me please, i'm new in swing !
Thanks,
DAN
 
Ranch Hand
Posts: 1535
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Putting your validation code in paintComponent means that it will be called at any time and could result in a undesirable behavior; beyond your control at a minimum.

The JScrollPane checks all of its children and asks for their preferred sizes before it lays them out. So all we need to do is arrange for a suitable Dimension to be returned form our component whenever it is asked for its PS. Whenever changes are made to the GUI (such as adding/removing components or changing graphic boundries) we signal the JScrollPane to lay out its children again by calling revalidate on the child component of its view.
So the technique is:
1 - update size parameters of our component
2 - call revalidate to signal the JScrollPane to do a new layout.

This is taken care of automatically by any scrollpane children who implement Scrollable such as JTextArea.

Here's a demo app. You can drag the rectangle past the boundries of its container to trigger scrollpane updates.

[ January 29, 2004: Message edited by: Craig Wood ]
 
If you open the box, you will find Heisenberg strangling Shrodenger's cat. And waving this tiny ad:
how do I do my own kindle-like thing - without amazon
https://coderanch.com/t/711421/engineering/kindle-amazon
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
Boost this thread!