I'm searching for a way to make a link to add a new item in a category.
For example I want to make a link in a article that takes you to the form for adding a article where the category is already set.

Something like "/index.php/component/k2/item/add?tmpl=component&categoryid=3" is not working.

I think this will have to be done with access control such that..a paticular user can only post in paticular k2 categories. Other than that...I am not to sure it can be done without creating new kind of menu links for k2 (or joomla to that matter).

Usually people use a content submission form and admins direct the article to the category it needs to go into.

Use the Submit item Button in Category Listing itself (activate in Backend) or use the nw K2_user module with the render Menu Function. plz read the 2.5 + 2.5.1 Changelog in Blog

I solved this part indeed by adding a hidden menu-item and making a link to that id. Thanks Thorsten Renz!

<a class="modal" href="/index.php?option=com_k2&view=item&task=add&tmpl=component&Itemid=163" rel="{handler:\'iframe\',size:{x:990,y650}}">>> voeg nieuws toe</a>

But now it seems like I'm missing some javascript for getting a nice popup windown to make a new item.

What I get now is a full page form. And when I close it, it brings me to my site again but then to a empty page.

Any help is greatly appreciated!

After a many hours fight I solved the problem. But don't ask me how. I can not tell... But it works!!!