Create Downloads in a Fixed Category
It is quite possible to create a Download in the Front End with a fixed Category that the User cannot change.
But note that the Category field will still be be shown in the Download creation form. However it is not changeable.
First assume that a specific Joomla User Group has been set up for those users who are to upload to a fixed category. In this example we are using User Group 'AAA-UG', whose parent UG is Registered. Also set up a view Access Level called say 'AAA-view' with 'AAA-UG' as its only member - but it may be useful to add in the super users UG.
Now suppose that the jD sub category into which a member of 'AAA-UG' is able to create a Download is called 'AAA-cat'. It is important of course to ensure that 'AAA-cat' has at least Create & Edit permissions for the 'AAA-UG' user group.
The Next step is to create a menu item, in an appropriate menu, that is a jD menu item type 'Single Category', and of course give it a suitable title (left hand picture).
Set the Access level to 'AAA-view' (centre picture), and on the Options tab click on the Fixed Category radio button and from the pull down select category 'AAA-cat' (right hand picture).
Setting the view Access to 'AAA-view' means that only members of the 'AAA-UG' will see the menu item.
The final stage is setting up 'AAA-UG' in the jD User Groups Settings. Obviously one needs to set the Ranking to a sufficiently high level, say 135. The relevant questions are readily 'ticked' in the 'Group Creation/Editing Settings' tab.
As noted the Display Add/Upload icon may or may not be required.
In some cases you may not wish to include the Menu Item 'Create Download in AAA' in the visible set even if it is only shown to users in the 'AAA-UG'.
In this case the Menu Item 'Create Download in AAA' is still required but may be placed in a hidden menu. The Add/Upload button will produced the same result when a member of the 'AAA-UG' is logged in with the selected category being displayed in an uneditable field as shown below.
The Create Download menu item, or the Add button, will now show the name of the fixed Category as illustrated opposite. The field is not editable so members of the AAA-UG cannot change it.
The same applies when the Download is edited from the Front End.
Colin Mercer June 2018