Q:

Definite article "the" introducing the subject of a sentence

In a tutorial on Qt Quick I have the following line in a paragraph describing the main screen:
ItemDelegate wrapper contains all fields on the main screen and the detail screen. 
My question is: is this correct ?  Or do I need to put "The" before ItemDelegate.

A:

In your example sentence, the missing article makes it reads like headlinese.

In headlinese, used in the construction of headlines, sentences are constructed without articles or other elements in order to reduce their space. (Or at least that's how the practice started.) This is often accompanied by changing verbs into the present tense.
For example:

A man jumped from a building yesterday. (Regular sentence.)
  Man jumps from building. (Newspaper headline.)

If you want your sentence to read more naturally, you can make the subject plural, add an article, or even (although this would be non-standard) use a possessive:

ItemDelegate wrappers contain all fields on the main screen and the detail screen.
The ItemDelegate wrapper contains all fields on the main screen and the detail screen.
An ItemDelegate wrapper contains all fields on the main screen and the detail screen.
ItemDelegate's wrapper contains all fields on the main screen and the detail screen.  

Which version you choose would depend on the context and your own preference.

As a note, all fields is an elliptical version of all of the fields and could be considered a minor form of headlinese itself.
To avoid that entirely (it's purely a matter of style), something like the following could be used instead:

ItemDelegate wrappers contain all of the main screen and detail screen fields.  

