The Screen Object Model

The architecture of Attachmate Verastream SDK for Unisys and Airlines revolves around the Screen object model. Once you have acquired a configured Screen object using the SDK SessionLoader object, the Screen object allows you to interact with a 3270, 5250, T27, UTS, ALC, or VT host session.

Note that the host-specific Screen objects do not reside at the top level of the SDK object model, but are implementations of a generic Screen object interface type. However, you can only interact programmatically with a host session using the Screen object that coincides with your host type.

Screen Objects

The Screen object provides access to the presentation space for reading from and sending data to the host. Screen objects are host-dependent, and there is a unique screen type for each type of emulation: 3270 (ScreenTn3270), 5250 (ScreenTn5250), ALC (ScreenAlc), T27 (ScreenT27), UTS (ScreenUts), ALC (ScreenAlc), and VT (ScreenVt).

The Screen objects all implement the IScreenUPG interface (as illustrated below), which defines all of the methods that are used to establish the host connection and perform host operations via that connection.

Screen object hierarchy

Screen Object Packages

Attachmate Verastream SDK for Unisys and Airlines provides the following Screen object packages for creating custom host access applications:

These packages are documented in the Javadoc and .NET reference guides.

Screen object Package name
ScreenTn3270 com.attachmate.UPG.ScreenTn3270
ScreenTn5250 com.attachmate.UPG.ScreenTn5250
ScreenT27 com.attachmate.UPG.ScreenT27
ScreenUts com.attachmate.UPG.ScreenUts
ScreenVt com.attachmate.UPG.ScreenVt
ScreenAlc com.attachmate.UPG.ScreenAlc
Related Topics
Requesting a Screen Object
Host Connection Types Supported