The Viewers tab in a flow editor contains a table that displays the names of the work item viewers that have been added to the flow, as well as the Generic viewer, which appears on the tab automatically. By default, the Generic work item viewer designated as the default viewer.
To select a different viewer as the default viewer, select the Default option for that viewer. If a viewer that will be generated from a template has been configured and added to a flow, but that viewer has not yet been generated, then that viewer cannot yet be used because the viewer file does not yet exist. If a viewer still needs to be generated, then a check mark appears in its Needs Gen check box.
Also, if you have successfully generated a viewer, but you make further changes to the viewer without regenerating in the Work Item Viewers dialog, then the Needs Gen check box will be selected for that viewer as well.
To quickly generate or regenerate any viewer that meets either of these conditions, click on that viewer’s row to select it (you can Shift-click or Ctrl-click to select multiple viewers), and then right-click on the chosen viewer and select Regenerate from the shortcut menu.
After a viewer has been generated successfully, the Publish check box in the far-right column of the Viewers tab table becomes selected. The next time the flow is saved, the viewer is published to the Web server.