Before looking at the sample application, this chapter looks at the function that gives applications access to Viewer: the MVAPI function.
MVAPI has the following syntax:
extern BOOL FAR PASCAL MVAPI (hwndMain,lpszMvbFile,usCommand,ulData)The hWnd parameter identifies the window requesting access to Viewer. Applications use this identifier to keep track of which applications have requested access to Viewer.
The lpszMvbFile parameter specifies the name (with optional path) of the Viewer file being accessed.
The usCommand parameter either specifies the type of search the application uses, or tells Viewer that the application no longer requires access. In our sample, usCommand usually has the constant value cmdMacro, indicating that the application wants to execute a Viewer command. However, usCommand can also take any of the following values:
| Value | Action |
| cmdContents | Displays the Viewer contents topic |
| cmdFocus | Gives Viewer the focus |
| cmdId | Displays a particular Viewer topic identified by a context string |
| cmdIdPopup | Displays a popup window containing a topic identified by a context string |
| cmdKey | Displays a topic associated with a keyword |
| cmdNewInstance | When used in an expression with the binary-OR operator (| ) and any other command |
| cmdPartialKey | Brings up the Index dialog box and selects the keyword closest to a specified string |
| cmdTerminate | Informs the Viewer application that Viewer is no longer needed |
The ulData parameter specifies the topic the application requests Viewer to display. The format of ulData depends on the value of usCommand that the application passes in the MVAPI call. The following table describes the format of ulData for each value of usCommand:
| usCommand Value | ulData Format |
| cmdContents | Ignored; applications should set to 0L |
| cmdFocus | Ignored; applications should set to 0L |
| cmdId | A far pointer to a string containing the context string of the topic to be displayed |
| cmdIdPopup | A far pointer to a string containing the context string of the topic displayed in the popup window |
| cmdKey | A far pointer to a string containing the keyword for which the topic is displayed |
| cmdMacro | A far pointer to a string containing the Viewer command |
| cmdNewInstance | Ignored; this value of usCommand used only with other commands |
| cmdPartialKey | A far pointer to a string used to select a keyword |
| cmdTerminate | Ignored; applications should set to 0L |