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Inside Macintosh: Macintosh Toolbox Essentials

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MyFilter

When you use GetSpecificHighLevelEvent (GetSpecificHighLevelEvent) to search the high-level event queue of your application for a specific event, you supply a pointer to a filter function. GetSpecificHighLevelEvent calls your filter function once for each event in the high-level event queue until your filter function returns true or the end of the queue is reached. Your filter function can examine each event and determine whether that event is the desired event. If so, your filter function should return true .

Here's how you declare the filter function MyFilter :

pascal Boolean MyFilter (void *contextPtr,
                                         HighLevelEventMsgPtr msgBuff,
                                         const TargetID *sender);


contextPtr

The address of data that specifies the criteria your filter function should use to select a specific event. For example, you can specify in the contextPtr parameter the address of a reference constant to search for a particular event, the address of a target ID structure to search for a specific sender of an event, or the address of an event class to search for a specific class of event.

msgBuff

A pointer to a structure of type HighLevelEventMsg , which provides: the event record for the high-level event and the reference constant of the event. The HighLevelEventMsg data type is described in "The High-Level Event Message Structure" .

sender

The address of the target ID structure of the application that sent the event. The target ID structure is described in "The Target ID Structure" .