Descriptor Records

Applications must use Apple Event Manager functions to create and send an

Apple event. The Apple Event Manager constructs its own internal data

structures to contain the information in an Apple event. To gain access to this

data, the target application also must use Apple Event Manager functions.

Neither the sender nor the receiver of an Apple event can directly manipulate

the data inside an Apple event; each must rely on Apple Event Manager

functions to do so. This section describes the data structures that the

Apple Event Manager uses to create and to process Apple events.

Descriptor records are the fundamental structures from which Apple events

are constructed. A descriptor record is a data structure of type AEDesc; it

consists of a handle to data and a descriptor type that identifies the type of the

data referred to by the handle.

The data referred to by the dataHandle field in the descriptor record is private

to the Apple Event Manager. You can supply or extract this data only by

The following figure illustrates a descriptor record with a descriptor type of

typeType, which specifies that the data in the descriptor record must consist

of a four-character code. The data in this particular descriptor record is

specified by the constant kCoreEventClass, whose value is 'aevt'.

A descriptor record with event class data

A descriptor record that contains the address of the target or source of an

Apple event is called an address descriptor record

As you will see later, the address can be specified as an application signature,

a process serial number, a session ID, a target ID record, or a data type that

you define.

Data for attributes and parameters is contained in descriptor records. The

attributes and parameters themselves are identified by keywords. The

AEKeyword data type is defined as a four-character code.

Constants are typically used for keywords. For a list of these keyword

constants, their four-character codes, and the attributes and parameters they

A data structure of type AEKeyDesc consists of a keyword and a descriptor

record. This data structure, called a keyword-specified descriptor record, is

used by the Apple Event Manager to fully identify and describe an attribute

or a parameter of an Apple event.

The following figure illustrates a keyword-specified descriptor record for

the event class attribute of an Open Documents event. The keyEventClassAttr

keyword identifies its descriptor record as containing event class data. The data

is of the typeType descriptor type, and the data identifies the event class as

kCoreEventClass.

A keyword-specified descriptor record for the event class attribute of an

Open Documents event.

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