All Databases Inside Mac - AppleEvents

Getting Data Out of an Attribute

You can use the AEGetAttributePtr or AEGetAttributeDesc function to

get the data out of the attributes of an Apple event.

You can get the data out of an attribute using the AEGetAttributePtr

function. You specify the Apple event that contains the desired attribute, the

keyword of the desired attribute, the descriptor type the function should use to

return the data, a buffer to store the data, and the size of this buffer as

parameters to the AEGetAttributePtr function. The AEGetAttributePtr

function returns the descriptor type of the returned data and the actual size of

the data, and it places the requested data in the specified buffer.

For example, this code gets the data out of the keyEventSourceAttr attribute of

an Apple event:

AppleEvent theAppleEvent;

DescType returnedType;

short sourceOfAE;

Size actualSize;

OSErr myErr;

myErr = AEGetAttributePtr(& theAppleEvent, keyEventSourceAttr,

typeShortInteger, & returnedType, (Ptr) &sourceOfAE,

sizeof(sourceOfAE), & actualSize);

The keyEventSourceAttr keyword specifies the attribute to get the data from.

The typeShortInteger descriptor type specifies that the data should be returned

as a short integer; the returnedType variable contains the actual

descriptor type that is returned. You also must specify a buffer to hold the

returned data and specify the size of this buffer. The AEGetAttributePtr

function returns the actual size of the data returned in the actualSize variable.

You can check this value to make sure you got all the data.

As with the AEGetParamPtr function, you can request that

AEGetAttributePtr return the data using the descriptor type of the original

data, or you can request that the Apple Event Manager coerce the data into a

descriptor type that is different from the original.

In this example, the AEGetAttributePtr function returns the requested data

in the sourceOfAE variable, and you can determine the source of the Apple

event by examining this value.

The next example shows how to use the AEGetAttributePtr function to get

data out of the keyMissedKeywordAttr attribute. After your handler extracts

all known parameters from an Apple event, it should check whether the

keyMissedKeywordAttr attribute exists. If it does, then your handler did not

get all of the required parameters.

Note that if AEGetAttributePtr returns the errAEDescNotFound result

code, then the keyMissedKeywordAttribute does not exist-which indicates that

your application has extracted all of the required parameters. If

AEGetAttributePtr returns noErr, then the keyMissedKeywordAttribute

does exist-which indicates that your handler did not get all of the required

parameters.

myErr = AEGetAttributePtr(& theAppleEvent, keyMissedKeywordAttr,

typeWildCard, & returnedType, nil, 0,

& actualSize);

The data in the keyMissedKeywordAttr attribute contains the first required

parameter, if any, that your handler didn't retrieve. If you want this data

returned, specify a buffer to hold the data and specify the size of the buffer.

Otherwise, as in this example, specify NIL as the buffer and 0 as the size of the

buffer.

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