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Disposing of Apple Event Data Structures

If you create a descriptor, you must dispose of it when you are finished with it to prevent memory leaks. For example, when you extract a descriptor using the AEGetParamDesc, AEGetAttributeDesc, AEGetNthDesc, or AEGetKeyDesc function, you get a copy of the descriptor. You call the AEDisposeDesc function to dispose of your copy, thereby deallocating the memory used by its data.

Listing 4-6 shows how to dispose of a descriptor list returned by AEGetParamDesc.

Listing 4-6  Disposing of a descriptor list obtained from the direct object of an Apple event

AEDescList  docList;

OSErr       err;

err = AEGetParamDesc(theAppleEvent, keyDirectObject, typeAEList, &docList);

// Check for error, then perform operations on the descriptor list here.

AEDisposeDesc(&docList);

You can safely call AEDisposeDesc on a null descriptor (but not on a null pointer!) A null descriptor is one that has been initialized as shown in the following code snippet.

AEDesc      someDesc = { typeNull, 0L };

// Code to obtain a descriptor, which may fail.

// Safe to dispose, whether or not previous code succeeded.

AEDisposeDesc(&someDesc);

You can perform the same initialization using the AEInitializeDesc function, as shown in this code snippet.

    AEDesc      someDesc;

    AEInitializeDesc(&someDesc);

When you obtain a copy of a descriptor with one of the buffer-based functions, such as AEGetAttributePtr or AEGetNthPtr, the data is copied into a buffer provided by your application. You must then free any allocated memory when finished with the buffer.

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