Fires before a registry value's information is retrieved.
The 'callback' is called when the 'BeforeQueryValue' event is emited.
The argument 'e' has the following properties:
e.keyContext e.valueName e.requestedFields e.valueType e.integerValue e.stringValue e.binaryValue e.maxBinaryValueSize e.binaryValueSize e.processed e.fireAfterEvent e.stopFiltering e.resultCode
This event fires before a registry value's information is retrieved.
The KeyContext parameter is a placeholder for application-defined data associated with the registry key. Please refer to the Contexts topic for more information. Note that this event does not expose the registry key's name for performance reasons; applications that need it should store it in KeyContext during the BeforeCreateKey/BeforeOpenKey event so that it can be retrieved when this event fires.
The ValueName parameter reflects the name of the registry value.
The RequestedFields parameter indicates which pieces of information about the registry value were requested. The value of this parameter is a combination of one or more of the following:
|REG_VALUEFIELD_TYPE||1||A registry value's type.|
|REG_VALUEFIELD_NAME||2||A registry value's name.|
|REG_VALUEFIELD_DATA||4||A registry value's data.|
The ValueType parameter specifies the registry value's type, and determines which of the other parameters holds the registry value's data (please refer to their descriptions for more information). Possible values are:
|REG_VALUETYPE_SZ||1||A unicode string.|
|REG_VALUETYPE_EXPAND_SZ||2||A unicode string that contains environmental variable references.|
|REG_VALUETYPE_DWORD||4||A 32-bit number.|
|REG_VALUETYPE_MULTI_SZ||7||Multiple unicode strings.|
|REG_VALUETYPE_QWORD||11||A 64-bit number.|
For REG_VALUETYPE_MULTI_SZ, the data is formatted as multiple individual ETB-terminated strings concatenated together into a single null-terminated string (where ETB is the End-of-Transmission-Block character; 23/0x17). For example, the strings This is, a multistring, value. would be encoded as This is[ETB]a multistring[ETB]value.[ETB][NUL].
Note that, as Microsoft's Registry Value Types article describes, the native multistring data format uses null-terminators for the individual strings (e.g., This is[NUL]a multistring[NUL]value.[NUL][NUL]); CBRegistry converts the individual null terminators to/from ETB characters internally for applications' convenience.
The BinaryValue parameter points to a memory buffer that holds the registry value's data if ValueType is REG_VALUETYPE_BINARY. The MaxBinaryValueSize and BinaryValueSize parameter specify the capacity of the BinaryValue buffer and the length of the data it contains (respectively), in bytes.
Always check MaxBinaryValueSize before copying any data into the BinaryValue buffer. If the buffer is large enough to hold all of the data, copy the data into it, and then update BinaryValueSize accordingly. If the buffer is not large enough, do not copy any data into it; instead, set BinaryValueSize to the required buffer size (i.e., the size of the data), and return the ERROR_MORE_DATA (234) error code via ResultCode.
The Processed parameter indicates whether the underlying request has been handled successfully. Applications should set this parameter to true if they've handled the request themselves (this will prevent the corresponding After* event from being called). Note that this parameter's value is ignored if an error is returned via ResultCode.
The FireAfterEvent parameter specifies whether the corresponding After* event should be fired; it is true by default. Note that, regardless of how this parameter is set, the corresponding After* event will not fire if Processed is true, or if an error code is returned via ResultCode.
The StopFiltering parameter specifies whether the class's system driver should ignore all further operations for the registry key; it is false by default. Applications may set this parameter to true to prevent any further events from firing for the registry key.
The ResultCode parameter will always be 0 when the event is fired. If the event cannot be handled in a "successful" manner for some reason (e.g., a resource isn't available, security checks failed, etc.), set it to a non-zero value to report an appropriate error. Please refer to the Error Reporting and Handling topic for more information.
This event is fired synchronously; please refer to the Event Types topic for more information.