Object types for storages and streams
PowerBuilder has two object types that are the equivalent
of the storages and streams stored in OLE files. They are:
-
OLEStorage
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OLEStream
These objects are class user objects, like a Transaction or
Message object. You declare a variable, instantiate it, and open
the storage. When you are through with the storage, you close it
and destroy the variable, releasing the OLE server and the memory
allocated for the variable.
Opening a storage associates an OLEStorage variable with a
file on disk, which can be a temporary file for the current session
or an existing file that already contains an OLE object. If the
file does not exist, PowerBuilder creates it.
You can put OLE objects in a storage with the SaveAs function.
You can establish a connection between an OLE control in a window
and a storage by calling the Open function for
the OLE control.
A stream is not an OLE object and cannot be opened in a control.
However, streams allow you to put your own information in a storage
file. You can open a stream within a storage or substorage and read
and write data to the stream, just as you might to a file.
Performance tip
Storages provide an efficient means of displaying OLE data.
When you insert a file created by a server application into a control,
OLE has to start the server application to display the object. When
you open an object in an OLE storage, there is no overhead for starting
the server—OLE uses the stored presentation information
to display the object. There is no need to start the server if the
user never activates the object.