[Overview][Types][Classes][Index] Reference for unit 'resdatastream' (#fcl-res)

TResourceDataStream

[Properties (by Name)] [Methods (by Name)] [Events (by Name)]

Stream class that provides copy-on-write functionality

Declaration

Source position: resdatastream.pp line 61

type TResourceDataStream = class(TStream)

protected

  function GetPosition; override;

  procedure SetPosition(); override;

  function GetSize; override;

  procedure SetSize64(); override;

public

  constructor Create();

  

Creates a new object

  destructor Destroy; override;

  function Compare();

  

Compares the stream to another one

  procedure SetCustomStream();

  

Sets a custom stream as the underlying stream

  function Read(); override;

  function Write(); override;

  function Seek(); override;

  property Cached: Boolean; [rw]

  

Controls the copy-on-write behaviour of the stream

end;

Inheritance

TResourceDataStream

  

Stream class that provides copy-on-write functionality

|

TStream

|

TObject

Description

This class provides the copy-on-write mechanism of TAbstractResource.RawData, via more levels of indirection.

It uses an underlying stream, to which it redirects operations.

The underlying stream can be a TCachedDataStream descendant, a memory stream or a custom stream. Usually when a resource is loaded from a stream, the underlying stream is a TCachedDataStream descendant, which provides a read-only stream-like interface over a portion of the original stream (that is, the part of the original stream where resource data resides). When TResourceDataStream is requested to write data, it replaces the underlying stream with a memory stream, whose contents are copied from the previous underlying stream: this way, copy-on-write functionality can be achieved.

As said before, third possibility is to have a custom stream as the underlying stream: a user can set this stream via TAbstractResource.SetCustomRawDataStream method, which in turn calls TResourceDataStream.SetCustomStream

Figure: Levels of indirection

.
                     TResourceDataStream
                              |
       _______________________|_______________________________
      |                       |                               |
TMemoryStream     TCachedDataStream descendant          custom stream
                         /           \
 _______________________|_____________|______________________________
|                o r i g|i n a l   s t|r e a m                       |
|_______________________|_____________|______________________________|

See also

TCachedDataStream

  

Base cached stream class

TResourceDataStream.Create

  

Creates a new object

TResourceDataStream.SetCustomStream

  

Sets a custom stream as the underlying stream


Documentation generated on: May 14 2021