Class Filter

Provides a generic view of a sequence of bytes.

A Filter is the abstract base class of all filters. A filter is an abstraction of a sequence of bytes, such as a file, an input/output device, an inter-process communication pipe, or a TCP/IP socket. The Filter class and its derived classes provide a generic view of these different types of input and output, isolating the programmer from the specific details of the operating system and the underlying devices.

Besides providing access to input/output sources Filters can be also to transform the data (e.g. to compress the data stream, to normalize the image data, to encrypt data, etc). Filters can also be attached to each other to form pipelines. For example, a filter used to open an image data file can be attached to a filter that decompresses the data, which is attached to another filter that will normalize the image data.

Depending on the underlying data source or repository, filters might support only some of these capabilities. An application can query a stream for its capabilities by using the IsInputFilter() and CanSeek() properties.

To read or write data to a filter, a user will typically use FilterReader/FilterWriter class. instead of using Filter methods

MappedFile file = new MappedFile("my_stream.txt");
FilterReader reader = new FilterReader(file);
while (reader.read(...)) ...

Inheritance

Filter

Implements

IDisposable

Inherited Members

object.ToString()

object.Equals(object)

object.Equals(object, object)

object.ReferenceEquals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

Namespace: pdftron.Filters

Assembly: PDFNet.dll

Syntax

public class Filter : IDisposable

Methods

AttachFilter(Filter)

Attaches a filter to the this filter. If this filter owns another filter it will be deleted. This filter then becomes the owner of the attached filter.

Declaration

public virtual void AttachFilter(Filter attach_filter)

Parameters

Type	Name	Description
Filter	attach_filter	the attach_filter

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

Begin()

Get the begin of the buffer

Declaration

public virtual ref byte Begin()

Returns

Type	Description
byte	beginning of the buffer of `Size()` bytes that can be used to read or write data.

CanSeek()

Check whether the stream supports seeking.

Declaration

public virtual bool CanSeek()

Returns

Type	Description
bool	true if the stream supports seeking; otherwise, false. default is to return false.

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

Consume(int)

Moves the Begin() pointer num_bytes forward.

Declaration

public virtual void Consume(int num_bytes)

Parameters

Type	Name	Description
int	num_bytes	number of bytes to consume. num_bytes must be less than or equal to `Size()`.

Count()

Get the number of bytes consumed since opening the filter or the last Seek operation

Declaration

public virtual int Count()

Returns

Type	Description
int	the number of bytes consumed since opening the filter or the last Seek operation

CreateInputIterator()

Create Filter iterator. Filter iterator similar to a regular filter. However, there can be only one owner of the attached filter.

Declaration

public virtual Filter CreateInputIterator()

Returns

Type	Description
Filter	the filter

Remarks

Derived classes should make sure that there is only one owner of the attached stream. Otherwise the attached stream may be deleted several times.

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

Dispose()

Releases all resources used by the Filter

Declaration

public override sealed void Dispose()

Dispose(bool)

Declaration

[HandleProcessCorruptedStateExceptions]
protected virtual void Dispose(bool A_0)

Parameters

Type	Name	Description
bool	A_0

~Filter()

Allows a Filter to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.

Declaration

protected ~Filter()

Flush()

Forces any data remaining in the buffer to be written to input or output filter.

Declaration

public virtual void Flush()

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

FlushAll()

Forces any data remaining in the filter chain to the source or destination.

Declaration

public virtual void FlushAll()

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

GetAttachedFilter()

Get the attached filter.

Declaration

public virtual Filter GetAttachedFilter()

Returns

Type	Description
Filter	attached Filter or a NULL filter if no filter is attached.

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

GetDecodeName()

Gets the decode name.

Declaration

public virtual string GetDecodeName()

Returns

Type	Description
string	string representing the name of corresponding decode filter as it should appear in document (e.g. both ASCIIHexDecode and ASCIIHexEncode should return ASCIIHexDecode).

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

GetFilePath()

Gets the file path.

Declaration

public virtual string GetFilePath()

Returns

Type	Description
string	the file path to the underlying file stream. Default implementation returns empty string.

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

GetName()

Gets the name.

Declaration

public virtual string GetName()

Returns

Type	Description
string	descriptive name of the filter.

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

GetSourceFilter()

Get the source filter.

Declaration

public virtual Filter GetSourceFilter()

Returns

Type	Description
Filter	the first filter in the chain (usually a file filter)

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

IsInputFilter()

Checks if is input filter.

Declaration

public virtual bool IsInputFilter()

Returns

Type	Description
bool	boolean indicating whether this is an input filter.

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

ReleaseAttachedFilter()

Release the ownership of the attached filter. After the attached filter is released this filter points to NULL filter.

Declaration

public virtual Filter ReleaseAttachedFilter()

Returns

Type	Description
Filter	Previously attached filter.

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

Seek(int, ReferencePos)

When overridden in a derived class, sets the position within the current stream.

Declaration

public virtual void Seek(int offset, Filter.ReferencePos origin)

Parameters

Type	Name	Description
int	offset	A byte offset relative to origin. If offset is negative, the new position will precede the position specified by origin by the number of bytes specified by offset. If offset is zero, the new position will be the position specified by origin. If offset is positive, the new position will follow the position specified by origin by the number of bytes specified by offset.
Filter.ReferencePos	origin	A value of type ReferencePos indicating the reference point used to obtain the new position

Remarks

After each Seek() operation the number of consumed bytes (i.e. Count()) is set to 0.

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

SetCount(int)

Sets a new counting point for the current filter. All subsequent Consume() operations will increment this counter. Make sure that the output filter is flushed before using SetCount().

Declaration

public virtual int SetCount(int new_count)

Parameters

Type	Name	Description
int	new_count	new counting point

Returns

Type	Description
int	the value of previous counter

SetStreamLength(int)

The functions specifies the length of the data stream. The default implementation does not do anything. For some derived filters such as file segment filter it may be useful to override this function in order to limit the stream.

Declaration

public virtual void SetStreamLength(int bytes)

Parameters

Type	Name	Description
int	bytes	the new stream length

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

Size()

Get size of buffer

Declaration

public virtual int Size()

Returns

Type	Description
int	the size of buffer returned by `Begin()`. If the `Size()` returns 0 end of data has been reached.

Tell()

Reports the current read position in the stream relative to the stream origin.

Declaration

public virtual int Tell()

Returns

Type	Description
int	The current position in the stream

Exceptions

Type	Condition
PDFNetException	PDFNetException the PDFNet exception

WriteToFile(string, bool)

Writes the entire filter, starting at current position, to specified filepath. Should only be called on an input filter.

Declaration

public void WriteToFile(string path, bool append)

Parameters

Type	Name	Description
string	path	The output filepath.
bool	append	'Frue' to append to existing file contents, 'False' to overwrite.

Implements

IDisposable