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# 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

object
Filter
ASCII85Encode
FlateEncode
MappedFile
MemoryFilter
StreamAdapterFilter
Image2RGB

##### 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