log4net SDK Reference |

# IFilter Interface

Implement this interface to provide customized logging event filtering

For a list of all members of this type, see IFilter Members.

[Visual Basic]
Public Interface IFilter
Implements IOptionHandler
[C#]
public interface IFilter : IOptionHandler

#### Types that implement IFilter

Type | Description
--- | ---
DenyAllFilter | This filter drops all LoggingEvent.
FilterSkeleton | Subclass this type to implement customized logging event filtering
LevelMatchFilter | This is a very simple filter based on Level matching.
LevelRangeFilter | This is a simple filter based on Level matching.
LoggerMatchFilter | Simple filter to match a string in the event's logger name.
MdcFilter | Simple filter to match a keyed string in the MDC
NdcFilter | Simple filter to match a string in the NDC
PropertyFilter | Simple filter to match a string an event property
StringMatchFilter | Simple filter to match a string in the rendered message

#### Remarks

Users should implement this interface to implement customized logging event filtering. Note that Logger and AppenderSkeleton, the parent class of all standard appenders, have built-in filtering rules. It is suggested that you first use and understand the built-in rules before rushing to write your own custom filters.

This abstract class assumes and also imposes that filters be organized in a linear chain. The Decide method of each filter is called sequentially, in the order of their addition to the chain.

The Decide method must return one of the integer constants Deny, Neutral or Accept.

If the value Deny is returned, then the log event is dropped immediately without consulting with the remaining filters.

If the value Neutral is returned, then the next filter in the chain is consulted. If there are no more filters in the chain, then the log event is logged. Thus, in the presence of no filters, the default behavior is to log all logging events.

If the value Accept is returned, then the log event is logged without consulting the remaining filters.

The philosophy of log4net filters is largely inspired from the Linux ipchains.

#### Requirements

Namespace: log4net.Filter

Assembly: log4net (in log4net.dll)

#### See Also

IFilter Members | log4net.Filter Namespace