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Declaration
property IOHandler: TIdIOHandler;
Summary
The input / output mechanism for the connection.
Description
IOHandler is a TIdIOHandler property that represents the input / output mechanism used for connecting, disconnecting, sending, and receiving on the connection.
TIdIOHandler, and descendant classes, provide an abstraction that allows use of Socket connections, streams, or any input / output data source where an IOHandler has been written to the interface for the framework.

IOHandler is used in methods that perform low-level operations for the connection such as connecting, disconnecting, sending, and receiving. The properties, methods, and events in the IOHandler generally belong to the following usage categories:


Configuration
Destination
Host
MaxCapturedLines
MaxLineLength
Port
ReadTimeout
RecvBufferSize
SendBufferSize


Connection State
CheckForDataOnSource
CheckForDisconnect
Close
CloseGracefully
ClosedGracefully
Connected
Open
Opened
ReadLnTimedout
Readable


Buffers and Buffering
InputBuffer
InputBufferAsString
InputBufferIsEmpty
InputBufferToStream
WriteBufferCancel
WriteBufferClear
WriteBufferClose
WriteBufferFlush
WriteBufferOpen
WriteBufferThreshhold
WriteBufferingActive


Read Operations
AllData
Capture
InputLn
ReadBytes
ReadCardinal
ReadChar
ReadInt64
ReadInteger
ReadLn
ReadLnSplit
ReadLnWait
ReadSmallInt
ReadStream
ReadString
ReadStrings
WaitFor


Write Operations
Write
WriteDirect
WriteLn
WriteFile


Connection Events
OnWork
OnWorkBegin
OnWorkEnd
MaxLineAction
Intercept

When accessing IOHandler in application code, always cast the IOHandler to the correct descendant class. This allows access to any methods or properties in the descendant that cannot be represented in the ancestor class at runtime.

Use Socket to access an IOHandler known to descend from the TIdIOHandlerSocket class and allow access to the socket handle and socket options for the binding.

IOHandler can be assigned using CreateIOHandler and the class reference needed for creating the new IOHandler instance. Use GIOHandlerClassDefault to access a class reference for creating the default IOHandler in Indy.

An existing TIdIOHandler instance may also be assigned directly to the IOHandler property. When an object instance is assigned to the IOHandler property, the event handler properties in OnWorkBegin, OnWork, and OnWorkEnd are set to the internal event handler methods for the connection object. These event handlers may be re-assigned later in the users application.

If the new IOHandler is derived from TIdIOHandlerSocket, the value in Socket is updated to reflect the IOHandler instance. In other words, both IOHandler and Socket may contain references to the new IOHandler.

IOHandler is freed in Destroy when the ManagedIOHandler property contains True, or during the opRemove notification message for the component.

See Also
TIdIOHandler, TIdIOHandlerSocket, TIdIOHandlerStream, CreateIOHandler, ManagedIOHandler, Destroy, Connected, Disconnect, SendCmd, WriteHeader, WriteRFCStrings
Class
TIdTCPConnection