Commands +and Responses

This tutorial deals with the commands and responses available for remote +control framework applications.

Intended Audience:

This tutorial is designed for Symbian licensees and 3rd party application +developers.

Using Commands and Responses

The following tasks +will be covered in this tutorial:

As Controller
- Send Commands
- Receive responses
As Target
- Receive Commands
- Send Responses

Controller

The device used to send control commands +to a remote target is the controller. There are two broad kinds of controller +operations that need to be understood: sending commands and receiving responses. +They are discussed below.

Sending Commands

Commands +are sent to a remote control target device to tell the device to do something. +This may include changing the volume setting, requesting a track listing, +starting or stopping music playback, requesting a file listing, or depending +on the kind of device being controlled, telling the device to move in some +way.

... + CRemConCoreApiController* iCoreController; +... // open the controller as previously discussed. + TRequestStatus stat; + TUint numRemotes; + // numRemotes is a value representing a specific participating device. + iCoreController->Play(stat, numRemotes, ERemConCoreApiButtonClick); + User::WaitForRequest(stat); + LEAVEIFERRORL(stat.Int());

When a target receives the command +it will handle it in an appropriate way, as discussed in the next section. +The target may also send a response to the controller.

Receiving +Responses

If a target sends a response to a received command the +controller needs to handle the response. The response could be something as +simple as an acknowledgement that a command has been received or it could +be as complex as a listing of audio tracks that the controller needs to process +in some way.

To receive responses the application should implement +the MRemConCoreApiControllerObserver controller observer +interface. It then receives callbacks when a response has arrived.

void MrccacoResponse(TRemConCoreApiOperationId aOperationId, + TInt aError); +... +void CRemConTestOuter::MrccacoResponse(TRemConCoreApiOperationId aOperationId, + TInt aError) + { + switch ( aOperationId ) + { + case ERemConCoreApiPlay: + iManager.MtmWrite(_L8("\ta 'play' response came in with error %d"), aError); + break; + case ERemConCoreApiStop: + iManager.MtmWrite(_L8("\ta 'stop' response came in with error %d"), aError); + break; + case ERemConCoreApiVolumeUp: + iManager.MtmWrite(_L8("\ta 'VolumeUp' response came in with error %d"), aError); + break; + case ERemConCoreApiVolumeDown: + iManager.MtmWrite(_L8("\ta 'VolumeDown' response came in with error %d"), aError); + break; + case ERemConCoreApiForward: + iManager.MtmWrite(_L8("\ta 'Forward' response came in with error %d"), aError); + break; + case ERemConCoreApiBackward: + iManager.MtmWrite(_L8("\ta 'Backward' response came in with error %d"), aError); + break; + } + }

Responses are often followed up by the controller with +a series of actions such as presenting the information provided by the response +to the user, waiting for the user to make a choice of some kind, and sending +a new command, which begins the whole process again.

Target

A target device is set up to wait for and +handle commands sent to it from a controller and respond in some way to those +commands.

Receiving Commands

To receive a command, +such as a request to increase the volume or return a listing of audio tracks, +the client must implement the MRemConCoreApiTargetObserver target +observer interface. It then will receive a callback through this interface +when a command is received.

iCoreTarget = CRemConCoreApiTarget::NewL(*iInterfaceSelector, *this); +... +void CRemConTestOuter::MrccatoPlay(TRemConCoreApiPlaybackSpeed aSpeed, + TRemConCoreApiButtonAction aButtonAct) + { + ... + // used below + TRequestStatus stat; + // send the response + iCoreTarget->PlayResponse(stat, KErrNone); + User::WaitForRequest(stat); + ... + }

Sending Responses

Once the command has +been handled the target will send a response to the controller. The response +could be a simple acknowledgement, an error message, or a listing of files +or music tracks or some other data. Use the CRemConCoreApiTarget interface.

... +CRemConCoreApiTarget* iCoreTarget; +... + { + ... + // from above + TRequestStatus stat; + // send the response + iCoreTarget->PlayResponse(stat, KErrNone); + User::WaitForRequest(stat); + ... + }

What's next?

Remote +Control Basics
Starting +as Controller
Starting +as Target
Commands and Responses - +This document