Tactile feedback client API

The Tactile feedback client API is used for producing tactile feedback for different touch events.

The Tactile feedback client API is a library API that has been implemented with a client-server technique. A major part of the processing is done on the client side, and thus API calls don't necessarily generate a client-server transaction immediately. Instead for e.g. changes to area registry are buffered, and then transferred to server-side at once.

You can use tactile feedback in, for example, the following cases:

When the user starts to scroll with the scroll bar, user can feel and/or hear when the scroll bar thumb has been caught.
When button is pressed, user can feel and/or hear the button being pressed.

The concept of logical feedback type is very important from this API's point of view.

In practice it means that, for example, you should not try to use this API for producing vibrator feedback only. Instead, logical feedback types such as "basic" or "sensitive" are used on this level, and the actual physical effect then depends on the settings and device configuration. This way the feedback works in a unified way from the end user point of view in the whole device.

For user experience guidelines on tactile feedback, see Tactile feedback.

For information on using the API, see Providing tactile feedback for touch events.

For the Tactile feedback client API classes and header files, see Classes and Definitions.

API class structure

All functionality of the Tactile feedback client API is provided in the class MTouchFeedback.

Constraints

This API is valid for all platforms running on Symbian OS 9.4 or later.

Error handling

The leave mechanism of Symbian OS environment is used to handle memory exhaustion. The panic mechanism is not used.

The table below presents possible error conditions and responses to them.

**Table:** Possible error situations when using Tactile Feedback Client API
Error situation	Response
`SetFeedbackArea` returns `KErrNoMemory` in case of an OOM situation.	This error can usually be ignored by the application.
`SetFeedbackArea` returns `KErrArgument`	The given `CCoeControl` pointer is a `NULL` pointer or the control does not have any window associated with it (i.e., the feedback area setting is attempted before `SetContainerWindow` has been called on the control).
`SetFeedbackArea` returns `KErrNotSupported`.	The given logical feedback type or triggering event type is out of range.
A tactile feedback enabled control is moved with `CCoeControl::SetPosition`, but the feedback area is not moved.	The control must override the `CCoeControl::PositionChanged` function, and update the feedback area there the same way as in the `SizeChanged` function.
Area registry updates not are effective fast enough. This might happen in some applications which use very many frequently running active objects, so that the `CIdle` object used by the implementation of this API gets no change to run.	Use the `FlushRegistryUpdates` function for forcing an update to the server side after doing all updates on the client side.
A control's feedback areas are not automatically disabled when the control is dimmed.	`CCoeControl::SetMopParent` has not been called on the control, and thus the object provider hierarchy is broken.

Memory overhead

Using direct feedback does not cause additional memory overhead.

Area registry based feedback consumes approximately 32 bytes for each feedback area.

Extensions to the API

New logical feedback types can be added in later releases. Otherwise the Tactile feedback client API does not explicitly support any kinds of extensions to it.