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Chapter 17: Trigger Control

Events

181

Psion Mobile Devices Developers Guide

between the trigger presses if a double-click event is to be generated. The default double-click time is

0(zero).

A double-click event is generated when both the following are true:

• A trigger source is pressed and released within ½ the configured double-click time, and

• The trigger source is pressed a second time before the double-click time expires.

Each trigger source has its own double-click time.

The trigger that is associated with the internal scanner uses the double-click time configured for the

scanner either through the GUI or through the SDK scanner namespace. See Section Double-click settings

on page 102 for more information.

17.7 Events

To receive trigger events, a trigger consumer must be associated with a trigger source and registered to

receive trigger events. A trigger consumer can receive events from several triggers. Each event contains

the identity of the trigger source that originated it. To receive trigger events an application must complete

the following steps:

1. Register as a trigger consumer.

2. Register the trigger consumer to receive trigger events.

3. Associate the trigger consumer with a trigger source ID.

A trigger consumer can deregister as a trigger consumer to stop receiving all events. It can remove the

association with one, or all, trigger source IDs to stop receiving events from one, or all, trigger sources.

A trigger event is generated when the state of a trigger source changes on a Psion computer. There are two

trigger states:

• Trigger-down.

• Trigger-up.

Trigger-down event: This event is generated when the pistol grip trigger or the button associated with a

trigger source is pressed.

Trigger-up event: This event is generated when the trigger or button associated with a trigger source

is released.

Any trigger event can have one of the following flags set:

• Single-click flag.

• Double-click flag.

Single-click flag: This flag is set when a trigger source is pressed and released within ½ the double-click

time configured for that trigger source. The double-click time must be greater than 0 (zero).

Double-click flag: This flag is set when a trigger source is pressed twice within the double-click time config-

ured for that trigger source. The double-click time must be greater than 0 (zero).

17.7.1 Simulated Events

The Mobile Devices SDK can generate a simulated trigger event. This is forwarded to the trigger driver. The

trigger driver sends the event to all registered trigger consumers which also have a trigger association with

the specified trigger event source.

This method generates both trigger-up and trigger-down events.

Any application that simulates trigger events using this method must be well behaved. A trigger-down

event must always be followed by a trigger-up event. Sending out multiple trigger-down and trigger-up

events in a row can result in unexpected behaviour. An application must not remove a trigger association

after a trigger-down event—the associated trigger-up event must be simulated before the association

is ended.

17.7.2 Single-Click Events and Double-Click Events

Single-click events and double-click events can be generated by any trigger source, if the configured

double-click time for the trigger source is not 0 (zero).

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