State Changes Initiated by GAPI
When the coordinator writes a new value to an attribute on another device, the device will confirm that it received the write request. This should trigger an update listener in GAPI.
State Changes Initiated Outside of GAPI
In many cases, the state change will be initiated by user interaction or environmental changes affecting the other devices on the network. For example: as the temperature in a room changes, the value of the LocalTemperature attribute for a thermostat in that room will change. In cases like this, Attribute Reporting may be used to keep the gateway in sync with attribute values for other devices.
The Zigbee specifications dictate that some attributes are "reportable", meaning that it will be possible to prompt notifications to be sent to other devices when the attribute value changes. You simply need to enable attribute reporting using the Binding and Attribute Reporting API.
Once an attribute has been configured for reporting, a handler will be triggered in GAPI when it changes.