/**
* <summary>
* Registers the callback function that is invoked on every change of advertised value.
* <para>
* The callback is invoked only during the execution of <c>ySleep</c> or <c>yHandleEvents</c>.
* This provides control over the time when the callback is triggered. For good responsiveness, remember to call
* one of these two functions periodically. To unregister a callback, pass a null pointer as argument.
* </para>
* <para>
* </para>
* </summary>
* <param name="callback">
* the callback function to call, or a null pointer. The callback function should take two
* arguments: the function object of which the value has changed, and the character string describing
* the new advertised value.
* @noreturn
* </param>
*/
public async Task <int> registerValueCallback(ValueCallback callback)
{
string val;
if (callback != null)
{
await YFunction._UpdateValueCallbackList(this, true);
}
else
{
await YFunction._UpdateValueCallbackList(this, false);
}
_valueCallbackTemperature = callback;
// Immediately invoke value callback with current value
if (callback != null && await this.isOnline())
{
val = _advertisedValue;
if (!(val == ""))
{
await this._invokeValueCallback(val);
}
}
return(0);
}