previousState of a String item

Setup, Configuration and Use Beginners
1

I have troubles with the previousState for a String Item.
what is the correct syntax to check the previousState?
I`ve setup RRJ4D and MapDB as persistences…
CallState.previousState.state == “IDLE”

var Number Volumememory = 0

rule "Call State Trigger"

when
Item CallState changed
then
if (CallState.state == "IDLE") {
    if (Matthias_Handy.state == ON) {
    logInfo("CallState", "IDLE")// No call activity
    SqueezeboxVolume1.sendCommand(Volumememory)
    }
} 
else if (CallState.state == "RINGING") {
    if (Matthias_Handy.state == ON) {
        Volumememory = SqueezeboxVolume1.state as Number
        SqueezeboxVolume1.sendCommand(30)
            //Player_Office.sendCommand(PAUSE)
        logInfo("CallState", "Ringing")// A new call arrived and is ringing or waiting. In the latter case, another call is already active.
    }  
} 
else if (CallState.state == "OFFHOOK" && CallState.previousState.state == "IDLE") {
    if (Matthias_Handy.state == ON) {
        SqueezeboxVolume1.sendCommand(30)
        Volumememory = SqueezeboxVolume1.state as Number
        //Player_Office.sendCommand(PAUSE)
        logInfo("CallState", "Offhook")// At least one call exists that is dialing, active, or on hold, and no calls are ringing or waiting.
    }    
}
end
2

PreviousState is am implicit variable available in a rule with a changed trigger, hence no persistence is needed .
The correct syntax is posted Here

3

already tried .previousState().state

rule " test"  
            when    
                    Item VSwitch1 changed 
            then    
                    logInfo("testrule", "Callstate: "+CallState.previousState().state  
            end

output is “0.0”
2019-12-11 10:36:31.065 [INFO ] [ipse.smarthome.model.script.testrule] - Callstate: 0.0
but the Callstate is either “IDLE”, “OFFHOOK” or “RINGING”…

4

Just use previousState on its own:

else if (CallState.state == "OFFHOOK" && previousState == "IDLE") {

The use of implicit variables is documented here: https://www.openhab.org/docs/configuration/rules-dsl.html#implicit-variables-inside-the-execution-block

5

There are two completely different things called previousState.

One is an implicit variable , that exists in any rules with a changed trigger. It’s derived from the changed event, not from the Item, not from persistence.

logInfo(“test”, "implicit " + previousState)

The other is a method of an Item to access persistence. Obviously any results there depend on if/how your Item is persisted and your service defaults.

logInfo(“test”, "persistence fetch " + myItem.previousState().state)