DJI Waypoint mission listeners

Question

I need to create/upload/start waypoint mission on one button. When user press button drone should move up for certain number of point based on current position. User can stop mission and again start new one. My logic here is next:

1. I initialize mission with points
2. Load mission
3. Add Listeners to mission operator
4. Upload mission
5. Mission starts on listener

missionOperator.addListener(toUploadEvent: self, with: DispatchQueue.main) { (event) in
    if event.currentState == .readyToExecute {
        self.startMission()
    }
}

I'm reading documentation for days and trying to understand how this thing work, but I'm missing something obviously. Listeners are created on waypoint mission operator, but if I create listeners before loading mission they are not called. If I create listeners every time I load mission, startMission() is called multiple times (first time is called ones, but after one mission is stopped or finished, next time startMission() gets called two times)

So, I guess that my questions would be: What is right moment to add listeners and to remove them since I'm calling startMission() from listeners? Actually what is appropriate way to init/upload/start mission on one button, and be able to do that multiple times?

Answer 1

You need to remove the upload listener when the the upload succeeded and the event state is readyToExecute. Also when the event contains an error, or the state is readytoupload/notsupported/disconnected. Pretty much in every case except when it's still in the state 'uploading'.

When you start the mission, add a listener for execution events, and one for finished. Remove those again when the mission is stopped/cancelled, has an error, or finishes successfully.

Even though you use Swift, I suggest looking at the more complete Objective C sample code, which includes examples of several different types of missions.