Does not work in flutter project

[matthias-glatthorn]

I try to use JPSVolumeButtonHandler in a flutter project, but the volume buttons are not detected. This is how I used it:

AppDelegate.swift:

var volumeButtonHandler: JPSVolumeButtonHandler?
volumeButtonHandler = JPSVolumeButtonHandler(up: {self.doSomething()}, downBlock: {self.doSomething()})
volumeButtonHandler?.start(true)
...  
func doSomething() -> Void {  
...  
}