Background support when it was stopped

Pulsator/Pulsator.swift

@@ -24,7 +24,7 @@ public class Pulsator: CAReplicatorLayer {
  pulse.backgroundColor = backgroundColor
  let oldAlpha = alpha
  alpha = CGColorGetAlpha(backgroundColor)
- if animationGroup != nil && alpha != oldAlpha {
+ if alpha != oldAlpha {
  recreate()
  }
  }
@@ -83,9 +83,7 @@ public class Pulsator: CAReplicatorLayer {
  /// The value of this property should be ranging from @c 0 to @c 1 (exclusive).
  public var keyTimeForHalfOpacity: Float = 0.2 {
  didSet {
- if animationGroup != nil {
- recreate()
- }
+ recreate()
  }
  }
 
@@ -179,6 +177,7 @@ public class Pulsator: CAReplicatorLayer {
  // MARK: - Internal Methods
 
  internal func recreate() {
+ guard animationGroup != nil else { return } // Not need to be recreated.
  stop()
  let when = dispatch_time(DISPATCH_TIME_NOW, Int64(0.2 * double_t(NSEC_PER_SEC)))
  dispatch_after(when, dispatch_get_main_queue()) { () -> Void in