added extra checks for main thread, and some badges to README

README.md

@@ -2,6 +2,9 @@
 
 RKPointPin is a UIView which sticks to an `ARView` and points at a chosen entity within the scene, with options to hide the pin when near the center of the screen, or perform any custom actions.
 
+[![Swift Package Manager](https://img.shields.io/badge/Swift_Package_Manager-v1.0.0-orange.svg?style=flat)](https://github.com/apple/swift-package-manager)
+[![Swift 5.2](https://img.shields.io/badge/Swift-5.2-orange.svg?style=flat)](https://swift.org/)
+
 ![RKPointPin Example](media/pin_512.gif)
 
 ## Minimum Requirements
@@ -29,4 +32,4 @@ self.arView.addSubview(rkPin)
 rkPin.targetEntity = boxEntity
 ```
 
-By default the RKPointPin will be visible all the time, but if you want the pin to hide when in the center, set the `focusPercentage` to a value ranging from 0 to 1. If  `focusPercentage` is set to 1, then the pin will only appear when the `targetEntity` is outside of the view, as everything from the edges inwards is considered the focus area. 
+By default the RKPointPin will be visible all the time, but if you want the pin to hide when in the center, set the `focusPercentage` to a value ranging from 0 to 1. If  `focusPercentage` is set to 1, then the pin will only appear when the `targetEntity` is outside of the view, as everything from the edges inwards is considered the focus area.

Sources/RKPointPin/RKPointPin.swift

@@ -111,7 +111,14 @@ public class RKPointPin: UIView {
 
   private func resetCancellable() {
     self.cancellable?.cancel()
-    guard let arView = self.arView, self.targetEntity != nil else {
+    if self.targetEntity == nil {
+      return
+    }
+    if !Thread.isMainThread {
+      print("RKPointPin ERROR: targetEntity should set from main thread")
+      return
+    }
+    guard let arView = self.arView else {
       return
     }
     self.cancellable = arView.scene.subscribe(
@@ -168,7 +175,7 @@ public class RKPointPin: UIView {
 
   private func updatePos() {
     if !Thread.isMainThread {
-      print("RKPointPin: Should be on main thread")
+      print("RKPointPin ERROR: Should be on main thread")
       return
     }
     guard let arView = self.arView else {