Do not emit events until JavaScript is ready

If the synchronizer is running in the background, but the app does a hot-reload, we need to stop sending events until JavaScript is ready again.

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- fixed: Pause synchronizer events until JavaScript is ready to receive them.
+
 ## 0.7.1 (2024-05-11)
 
 - fixed: Stop depending on the iOS-provided SQLite, which causes crashes on iOS 13-15 because it is too old.

ios/RNZcash.swift

@@ -72,6 +72,7 @@ let genericError = NSError(domain: "", code: 0)
 
 @objc(RNZcash)
 class RNZcash: RCTEventEmitter {
+  var hasListeners: Bool = false
 
   override static func requiresMainQueueSetup() -> Bool {
     return true
@@ -440,7 +441,17 @@ class RNZcash: RCTEventEmitter {
 
   // Events
   public func sendToJs(name: String, data: Any) {
-    self.sendEvent(withName: name, body: data)
+    if (hasListeners) {
+      self.sendEvent(withName: name, body: data)
+    }
+  }
+
+  override func startObserving() -> Void {
+    hasListeners = true
+  }
+
+  override func stopObserving() -> Void {
+    hasListeners = false
   }
 
   override func supportedEvents() -> [String] {