#200 optimize for zero listeners on ios

Author: plrthink

ios/RNZipArchive.m

@@ -16,11 +16,26 @@
 #endif
 
 @implementation RNZipArchive
+{
+  bool hasListeners;
+}
 
 @synthesize bridge = _bridge;
 
 RCT_EXPORT_MODULE();
 
+// Will be called when this module's first listener is added.
+-(void)startObserving {
+    hasListeners = YES;
+    // Set up any upstream listeners or background tasks as necessary
+}
+
+// Will be called when this module's last listener is removed, or on dealloc.
+-(void)stopObserving {
+    hasListeners = NO;
+    // Remove upstream listeners, stop unnecessary background tasks
+}
+
 - (NSArray<NSString *> *)supportedEvents
 {
   return @[@"zipArchiveProgressEvent"];
@@ -201,7 +216,9 @@ - (void)setProgressHandler {
 }
 
 - (void)dispatchProgessEvent:(float)progress processedFilePath:(NSString *)processedFilePath {
-    [self sendEventWithName:@"zipArchiveProgressEvent" body:@{@"progress": @(progress), @"filePath": processedFilePath}];
+    if (hasListeners) {
+        [self sendEventWithName:@"zipArchiveProgressEvent" body:@{@"progress": @(progress), @"filePath": processedFilePath}];
+    }
 }
 
 @end