release extMsg after fetched

android/src/main/kotlin/com/jarvan/fluwx/FluwxPlugin.kt

@@ -109,6 +109,7 @@ class FluwxPlugin : FlutterPlugin, MethodCallHandler, ActivityAware,PluginRegist
 
     private fun getExtMsg(result: MethodChannel.Result) {
         result.success(extMsg)
+        extMsg = null
     }
 
     private fun pay(call: MethodCall, result: MethodChannel.Result) {

ios/Classes/FluwxPlugin.m

@@ -198,6 +198,7 @@ FlutterMethodChannel *channel = nil;
 
 - (void)handelGetExtMsgWithCall:(FlutterMethodCall *)call result:(FlutterResult)result {
     result(self.extMsg);
+    self.extMsg=nil;
 }