get rid of the singleton function of FLBFlutterApplication

ios/Classes/Boost/FlutterBoostPlugin.m

@@ -111,26 +111,16 @@
     return _instance;
 }
 
-
-- (id<FLBFlutterApplicationInterface>)application
-{
-    return _application;
-}
-
-
-- (id<FLBAbstractFactory>)factory
-{
-    return _factory;
-}
-
 - (void)startFlutterWithPlatform:(id<FLBPlatform>)platform
                          onStart:(void (^)(FlutterEngine *engine))callback;
 {
     static dispatch_once_t onceToken;
+    __weak __typeof__(self) weakSelf = self;
     dispatch_once(&onceToken, ^{
-        self->_factory = FLBFactory.new;
-        self->_application = [self->_factory createApplication:platform];
-        [self->_application startFlutterWithPlatform:platform
+        __strong __typeof__(weakSelf) self = weakSelf;
+        self.factory = FLBFactory.new;
+        self.application = [self->_factory createApplication:platform];
+        [self.application startFlutterWithPlatform:platform
                                        onStart:callback];
     });
 }

ios/Classes/Boost/FlutterBoostPlugin_private.h

@@ -26,14 +26,11 @@
 #import "FLBFlutterApplicationInterface.h"
 #import "FLBAbstractFactory.h"
 #import "FlutterBoostPlugin.h"
-@interface FlutterBoostPlugin(){
-    id<FLBFlutterApplicationInterface> _application;
-    id<FLBAbstractFactory> _factory;
-}
+@interface FlutterBoostPlugin()
+@property (nonatomic,strong) id<FLBFlutterApplicationInterface> application;
+@property (nonatomic,strong) id<FLBAbstractFactory> factory;
 @property (nonatomic,strong) FlutterMethodChannel *methodChannel;
 @property (nonatomic,copy) NSString *fPageId;
 @property (nonatomic,copy) NSString *fPagename;
 @property (nonatomic,strong) NSDictionary *fParams;
-- (id<FLBFlutterApplicationInterface>)application;
-- (id<FLBAbstractFactory>)factory;
 @end

ios/Classes/Engine/FLBFactory.m

@@ -30,7 +30,7 @@
 
 - (id<FLBFlutterApplicationInterface>)createApplication:(id<FLBPlatform>)platform
 {
-    return [FLBFlutterApplication sharedApplication];
+    return [FLBFlutterApplication new];
 }
 
 - (id<FLBFlutterContainer>)createFlutterContainer

ios/Classes/Engine/FLBFlutterApplication.h

@@ -30,6 +30,5 @@
 
 NS_ASSUME_NONNULL_BEGIN
 @interface FLBFlutterApplication : NSObject<FLBFlutterApplicationInterface>
-+ (FLBFlutterApplication *)sharedApplication;
 @end
 NS_ASSUME_NONNULL_END

ios/Classes/Engine/FLBFlutterApplication.m

@@ -39,16 +39,6 @@
 @implementation FLBFlutterApplication
 @synthesize platform;
 
-+ (FLBFlutterApplication *)sharedApplication
-{
-    static FLBFlutterApplication *instance = nil;
-    static dispatch_once_t onceToken;
-    dispatch_once(&onceToken, ^{
-        instance = [self new];
-    });
-    return instance;
-}
-
 - (BOOL)isRunning
 {
     return _isRunning;