let the boost container support the observer to app's enter background and...

let the boost container support the observer to app's enter background and will enter foreground notification.

ios/Classes/1.5/FLB2FlutterApplication.m

@@ -76,13 +76,24 @@
         _manager = [FLB2FlutterContainerManager new];
         _pageResultCallbacks = NSMutableDictionary.new;
         _callbackCache = NSMutableDictionary.new;
+        
+        [[NSNotificationCenter defaultCenter] addObserver:self
+                                                 selector:@selector(applicationWillEnterForeground:)
+                                                     name:UIApplicationWillEnterForegroundNotification
+                                                   object:nil];
+        
+        [[NSNotificationCenter defaultCenter] addObserver:self
+                                                 selector:@selector(applicationDidEnterBackground:)
+                                                     name:UIApplicationDidEnterBackgroundNotification
+                                                   object:nil];
     }
     return self;
 }
 
 - (void)dealloc
 {
-    [[NSNotificationCenter defaultCenter] removeObserver:self];
+    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationWillEnterForegroundNotification object:nil];
+    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidEnterBackgroundNotification object:nil];
 }
 
 - (UIView *)flutterView
@@ -90,6 +101,13 @@
     return [self flutterViewController].view;
 }
 
+- (void)applicationDidEnterBackground:(UIApplication *)application {
+    [self.viewProvider didEnterBackground];
+}
+
+- (void)applicationWillEnterForeground:(UIApplication *)application {
+    [self.viewProvider willEnterForeground];
+}
 
 - (BOOL)contains:(id<FLBFlutterContainer>)vc
 {

ios/Classes/1.5/FLB2FlutterEngine.m

@@ -25,6 +25,7 @@
 #import "FLB2FlutterEngine.h"
 #import <Flutter/Flutter.h>
 #import "FLB2FlutterViewContainer.h"
+#import "BoostMessageChannel.h"
 
 
 @interface FLB2FlutterEngine()
@@ -87,6 +88,17 @@
 }
 
 
+- (void)didEnterBackground
+{
+    [BoostMessageChannel sendEvent:@"background"
+                         arguments:nil];
+}
+
+- (void)willEnterForeground
+{
+    [BoostMessageChannel sendEvent:@"foreground"
+                         arguments:nil];
+}
 
 - (FlutterEngine *)engine
 {

ios/Classes/Boost/FLB2FlutterProvider.h

@@ -37,5 +37,7 @@ NS_ASSUME_NONNULL_BEGIN
 - (void)pause;
 - (void)resume;
 - (void)inactive;
+- (void)didEnterBackground;
+- (void)willEnterForeground;
 @end
 NS_ASSUME_NONNULL_END