Remove an existing UIAlertViews when invalidating the RCTAlertManager

Reviewed By: @nicklockwood

Differential Revision: D2456795

React/Modules/RCTAlertManager.h

@@ -10,7 +10,8 @@
 #import <UIKit/UIKit.h>
 
 #import "RCTBridgeModule.h"
+#import "RCTInvalidating.h"
 
-@interface RCTAlertManager : NSObject <RCTBridgeModule>
+@interface RCTAlertManager : NSObject <RCTBridgeModule, RCTInvalidating>
 
 @end

React/Modules/RCTAlertManager.m

@@ -40,6 +40,13 @@ RCT_EXPORT_MODULE()
   return dispatch_get_main_queue();
 }
 
+- (void)invalidate
+{
+    for (UIAlertView *alert in _alerts) {
+        [alert dismissWithClickedButtonIndex:0 animated:YES];
+    }
+}
+
 /**
  * @param {NSDictionary} args Dictionary of the form
  *