GADCustomEventExtras
@interface GADCustomEventExtras : NSObject <GADAdNetworkExtras>Create an instance of this class to set additional parameters for each custom event object. The additional parameters for a custom event are keyed by the custom event label. These extras are passed to your implementation of GADCustomEventBanner or GADCustomEventInterstitial.
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                  Set additional parameters for the custom event with label |label|. To remove additional parameters associated with |label|, pass in nil for |extras|. DeclarationSwift func setExtras(_ extras: [AnyHashable : Any]?, forLabel label: String)Objective-C - (void)setExtras:(nullable NSDictionary *)extras forLabel:(nonnull NSString *)label;
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                  Retrieve the extras for |label|. DeclarationSwift func extras(forLabel label: String) -> [AnyHashable : Any]?Objective-C - (nullable NSDictionary *)extrasForLabel:(nonnull NSString *)label;
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                  Removes all the extras set on this instance. DeclarationSwift func removeAllExtras()Objective-C - (void)removeAllExtras;
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                  Returns all the extras set on this instance. DeclarationSwift func allExtras() -> [AnyHashable : Any]Objective-C - (nonnull NSDictionary *)allExtras;