components/private/Overlay/src/MDCOverlayObserver.h

/*
 Copyright 2016-present the Material Components for iOS authors. All Rights Reserved.

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */

#import <UIKit/UIKit.h>

/**
 Class responsible for reporting changes to overlays on a given screen.
 */
@interface MDCOverlayObserver : NSObject

/**
 Returns the overlay observer for the given screen.

 If @c screen is nil, the main screen is used.
 */
+ (instancetype)observerForScreen:(UIScreen *)screen;

/**
 Adds a target/action pair to listen for changes to overlays.

 If an overlay is already showing when this method is called, then a call to the target/action will
 be made immediately with an unanimated transition.

 @param target The object which will be the target of @c action
 @param action The method to invoke on @c target. This method should take a single argument, an
               object that conforms to @c MDCOverlayTransitioning.
 */
- (void)addTarget:(id)target action:(SEL)action;

/**
 Prevents the given target/action pair from being notified of overlay changes.

 @param target The target to stop notifying of changes. If multiple @c actions have been
               registered, then @c target may still receive notifications via other selectors.
 @param action The method which will no longer be called when overlay changes occur.
 */
- (void)removeTarget:(id)target action:(SEL)action;

/**
 Prevents the given target from being notified of any overlay changes.

 @param target The target to stop notifying of changes. This will remove any and all target-action
               pairs registered via @c addTarget:action:.
 */
- (void)removeTarget:(id)target;

@end