[Tabs] Add initial support for custom view. (#7678)

Creates basic support for a custom view property on UITabBarItem. Although not
a category on UITabBarItem, it can be used in the same places UITabBarItem can
be used. This will allow clients of MDCTabBarView to provide a custom view to
replace the default presentation of the title and image.

Closes #7676

components/Tabs/src/TabBarView/MDCTabBarItem.h

@@ -0,0 +1,24 @@
+// Copyright 2019-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>
+
+#import "MDCTabBarItemCustomViewing.h"
+
+/**
+ A subclass of @c UITabBarItem that supports a custom view property.
+ */
+__attribute__((objc_subclassing_restricted)) @interface MDCTabBarItem
+    : UITabBarItem<MDCTabBarItemCustomViewing>
+@end

components/Tabs/src/TabBarView/MDCTabBarItem.m

@@ -0,0 +1,21 @@
+// Copyright 2019-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 "MDCTabBarItem.h"
+
+@implementation MDCTabBarItem
+
+@synthesize mdc_customView = _mdc_customView;
+
+@end

components/Tabs/src/TabBarView/MDCTabBarItemCustomViewing.h

@@ -0,0 +1,31 @@
+// Copyright 2019-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 <Foundation/Foundation.h>
+
+#import "MDCTabBarSelectionIndicatorSupporting.h"
+
+/**
+ Defines the necessary APIs for MDCTabBarView to use a UITabBarItem for a custom view property.
+
+ @note Although UIKit defines such a property on @c UIBarButtonItem, no similar property is publicly
+ documented on @c UITabBarItem.
+ */
+@protocol MDCTabBarItemCustomViewing
+
+/** A custom view to be displayed for a tab bar item. */
+@property(nullable, nonatomic, strong)
+    UIView<MDCTabBarSelectionIndicatorSupporting> *mdc_customView;
+
+@end

components/Tabs/src/TabBarView/MDCTabBarSelectionIndicatorSupporting.h

@@ -0,0 +1,36 @@
+// Copyright 2019-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 <Foundation/Foundation.h>
+
+/**
+ A simple protocol that indicates the responder can be targeted by an
+ @c MDCTabBarSelectionIndicatorTemplate.
+
+ @seealso MDCTabBarIndicatorTemplate
+ */
+@protocol MDCTabBarSelectionIndicatorSupporting
+
+/**
+ The bounds of the receiver.
+ */
+@property(readonly) CGRect bounds;
+
+/**
+ The frame of the content of the receiver. Used to position the Selection Indicator relative to
+ the content.
+ */
+@property(readonly) CGRect contentFrame;
+
+@end

components/Tabs/src/TabBarView/MaterialTabs+TabBarView.h

@@ -12,4 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#import "MDCTabBarItem.h"
+#import "MDCTabBarItemCustomViewing.h"
+#import "MDCTabBarSelectionIndicatorSupporting.h"
 #import "MDCTabBarView.h"

components/Tabs/tests/unit/TabBarView/MDCTabBarItemTests.m

@@ -0,0 +1,48 @@
+// Copyright 2019-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 <XCTest/XCTest.h>
+
+#import "MaterialTabs+TabBarView.h"
+
+@interface MDCTabBarItemTestCustomViewTestFake : UIView <MDCTabBarSelectionIndicatorSupporting>
+@end
+
+@implementation MDCTabBarItemTestCustomViewTestFake
+
+- (CGRect)contentFrame {
+  return CGRectZero;
+}
+
+@end
+
+@interface MDCTabBarItemTests : XCTestCase
+@end
+
+@implementation MDCTabBarItemTests
+
+- (void)testGetterSetterForCustomView {
+  // Given
+  MDCTabBarItemTestCustomViewTestFake *customView =
+      [[MDCTabBarItemTestCustomViewTestFake alloc] init];
+  MDCTabBarItem *barItem = [[MDCTabBarItem alloc] init];
+
+  // When
+  barItem.mdc_customView = customView;
+
+  // Then
+  XCTAssertEqual(barItem.mdc_customView, customView);
+}
+
+@end