Add Example-iOS in ObjC

Summary:
Related issue: [#425](https://github.com/Instagram/IGListKit/issues/425)

- [ ] All tests pass. Demo project builds and runs.
- [ ] I added tests, an experiment, or detailed why my change isn't tested.
- [ ] I added an entry to the `CHANGELOG.md` for any breaking changes, enhancements, or bug fixes.
- [ ] I have reviewed the [contributing guide](https://github.com/Instagram/IGListKit/blob/master/.github/CONTRIBUTING.md)
Closes https://github.com/Instagram/IGListKit/pull/446

Differential Revision: D4589989

Pulled By: rnystrom

fbshipit-source-id: df91f10e0896dfe2f39a643f68e7ebd91e8461cb

Examples/Examples-iOS/IGListKitExamples/ViewControllers/DemosViewController.swift

@@ -37,6 +37,7 @@ final class DemosViewController: UIViewController, IGListAdapterDataSource {
         DemoItem(name: "Self-sizing cells", controllerClass: SelfSizingCellsViewController.self),
         DemoItem(name: "Display delegate", controllerClass: DisplayViewController.self),
         DemoItem(name: "Stacked Section Controllers", controllerClass: StackedViewController.self),
+        DemoItem(name: "Objc Demo", controllerClass: ObjcDemoViewController.self)
     ]
 
     override func viewDidLoad() {

Examples/Examples-iOS/IGListKitExamples/ViewControllers/IGListKitExamples-Bridging-Header.h

@@ -0,0 +1,16 @@
+/**
+ Copyright (c) 2016-present, Facebook, Inc. All rights reserved.
+ 
+ The examples provided by Facebook are for non-commercial testing and evaluation
+ purposes only. Facebook reserves all rights not expressly granted.
+ 
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#import "ObjcDemoViewController.h"
+

Examples/Examples-iOS/IGListKitExamples/ViewControllers/ObjcDemoViewController.h

@@ -0,0 +1,19 @@
+/**
+ Copyright (c) 2016-present, Facebook, Inc. All rights reserved.
+ 
+ The examples provided by Facebook are for non-commercial testing and evaluation
+ purposes only. Facebook reserves all rights not expressly granted.
+ 
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#import <UIKit/UIKit.h>
+
+@interface ObjcDemoViewController : UIViewController
+
+@end

Examples/Examples-iOS/IGListKitExamples/ViewControllers/ObjcDemoViewController.m

@@ -0,0 +1,133 @@
+/**
+ Copyright (c) 2016-present, Facebook, Inc. All rights reserved.
+ 
+ The examples provided by Facebook are for non-commercial testing and evaluation
+ purposes only. Facebook reserves all rights not expressly granted.
+ 
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#import "ObjcDemoViewController.h"
+#import <IGListKit/IGListKit.h>
+
+#import "UserInfoSectionController.h"
+#import "ImageSectionController.h"
+#import "InteractiveSectionController.h"
+#import "CommentSectionController.h"
+
+#import "UserInfo.h"
+#import "PhotoCell.h"
+
+@interface ObjcDemoViewController () <IGListAdapterDataSource>
+@property (nonatomic, strong) IGListCollectionView *collectionView;
+@property (nonatomic, strong) IGListAdapter *adapter;
+@property (nonatomic, strong) NSArray *data;
+@end
+
+@implementation ObjcDemoViewController
+
+- (void)viewDidLoad {
+    [super viewDidLoad];
+    [self setupUI];
+}
+
+- (void)viewDidLayoutSubviews {
+    [super viewDidLayoutSubviews];
+    self.collectionView.frame = self.view.bounds;
+}
+
+- (void)didReceiveMemoryWarning {
+    [super didReceiveMemoryWarning];
+}
+
+#pragma mark - setupUI
+
+- (void)setupUI {
+    
+    [self.view addSubview:self.collectionView];
+    
+    self.adapter.collectionView = self.collectionView;
+    self.adapter.dataSource = self;
+}
+
+#pragma mark - IGListAdapterDataSource
+
+- (NSArray<id<IGListDiffable>> *)objectsForListAdapter:(IGListAdapter *)listAdapter {
+    return self.data;
+}
+
+- (IGListSectionController<IGListSectionType> *)listAdapter:(IGListAdapter *)listAdapter sectionControllerForObject:(id)object {
+    if ([object isKindOfClass:[NSString class]]) {
+        if ([object isEqualToString:@"Image-Placeholder-String"]) {
+            return [[ImageSectionController alloc] init];
+        } else if ([object length]) {
+            return [[CommentSectionController alloc] init];
+        } else {
+            return [[InteractiveSectionController alloc] init];
+        }
+    } else {
+        return [[UserInfoSectionController alloc] init];
+    }
+}
+
+- (UIView *)emptyViewForListAdapter:(IGListAdapter *)listAdapter {
+    return nil;
+}
+
+#pragma mark - Custom Accessors
+
+- (IGListAdapter *)adapter {
+    if (!_adapter) {
+        _adapter = [[IGListAdapter alloc] initWithUpdater:[[IGListAdapterUpdater alloc] init]
+                                           viewController:self
+                                         workingRangeSize:0];
+    }
+    return _adapter;
+}
+
+- (IGListCollectionView *)collectionView {
+    if (!_collectionView) {
+        UICollectionViewLayout *layout = [[UICollectionViewFlowLayout alloc] init];
+        _collectionView = [[IGListCollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:layout];
+    }
+    return _collectionView;
+}
+
+- (NSArray *)data {
+    if (!_data) {
+        UserInfo *userA = [[UserInfo alloc] initWithName:@"userA"];
+        UserInfo *userB = [[UserInfo alloc] initWithName:@"userB"];
+        UserInfo *userC = [[UserInfo alloc] initWithName:@"userC"];
+        UserInfo *userD = [[UserInfo alloc] initWithName:@"userD"];
+        
+        _data = @[userA,
+                  @"Image-Placeholder-String",
+                  @"", @"Luminous triangle",
+                  @"Awesome",
+                  @"Super clean",
+                  @"Stunning shot",
+                  userB,
+                  @"Image-Placeholder-String",
+                  @"",
+                  @"The simplicity here is superb",
+                  @"thanks!", @"That's always so kind of you!",
+                  @"I think you might like this",
+                  userC,
+                  @"Image-Placeholder-String",
+                  @"",
+                  @"So good comment",
+                  userD,
+                  @"Image-Placeholder-String",
+                  @"",
+                  @"hope she might like it.",
+                  @"I love it."];
+    }
+    return _data;
+}
+
+@end