Use Apple recommended way to weakly link classes

Compare https://developer.apple.com/library/ios/documentation/DeveloperTools/Conceptual/cross_development/Using/using.html

Classes/BITAuthenticator.m

@@ -337,8 +337,7 @@ static unsigned char kBITPNGEndChunk[4] = {0x49, 0x45, 0x4e, 0x44};
     return;
   }
   
-  id nsurlsessionClass = NSClassFromString(@"NSURLSessionUploadTask");
-  BOOL isSessionSupported = (nsurlsessionClass && !bit_isRunningInAppExtension());
+  BOOL isSessionSupported = ([NSURLSessionDataTask class] && !bit_isRunningInAppExtension());
   [self validateWithCompletion:completion sessionSupported:isSessionSupported];
 }
 
@@ -468,8 +467,7 @@ static unsigned char kBITPNGEndChunk[4] = {0x49, 0x45, 0x4e, 0x44};
   
   
   
-  id nsurlsessionClass = NSClassFromString(@"NSURLSessionUploadTask");
-  BOOL isURLSessionSupported = (nsurlsessionClass && !bit_isRunningInAppExtension());
+  BOOL isURLSessionSupported = ([NSURLSessionDataTask class] && !bit_isRunningInAppExtension());
   [self authenticationViewController:viewController handleAuthenticationWithEmail:email request:request urlSessionSupported:isURLSessionSupported completion:completion];
 }
 

Classes/BITCrashManager.m

@@ -1664,8 +1664,7 @@ static void uncaught_cxx_exception_handler(const BITCrashUncaughtCXXExceptionInf
 - (void)sendCrashReportWithFilename:(NSString *)filename xml:(NSString*)xml attachment:(BITHockeyAttachment *)attachment {
   BOOL sendingWithURLSession = NO;
   
-  id nsurlsessionClass = NSClassFromString(@"NSURLSessionUploadTask");
-  if (nsurlsessionClass && !bit_isRunningInAppExtension()) {
+  if ([NSURLSessionTask class] && !bit_isRunningInAppExtension()) {
     NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
     __block NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration];
     

Classes/BITFeedbackListViewController.m

@@ -151,8 +151,7 @@
     //    self.view.backgroundColor = DEFAULT_BACKGROUNDCOLOR_OS7;
   }
   
-  id refreshClass = NSClassFromString(@"UIRefreshControl");
-  if (refreshClass) {
+  if ([UIRefreshControl class]) {
     self.refreshControl = [[UIRefreshControl alloc] init];
     [self.refreshControl addTarget:self action:@selector(reloadList) forControlEvents:UIControlEventValueChanged];
   } else {
@@ -163,8 +162,7 @@
 }
 
 - (void)startLoadingIndicator {
-  id refreshClass = NSClassFromString(@"UIRefreshControl");
-  if (refreshClass) {
+  if ([UIRefreshControl class]) {
     [self.refreshControl beginRefreshing];
   } else {
     self.navigationItem.rightBarButtonItem.enabled = NO;
@@ -172,8 +170,7 @@
 }
 
 - (void)stopLoadingIndicator {
-  id refreshClass = NSClassFromString(@"UIRefreshControl");
-  if (refreshClass) {
+  if ([UIRefreshControl class]) {
     [self.refreshControl endRefreshing];
   } else {
     self.navigationItem.rightBarButtonItem.enabled = YES;
@@ -181,8 +178,7 @@
 }
 
 - (BOOL)isRefreshingWithNewControl {
-  id refreshClass = NSClassFromString(@"UIRefreshControl");
-  if (refreshClass) {
+  if ([UIRefreshControl class]) {
     return [self.refreshControl isRefreshing];
   }
   return NO;
@@ -717,8 +713,7 @@
         attachment.isLoading = YES;
         NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:attachment.sourceURL]];
         __weak typeof (self) weakSelf = self;
-        id nsurlsessionClass = NSClassFromString(@"NSURLSessionDataTask");
-        if (nsurlsessionClass && !bit_isRunningInAppExtension()) {
+        if ([NSURLSessionDataTask class] && !bit_isRunningInAppExtension()) {
           NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
           __block NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration];
           
@@ -991,8 +986,7 @@
       NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:attachment.sourceURL]];
       
       __weak typeof (self) weakSelf = self;
-      id nsurlsessionClass = NSClassFromString(@"NSURLSessionDataTask");
-      if (nsurlsessionClass && !bit_isRunningInAppExtension()) {
+      if ([NSURLSessionDataTask class] && !bit_isRunningInAppExtension()) {
         NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
         __block NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration];
         

Classes/BITFeedbackManager.m

@@ -947,8 +947,7 @@ NSString *const kBITFeedbackUpdateAttachmentThumbnail = @"BITFeedbackUpdateAttac
     [request setHTTPBody:postBody];
   }
   __weak typeof (self) weakSelf = self;
-  id nsurlsessionClass = NSClassFromString(@"NSURLSessionDataTask");
-  if (nsurlsessionClass && !bit_isRunningInAppExtension()) {
+  if ([NSURLSessionDataTask class] && !bit_isRunningInAppExtension()) {
     NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
     __block NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration];
     

Classes/BITHockeyHelper.m

@@ -173,8 +173,7 @@ NSString *bit_UUIDPreiOS6(void) {
 NSString *bit_UUID(void) {
   NSString *resultUUID = nil;
   
-  id uuidClass = NSClassFromString(@"NSUUID");
-  if (uuidClass) {
+  if ([NSUUID class]) {
     resultUUID = [[NSUUID UUID] UUIDString];
   } else {
     resultUUID = bit_UUIDPreiOS6();

Classes/BITHockeyManager.m

@@ -542,8 +542,7 @@ bitstadium_info_t bitstadium_library_info __attribute__((section("__TEXT,__bit_h
                            @"bundle_version": [[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleVersion"]
                            };
   
-  id nsurlsessionClass = NSClassFromString(@"NSURLSessionUploadTask");
-  if (nsurlsessionClass && !bit_isRunningInAppExtension()) {
+  if ([NSURLSessionTask class] && !bit_isRunningInAppExtension()) {
     NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
     __block NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration];
     NSURLRequest *request = [[self hockeyAppClient] requestWithMethod:@"POST" path:integrationPath parameters:params];

Classes/BITStoreUpdateManager.m

@@ -353,8 +353,7 @@
   [request setValue:@"gzip" forHTTPHeaderField:@"Accept-Encoding"];
   
   __weak typeof (self) weakSelf = self;
-  id nsurlsessionClass = NSClassFromString(@"NSURLSessionUploadTask");
-  if (nsurlsessionClass && !bit_isRunningInAppExtension()) {
+  if ([NSURLSessionTask class] && !bit_isRunningInAppExtension()) {
     NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
     __block NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration];
     

Classes/BITUpdateManager.m

@@ -888,8 +888,7 @@ typedef NS_ENUM(NSInteger, BITUpdateAlertViewTag) {
   [request setValue:@"Hockey/iOS" forHTTPHeaderField:@"User-Agent"];
   [request setValue:@"gzip" forHTTPHeaderField:@"Accept-Encoding"];
   
-  id nsurlsessionClass = NSClassFromString(@"NSURLSessionDataTask");
-  if (nsurlsessionClass && !bit_isRunningInAppExtension()) {
+  if ([NSURLSessionDataTask class] && !bit_isRunningInAppExtension()) {
     NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
     NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration delegate:(id<NSURLSessionDelegate>)self delegateQueue:nil];