iOS:Add loopback launch argument functionality in AppRTCMobile.

webrtc/examples/objc/AppRTCMobile/ios/ARDMainViewController.m

 /*
  *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #import "ARDMainViewController.h"
 
 #import <AVFoundation/AVFoundation.h>
 
 #import "WebRTC/RTCDispatcher.h"
 #import "WebRTC/RTCLogging.h"
 #import "webrtc/modules/audio_device/ios/objc/RTCAudioSession.h"
 #import "webrtc/modules/audio_device/ios/objc/RTCAudioSessionConfiguration.h"
 
 #import "ARDAppClient.h"
 #import "ARDMainView.h"
 #import "ARDSettingsModel.h"
 #import "ARDSettingsViewController.h"
 #import "ARDVideoCallViewController.h"
 
 static NSString *const barButtonImageString = @"ic_settings_black_24dp.png";
 
+// Launch argument to be passed to indicate that the app should start loopback immediatly
+static NSString *const loopbackLaunchProcessArgument = @"loopback";
+
 @interface ARDMainViewController () <
     ARDMainViewDelegate,
     ARDVideoCallViewControllerDelegate,
     RTCAudioSessionDelegate>
 @end
 
 @implementation ARDMainViewController {
   ARDMainView *_mainView;
   AVAudioPlayer *_audioPlayer;
   BOOL _useManualAudio;
 }
 
+- (void)viewDidLoad {
+  [super viewDidLoad];
+  if ([[[NSProcessInfo processInfo] arguments] containsObject:loopbackLaunchProcessArgument]) {
+    [self mainView:nil
+                 didInputRoom:@""
+                   isLoopback:YES
+                  isAudioOnly:NO
+            shouldMakeAecDump:NO
+        shouldUseLevelControl:NO
+               useManualAudio:NO];
+  }
+}
+
 - (void)loadView {
   self.title = @"AppRTC Mobile";
   _mainView = [[ARDMainView alloc] initWithFrame:CGRectZero];
   _mainView.delegate = self;
   self.view = _mainView;
   [self addSettingsBarButton];
 
   RTCAudioSessionConfiguration *webRTCConfig =
       [RTCAudioSessionConfiguration webRTCConfiguration];
   webRTCConfig.categoryOptions = webRTCConfig.categoryOptions |
       AVAudioSessionCategoryOptionDefaultToSpeaker;
   [RTCAudioSessionConfiguration setWebRTCConfiguration:webRTCConfig];
 
   RTCAudioSession *session = [RTCAudioSession sharedInstance];
   [session addDelegate:self];
 
   [self configureAudioSession];
   [self setupAudioPlayer];
 }
 
 - (void)addSettingsBarButton {
   UIBarButtonItem *settingsButton =
       [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:barButtonImageString]
                                        style:UIBarButtonItemStylePlain
                                       target:self
                                       action:@selector(showSettings:)];
   self.navigationItem.rightBarButtonItem = settingsButton;
 }
 
++ (NSString *)loopbackRoomString {
+  NSString *loopbackRoomString =
+      [[NSUUID UUID].UUIDString stringByReplacingOccurrencesOfString:@"-" withString:@""];
+  return loopbackRoomString;
+}
+
 #pragma mark - ARDMainViewDelegate
 
 - (void)mainView:(ARDMainView *)mainView
              didInputRoom:(NSString *)room
                isLoopback:(BOOL)isLoopback
               isAudioOnly:(BOOL)isAudioOnly
         shouldMakeAecDump:(BOOL)shouldMakeAecDump
     shouldUseLevelControl:(BOOL)shouldUseLevelControl
            useManualAudio:(BOOL)useManualAudio {
   if (!room.length) {
-    [self showAlertWithMessage:@"Missing room name."];
-    return;
+    if (isLoopback) {
+      // If this is a loopback call, allow a generated room name.
+      room = [[self class] loopbackRoomString];
+    } else {
+      [self showAlertWithMessage:@"Missing room name."];
+      return;
+    }
   }
   // Trim whitespaces.
   NSCharacterSet *whitespaceSet = [NSCharacterSet whitespaceCharacterSet];
   NSString *trimmedRoom = [room stringByTrimmingCharactersInSet:whitespaceSet];
 
   // Check that room name is valid.
   NSError *error = nil;
   NSRegularExpressionOptions options = NSRegularExpressionCaseInsensitive;
   NSRegularExpression *regex =
       [NSRegularExpression regularExpressionWithPattern:@"\\w+"
@@ skipping 139 matching lines @@
 - (void)showAlertWithMessage:(NSString*)message {
   UIAlertView* alertView = [[UIAlertView alloc] initWithTitle:nil
                                                       message:message
                                                      delegate:nil
                                             cancelButtonTitle:@"OK"
                                             otherButtonTitles:nil];
   [alertView show];
 }
 
 @end