Delay iOS Resolver initialization

Delay iOS Resolver initialization until
1. Current active build target is iOS
2. When the editor is NOT in play mode

This is to prevent unnecessary initialization when the play mode start
and AppDomain reload.

Improves googlesamples#639

Bug: 154730431
Change-Id: Id5611bcfa4136e9808cc7d5fc9e832479622e8d1

Author: chkuang-g

source/IOSResolver/src/IOSResolver.cs

@@ -651,54 +651,90 @@ private static Assembly ResolveUnityEditoriOSXcodeExtension(
     static IOSResolver() {
         // Load log preferences.
         VerboseLoggingEnabled = VerboseLoggingEnabled;
+
         // NOTE: We can't reference the UnityEditor.iOS.Xcode module in this
         // method as the Mono runtime in Unity 4 and below requires all
         // dependencies of a method are loaded before the method is executed
         // so we install the DLL loader first then try using the Xcode module.
         RemapXcodeExtension();
+
+        // Cache the flag to prevent string comparison in every frame during
+        // PollOnUpdateUntilComplete()
+        bool isExecuteMethodEnabled =  ExecutionEnvironment.ExecuteMethodEnabled;
+
+        // Delay initialization until the build target is iOS and the editor is not in play mode.
+        RunOnMainThread.PollOnUpdateUntilComplete(() => {
+            if (EditorUserBuildSettings.activeBuildTarget != BuildTarget.iOS ||
+                EditorApplication.isPlayingOrWillChangePlaymode) {
+                // If Unity is launched with -executeMethod, in some Unity versions, editor
+                // update will never be called. As a result, PollOnUpdateUntilComplete() will
+                // attempt to call this poll function repeating on current thread until it returns
+                // true.  Therefore, return true immediately and stop the polling in executeMethod
+                // mode.
+                return isExecuteMethodEnabled;
+            }
+            Initialize();
+            return true;
+        });
+    }
+
+    /// <summary>
+    /// Whether iOSResolver have been initialized.
+    /// </summary>
+    private static bool isInitialized = false;
+
+    /// <summary>
+    /// Initialize the module. This should be called on the main thread only if
+    /// current active build target is iOS and not in play mode.
+    /// </summary>
+    private static void Initialize() {
+        if (isInitialized) return;
+
+        if ( EditorUserBuildSettings.activeBuildTarget != BuildTarget.iOS ) {
+            throw new Exception("IOSResolver.Initialize() is called when active build target " +
+                    "is not iOS. This should never happen.  If it does, please report to the " +
+                    "developer.");
+        }
+
         // NOTE: It's not possible to catch exceptions a missing reference
         // to the UnityEditor.iOS.Xcode assembly in this method as the runtime
         // will attempt to load the assembly before the method is executed so
         // we handle exceptions here.
         try {
             InitializeTargetName();
         } catch (Exception exception) {
-            if (EditorUserBuildSettings.activeBuildTarget == BuildTarget.iOS) {
-                Log("Failed: " + exception.ToString(), level: LogLevel.Error);
-                if (exception is FileNotFoundException ||
-                    exception is TypeInitializationException ||
-                    exception is TargetInvocationException) {
-                    // It's likely we failed to load the iOS Xcode extension.
-                    Debug.LogWarning(
-                        "Failed to load the " +
-                        "UnityEditor.iOS.Extensions.Xcode dll.  " +
-                        "Is iOS support installed?");
-                } else {
-                    throw exception;
-                }
+            Log("Failed: " + exception.ToString(), level: LogLevel.Error);
+            if (exception is FileNotFoundException ||
+                exception is TypeInitializationException ||
+                exception is TargetInvocationException) {
+                // It's likely we failed to load the iOS Xcode extension.
+                Debug.LogWarning(
+                    "Failed to load the " +
+                    "UnityEditor.iOS.Extensions.Xcode dll.  " +
+                    "Is iOS support installed?");
+            } else {
+                throw exception;
             }
         }
 
         // If Cocoapod tool auto-installation is enabled try installing on the first update of
         // the editor when the editor environment has been initialized.
-        if (EditorUserBuildSettings.activeBuildTarget == BuildTarget.iOS &&
-            AutoPodToolInstallInEditorEnabled && CocoapodsIntegrationEnabled &&
+        if (AutoPodToolInstallInEditorEnabled && CocoapodsIntegrationEnabled &&
             !ExecutionEnvironment.InBatchMode) {
-            RunOnMainThread.Run(() => { AutoInstallCocoapods(); }, runNow: false);
+            AutoInstallCocoapods();
         }
         // Install / remove target SDK property poller.
         SetEnablePollTargetSdk(PodfileGenerationEnabled);
         // Load XML dependencies on the next editor update.
         if (PodfileGenerationEnabled) {
-            RunOnMainThread.Run(RefreshXmlDependencies, runNow: false);
+            RefreshXmlDependencies();
         }
 
         // Prompt the user to use workspaces if they aren't at least using project level
         // integration.
-        if (EditorUserBuildSettings.activeBuildTarget == BuildTarget.iOS &&
-            (CocoapodsIntegrationMethod)settings.GetInt(PREFERENCE_COCOAPODS_INTEGRATION_METHOD,
+        if ((CocoapodsIntegrationMethod)settings.GetInt(PREFERENCE_COCOAPODS_INTEGRATION_METHOD,
                 CocoapodsIntegrationUpgradeDefault) == CocoapodsIntegrationMethod.None &&
-            !ExecutionEnvironment.InBatchMode && !UpgradeToWorkspaceWarningDisabled) {
+                !ExecutionEnvironment.InBatchMode && !UpgradeToWorkspaceWarningDisabled) {
 
             DialogWindow.Display(
                 "Warning: CocoaPods integration is disabled!",
@@ -721,6 +757,9 @@ exception is TypeInitializationException ||
                     }
                 });
         }
+        isInitialized = true;
+
+        Log("IOSResolver Initialized", verbose: true);
     }
 
     /// <summary>