Fix AppInstance key reregistration issue

dev/AppLifecycle/SharedMemory.h

@@ -82,7 +82,7 @@ class SharedMemory
 
     bool IsValid()
     {
-        return (m_name.size() != 0);
+        return (m_name.size() != 0) && (m_view != nullptr);
     }
 
 protected:

test/AppLifecycle/AppInstanceRegisterKeyTests.cpp

@@ -0,0 +1,65 @@
+// Copyright (c) Microsoft Corporation and Contributors.
+// Licensed under the MIT License.
+
+#include "pch.h"
+#include <testdef.h>
+#include "Shared.h"
+
+using namespace WEX::Common;
+using namespace WEX::Logging;
+using namespace WEX::TestExecution;
+
+using namespace winrt;
+using namespace winrt::Microsoft::Windows::AppLifecycle;
+using namespace winrt::Windows::ApplicationModel::Activation;
+using namespace winrt::Windows::Foundation;
+using namespace winrt::Windows::Foundation::Collections;
+using namespace winrt::Windows::Management::Deployment;
+using namespace winrt::Windows::Storage;
+using namespace winrt::Windows::System;
+
+namespace Test::AppLifecycle
+{
+    class AppInstanceRegisterKeyTests
+    {
+    private:
+        const std::wstring c_testKeyName = L"TestKey_ReRegister";
+
+    public:
+        BEGIN_TEST_CLASS(AppInstanceRegisterKeyTests)
+            TEST_CLASS_PROPERTY(L"ThreadingModel", L"MTA")
+            TEST_CLASS_PROPERTY(L"RunAs:Class", L"RestrictedUser")
+        END_TEST_CLASS()
+
+        TEST_CLASS_SETUP(ClassInit)
+        {
+            ::Test::Bootstrap::Setup();
+            return true;
+        }
+
+        TEST_CLASS_CLEANUP(ClassUninit)
+        {
+            ::Test::Bootstrap::Cleanup();
+            return true;
+        }
+
+        TEST_METHOD(UnregisterAndReRegisterKey)
+        {
+            // First register a key
+            auto instance = AppInstance::FindOrRegisterForKey(c_testKeyName);
+            VERIFY_IS_NOT_NULL(instance);
+            VERIFY_IS_TRUE(instance.IsCurrent());
+            VERIFY_ARE_EQUAL(instance.Key(), c_testKeyName);
+
+            // Unregister the key
+            instance.UnregisterKey();
+            VERIFY_ARE_EQUAL(instance.Key(), L"");
+
+            // Re-register the same key
+            auto reRegisteredInstance = AppInstance::FindOrRegisterForKey(c_testKeyName);
+            VERIFY_IS_NOT_NULL(reRegisteredInstance);
+            VERIFY_IS_TRUE(reRegisteredInstance.IsCurrent());
+            VERIFY_ARE_EQUAL(reRegisteredInstance.Key(), c_testKeyName);
+        }
+    };
+}