Add ability to get ProjectInstance objects (#41)

Author: jeffkl

src/MSBuildProjectCreator.UnitTests/ProjectTests.cs

@@ -12,6 +12,16 @@ namespace Microsoft.Build.Utilities.ProjectCreation.UnitTests
 {
     public class ProjectTests : MSBuildTestBase
     {
+        [Fact]
+        public void ProjectInstanceGetsCorrectObject()
+        {
+            ProjectCreator.Create()
+                .Property("FA7AA8A112DA480AA2591A7FF619B05A", "43EEA58D938C4C6A9060816155FD5FA9")
+                .ProjectInstance
+                .GetPropertyValue("FA7AA8A112DA480AA2591A7FF619B05A")
+                .ShouldBe("43EEA58D938C4C6A9060816155FD5FA9");
+        }
+
         [Fact]
         public void ProjectIsReEvaluated()
         {

src/MSBuildProjectCreator/ProjectCreator.Project.cs

@@ -3,6 +3,8 @@
 // Licensed under the MIT license.
 
 using Microsoft.Build.Evaluation;
+using Microsoft.Build.Evaluation.Context;
+using Microsoft.Build.Execution;
 using System;
 using System.Collections.Generic;
 
@@ -20,6 +22,11 @@ public partial class ProjectCreator
         /// </summary>
         private Project _project;
 
+        /// <summary>
+        /// Stores the <see cref="ProjectInstance" /> for the current project.
+        /// </summary>
+        private ProjectInstance _projectInstance;
+
         /// <summary>
         /// Gets the <see cref="Project"/> instance for the current project.  The project is re-evaluated if necessary every time this property is accessed.
         /// </summary>
@@ -38,6 +45,11 @@ public Project Project
             }
         }
 
+        /// <summary>
+        /// Gets the <see cref="ProjectInstance" /> for the current project.
+        /// </summary>
+        public ProjectInstance ProjectInstance => _projectInstance ?? (_projectInstance = Project.CreateProjectInstance());
+
         /// <summary>
         /// Gets a <see cref="Project"/> instance from the current project.
         /// </summary>
@@ -97,5 +109,22 @@ public ProjectCreator TryGetProject(
 
             return this;
         }
+
+        /// <summary>
+        /// Gets a <see cref="ProjectInstance" /> from the current project.
+        /// </summary>
+        /// <param name="projectInstance">Receives the <see cref="ProjectInstance" />.</param>
+        /// <param name="projectInstanceSettings">Optional <see cref="ProjectInstanceSettings" /> to use when creating the project instance.</param>
+        /// <param name="evaluationContext">Optional <see cref="EvaluationContext" /> to use when creating the project instance.</param>
+        /// <returns>The current <see cref="ProjectCreator"/>.</returns>
+        public ProjectCreator TryGetProjectInstance(
+            out ProjectInstance projectInstance,
+            ProjectInstanceSettings projectInstanceSettings = ProjectInstanceSettings.None,
+            EvaluationContext evaluationContext = null)
+        {
+            projectInstance = Project.CreateProjectInstance(projectInstanceSettings, evaluationContext);
+
+            return this;
+        }
     }
 }