Changed Contracts to if-throw-else as requested

Changed use of nullable return types to throw exceptions instead of returning null

SpotifyAPI.Example/App.config

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8" ?>
 <configuration>
-    <startup> 
+  <startup>
-        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
+    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
-    </startup>
+  </startup>
 </configuration>

SpotifyAPI.Example/LocalControl.cs

@@ -1,10 +1,10 @@
-using System;
+using SpotifyAPI.Local;
+using SpotifyAPI.Local.Enums;
+using SpotifyAPI.Local.Models;
+using System;
 using System.Diagnostics;
 using System.Globalization;
 using System.Windows.Forms;
-using SpotifyAPI.Local;
-using SpotifyAPI.Local.Enums;
-using SpotifyAPI.Local.Models;
 
 namespace SpotifyAPI.Example
 {
@@ -102,23 +102,23 @@ namespace SpotifyAPI.Example
             isPlayingLabel.Text = playing.ToString();
         }
 
-        void _spotify_OnVolumeChange(VolumeChangeEventArgs e)
+        private void _spotify_OnVolumeChange(VolumeChangeEventArgs e)
         {
-            volumeLabel.Text = (e.NewVolume*100).ToString(CultureInfo.InvariantCulture);
+            volumeLabel.Text = (e.NewVolume * 100).ToString(CultureInfo.InvariantCulture);
         }
 
-        void _spotify_OnTrackTimeChange(TrackTimeChangeEventArgs e)
+        private void _spotify_OnTrackTimeChange(TrackTimeChangeEventArgs e)
         {
             timeLabel.Text = FormatTime(e.TrackTime) + "/" + FormatTime(_currentTrack.Length);
-            timeProgressBar.Value = (int) e.TrackTime;
+            timeProgressBar.Value = (int)e.TrackTime;
         }
 
-        void _spotify_OnTrackChange(TrackChangeEventArgs e)
+        private void _spotify_OnTrackChange(TrackChangeEventArgs e)
         {
             UpdateTrack(e.NewTrack);
         }
 
-        void _spotify_OnPlayStateChange(PlayStateEventArgs e)
+        private void _spotify_OnPlayStateChange(PlayStateEventArgs e)
         {
             UpdatePlayingStatus(e.Playing);
         }

SpotifyAPI.Example/Program.cs

@@ -1,18 +1,15 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Threading.Tasks;
 using System.Windows.Forms;
 
 namespace SpotifyAPI.Example
 {
-    static class Program
+    internal static class Program
     {
         /// <summary>
         /// Der Haupteinstiegspunkt für die Anwendung.
         /// </summary>
         [STAThread]
-        static void Main()
+        private static void Main()
         {
             Application.EnableVisualStyles();
             Application.SetCompatibleTextRenderingDefault(false);

SpotifyAPI.Example/Properties/AssemblyInfo.cs

@@ -1,5 +1,4 @@
 using System.Reflection;
-using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
 // Allgemeine Informationen über eine Assembly werden über die folgenden

SpotifyAPI.Example/WebControl.cs

@@ -1,14 +1,13 @@
-using System;
+using SpotifyAPI.Web;
+using SpotifyAPI.Web.Auth;
+using SpotifyAPI.Web.Enums;
+using SpotifyAPI.Web.Models;
+using System;
 using System.Collections.Generic;
-using System.Drawing;
 using System.IO;
 using System.Linq;
 using System.Net;
 using System.Windows.Forms;
-using SpotifyAPI.Web;
-using SpotifyAPI.Web.Auth;
-using SpotifyAPI.Web.Enums;
-using SpotifyAPI.Web.Models;
 using Image = System.Drawing.Image;
 
 namespace SpotifyAPI.Example
@@ -37,7 +36,7 @@ namespace SpotifyAPI.Example
             _auth.OnResponseReceivedEvent += _auth_OnResponseReceivedEvent;
         }
 
-        void _auth_OnResponseReceivedEvent(Token token, string state)
+        private void _auth_OnResponseReceivedEvent(Token token, string state)
         {
             _auth.StopHttpServer();
 
@@ -77,7 +76,7 @@ namespace SpotifyAPI.Example
             _savedTracks.ForEach(track => savedTracksListView.Items.Add(new ListViewItem()
             {
                 Text = track.Name,
-                SubItems = {string.Join(",", track.Artists.Select(source => source.Name)), track.Album.Name}
+                SubItems = { string.Join(",", track.Artists.Select(source => source.Name)), track.Album.Name }
             }));
 
             _playlists = GetPlaylists();

SpotifyAPI.Tests/Properties/AssemblyInfo.cs

@@ -1,5 +1,4 @@
 using System.Reflection;
-using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
 // Allgemeine Informationen über eine Assembly werden über die folgenden

SpotifyAPI.Tests/TestClass.cs

@@ -1,11 +1,11 @@
-using System;
+using Moq;
-using System.IO;
-using System.Linq;
-using Moq;
 using Newtonsoft.Json;
 using NUnit.Framework;
 using SpotifyAPI.Web;
 using SpotifyAPI.Web.Models;
+using System;
+using System.IO;
+using System.Linq;
 
 namespace SpotifyAPI.Tests
 {

SpotifyAPI/Local/SpotifyLocalAPI.cs

@@ -162,10 +162,12 @@ namespace SpotifyAPI.Local
         public void Mute()
         {
             //Windows < Windows Vista Check
-            Contract.Requires(Environment.OSVersion.Version.Major >= 6);
+            if (Environment.OSVersion.Version.Major < 6)
+                throw new NotSupportedException("This feature is only available on Windows 7 or newer");
             //Windows Vista Check
             if (Environment.OSVersion.Version.Major == 6)
-                Contract.Requires(Environment.OSVersion.Version.Minor != 0);
+                if(Environment.OSVersion.Version.Minor == 0)
+                    throw new NotSupportedException("This feature is only available on Windows 7 or newer");
             VolumeMixerControl.MuteSpotify(true);
         }
 
@@ -175,10 +177,12 @@ namespace SpotifyAPI.Local
         public void UnMute()
         {
             //Windows < Windows Vista Check
-            Contract.Requires(Environment.OSVersion.Version.Major >= 6);
+            if (Environment.OSVersion.Version.Major < 6)
+                throw new NotSupportedException("This feature is only available on Windows 7 or newer");
             //Windows Vista Check
             if (Environment.OSVersion.Version.Major == 6)
-                Contract.Requires(Environment.OSVersion.Version.Minor != 0);
+                if (Environment.OSVersion.Version.Minor == 0)
+                    throw new NotSupportedException("This feature is only available on Windows 7 or newer");
             VolumeMixerControl.MuteSpotify(false);
         }
 
@@ -186,13 +190,15 @@ namespace SpotifyAPI.Local
         /// Checks whether Spotify is muted in the Volume Mixer control (required Windows 7 or newer)
         /// </summary>
         /// <returns>Null if an error occured, otherwise the muted state</returns>
-        public bool? IsSpotifyMuted()
+        public bool IsSpotifyMuted()
         {
             //Windows < Windows Vista Check
-            Contract.Requires(Environment.OSVersion.Version.Major >= 6);
+            if (Environment.OSVersion.Version.Major < 6)
+                throw new NotSupportedException("This feature is only available on Windows 7 or newer");
             //Windows Vista Check
             if (Environment.OSVersion.Version.Major == 6)
-                Contract.Requires(Environment.OSVersion.Version.Minor != 0);
+                if (Environment.OSVersion.Version.Minor == 0)
+                    throw new NotSupportedException("This feature is only available on Windows 7 or newer");
             return VolumeMixerControl.IsSpotifyMuted();
         }
 
@@ -202,12 +208,15 @@ namespace SpotifyAPI.Local
         /// <param name="volume">A value between 0 and 100</param>
         public void SetSpotifyVolume(float volume = 100)
         {
-            Contract.Requires(0 <= volume && volume <= 100);
             //Windows < Windows Vista Check
-            Contract.Requires(Environment.OSVersion.Version.Major >= 6);
+            if (Environment.OSVersion.Version.Major < 6)
+                throw new NotSupportedException("This feature is only available on Windows 7 or newer");
             //Windows Vista Check
             if (Environment.OSVersion.Version.Major == 6)
-                Contract.Requires(Environment.OSVersion.Version.Minor != 0);
+                if (Environment.OSVersion.Version.Minor == 0)
+                    throw new NotSupportedException("This feature is only available on Windows 7 or newer");
+            if (volume < 0 || volume > 100)
+                throw new ArgumentOutOfRangeException("Volume parameter has to be a value between 0 and 100");
             VolumeMixerControl.SetSpotifyVolume(volume);
         }
 
@@ -215,13 +224,15 @@ namespace SpotifyAPI.Local
         /// Return the Volume Mixer volume of Spotify (requires Windows 7 or newer)
         /// </summary>
         /// <returns>Null if an error occured, otherwise a float between 0 and 100</returns>
-        public float? GetSpotifyVolume()
+        public float GetSpotifyVolume()
         {
             //Windows < Windows Vista Check
-            Contract.Requires(Environment.OSVersion.Version.Major >= 6);
+            if (Environment.OSVersion.Version.Major < 6)
+                throw new NotSupportedException("This feature is only available on Windows 7 or newer");
             //Windows Vista Check
             if (Environment.OSVersion.Version.Major == 6)
-                Contract.Requires(Environment.OSVersion.Version.Minor != 0);
+                if (Environment.OSVersion.Version.Minor == 0)
+                    throw new NotSupportedException("This feature is only available on Windows 7 or newer");
             return VolumeMixerControl.GetSpotifyVolume();
         }
 

SpotifyAPI/Local/VolumeMixerControl.cs

@@ -8,17 +8,20 @@ namespace SpotifyAPI.Local
     {
         private const String SPOTIFY_PROCESS_NAME = "spotify";
 
-        internal static float? GetSpotifyVolume()
+        internal static float GetSpotifyVolume()
         {
             Process[] p = Process.GetProcessesByName(SPOTIFY_PROCESS_NAME);
             if (p.Length == 0)
-                return null;
+                throw new Exception("Spotify process is not running or was not found!");
 
             int pid = p[0].Id;
 
             ISimpleAudioVolume volume = GetVolumeObject(pid);
             if (volume == null)
-                return null;
+            {
+                Marshal.ReleaseComObject(volume);
+                throw new COMException("Volume object creation failed");
+            }
 
             float level;
             volume.GetMasterVolume(out level);
@@ -26,17 +29,20 @@ namespace SpotifyAPI.Local
             return level * 100;
         }
 
-        internal static bool? IsSpotifyMuted()
+        internal static bool IsSpotifyMuted()
         {
             Process[] p = Process.GetProcessesByName(SPOTIFY_PROCESS_NAME);
             if (p.Length == 0)
-                return null;
+                throw new Exception("Spotify process is not running or was not found!");
 
             int pid = p[0].Id;
 
             ISimpleAudioVolume volume = GetVolumeObject(pid);
             if (volume == null)
-                return null;
+            {
+                Marshal.ReleaseComObject(volume);
+                throw new COMException("Volume object creation failed");
+            }
 
             bool mute;
             volume.GetMute(out mute);
@@ -48,13 +54,16 @@ namespace SpotifyAPI.Local
         {
             Process[] p = Process.GetProcessesByName(SPOTIFY_PROCESS_NAME);
             if (p.Length == 0)
-                return;
+                throw new Exception("Spotify process is not running or was not found!");
 
             int pid = p[0].Id;
 
             ISimpleAudioVolume volume = GetVolumeObject(pid);
             if (volume == null)
-                return;
+            {
+                Marshal.ReleaseComObject(volume);
+                throw new COMException("Volume object creation failed");
+            }
 
             Guid guid = Guid.Empty;
             volume.SetMasterVolume(level / 100, ref guid);
@@ -65,13 +74,16 @@ namespace SpotifyAPI.Local
         {
             Process[] p = Process.GetProcessesByName(SPOTIFY_PROCESS_NAME);
             if (p.Length == 0)
-                return;
+                throw new Exception("Spotify process is not running or was not found!");
 
             int pid = p[0].Id;
 
             ISimpleAudioVolume volume = GetVolumeObject(pid);
             if (volume == null)
-                return;
+            {
+                Marshal.ReleaseComObject(volume);
+                throw new COMException("Volume object creation failed");
+            }
 
             Guid guid = Guid.Empty;
             volume.SetMute(mute, ref guid);
@@ -125,6 +137,7 @@ namespace SpotifyAPI.Local
         [Guid("BCDE0395-E52F-467C-8E3D-C4579291692E")]
         private class MMDeviceEnumerator
         {
+
         }
 
         private enum EDataFlow