XML编译错误

Question

我从C＃和XNA开始。我正在尝试使用一个小库来使用基于组件的设计。

当我尝试使用XML在游戏中制作实体时出现问题。编译器发送该错误：

Error   1   Building content threw NullReferenceException: Object reference not set to an instance of an object.
   at ReflectionEmitUtils(Object , Object )
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.ReflectiveSerializerMemberHelper.DeserializeRegularObject(IntermediateReader input, Object parentInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.ReflectiveSerializerMemberHelper.Deserialize(IntermediateReader input, Object parentInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.ReflectiveSerializer.Deserialize(IntermediateReader input, ContentSerializerAttribute format, Object existingInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.IntermediateReader.ReadRawObjectInternal[T](ContentSerializerAttribute format, ContentTypeSerializer typeSerializer, Object existingInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.IntermediateReader.ReadObjectInternal[T](ContentSerializerAttribute format, ContentTypeSerializer typeSerializer, Object existingInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.IntermediateReader.ReadObject[T](ContentSerializerAttribute format, ContentTypeSerializer typeSerializer)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.DictionarySerializer`2.Deserialize(IntermediateReader input, ContentSerializerAttribute format, Dictionary`2 existingInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.ContentTypeSerializer`1.Deserialize(IntermediateReader input, ContentSerializerAttribute format, Object existingInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.IntermediateReader.ReadRawObjectInternal[T](ContentSerializerAttribute format, ContentTypeSerializer typeSerializer, Object existingInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.IntermediateReader.ReadObjectInternal[T](ContentSerializerAttribute format, ContentTypeSerializer typeSerializer, Object existingInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.ReflectiveSerializerMemberHelper.DeserializeRegularObject(IntermediateReader input, Object parentInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.ReflectiveSerializerMemberHelper.Deserialize(IntermediateReader input, Object parentInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.ReflectiveSerializer.Deserialize(IntermediateReader input, ContentSerializerAttribute format, Object existingInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.IntermediateReader.ReadRawObjectInternal[T](ContentSerializerAttribute format, ContentTypeSerializer typeSerializer, Object existingInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.IntermediateReader.ReadObjectInternal[T](ContentSerializerAttribute format, ContentTypeSerializer typeSerializer, Object existingInstance)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.IntermediateReader.ReadObject[T](ContentSerializerAttribute format)
   at Microsoft.Xna.Framework.Content.Pipeline.Serialization.Intermediate.IntermediateSerializer.Deserialize[T](XmlReader input, String referenceRelocationPath)
   at Microsoft.Xna.Framework.Content.Pipeline.XmlImporter.Import(String filename, ContentImporterContext context)
   at Microsoft.Xna.Framework.Content.Pipeline.ContentImporter`1.Microsoft.Xna.Framework.Content.Pipeline.IContentImporter.Import(String filename, ContentImporterContext context)
   at Microsoft.Xna.Framework.Content.Pipeline.BuildCoordinator.ImportAssetDirectly(BuildItem item, String importerName)
   at Microsoft.Xna.Framework.Content.Pipeline.BuildCoordinator.ImportAsset(BuildItem item)
   at Microsoft.Xna.Framework.Content.Pipeline.BuildCoordinator.BuildAssetWorker(BuildItem item)
   at Microsoft.Xna.Framework.Content.Pipeline.BuildCoordinator.BuildAsset(BuildItem item)
   at Microsoft.Xna.Framework.Content.Pipeline.BuildCoordinator.RunTheBuild()
   at Microsoft.Xna.Framework.Content.Pipeline.Tasks.BuildContent.RemoteProxy.RunTheBuild(BuildCoordinatorSettings settings, TimestampCache timestampCache, ITaskItem[] sourceAssets, String[]& outputContent, String[]& rebuiltContent, String[]& intermediates, Dictionary`2& dependencyTimestamps, KeyValuePair`2[]& warnings)   c:\Users\Agustin\Documents\Visual Studio 2010\Projects\LibraryTest\LibraryTest\LibraryTestContent\XML\Circle.xml    LibraryTest

我知道xml文件存在问题，因为如果我将“Build action”属性设置为None，则此错误消失。 xml：

<?xml version="1.0" encoding="utf-8" ?>
<XnaContent xmlns:Framework="Microsoft.Xna.Framework"
            xmlns:Graphics="Microsoft.Xna.Graphics"
            xmlns:CAEL="ComponentsAndEntitiesLibrary"
            xmlns:Components="ComponentsAndEntitiesLibrary.BasicComponents">
  <Asset Type="CAEL:Entity">
    <HeavyComponents>
      <Item>
        <Key>Sprite</Key>
        <Value Type="Components:SpriteSheet">
          <SpriteFile>Images/threerings</SpriteFile>
          <XSheet>0</XSheet>
          <YSheet>0</YSheet>
          <HeightSheet>8</HeightSheet>
          <WidthSheet>6</WidthSheet>
        </Value>
      </Item>
    </HeavyComponents>
    <LightComponents>
      <Item>
        <Key>Color</Key>
        <Value Type="Components:Color">
          <ColorValue Null="true" />
        </Value>
      </Item>
      <Item>
        <Key>Position</Key>
        <Value Type="Components:Position">
          <X>0</X>
          <Y>0</Y>
        </Value>
      </Item>
      <Item>
        <Key>Metrics</Key>
        <Value Type="Components:Metrics">
          <Height>75</Height>
          <Width>75</Width>
        </Value>
      </Item>
    </LightComponents>
    <Id>Ring</Id>
  </Asset>
</XnaContent>

这就是我使用的课程：

Entity.cs

namespace ComponentsAndEntitiesLibrary
{
    public class Entity : HeavyComponent
    {
        private Dictionary<string, Component> heavyComponents;
        private Dictionary<string, Component> lightComponents;

        private string id;

        public Entity(string id)
            : base(id)
        {
            this.id = id;
            heavyComponents = new Dictionary<string, Component>();
            lightComponents = new Dictionary<string, Component>();
        }

        public Entity()
            : base("")
        {
            this.id = "";
            heavyComponents = new Dictionary<string, Component>();
            lightComponents = new Dictionary<string, Component>();
        }

        public Dictionary<string, Component> HeavyComponents
        {
            get { return heavyComponents; }
            set
            {
                heavyComponents = HeavyComponents;
                foreach (Component comp in HeavyComponents.Values) addComponent(comp);
            }
        }

        public Dictionary<string, Component> LightComponents
        {
            get { return lightComponents; }
            set
            {
                lightComponents = LightComponents;
                foreach (Component comp in LightComponents.Values) addComponent(comp);
            }
        }

        public string Id
        {
            get { return id; }
            set { id = Id; }
        }
        blablablablablablablabla
    }
}

颜色

namespace ComponentsAndEntitiesLibrary
{
    namespace BasicComponents
    {
        public class Color : LightweightComponent
        {
            private const string name = "Color";
            private Microsoft.Xna.Framework.Color color;

            public Color()
                : base(name)
            {
                color = Microsoft.Xna.Framework.Color.White;
            }

            public Color(Microsoft.Xna.Framework.Color color)
                : base(name)
            {
                this.color = color;
            }

            public Microsoft.Xna.Framework.Color ColorValue
            {
                get { return color; }
                set { color = ColorValue; }
            }
        }
    }
}

Position.cs：

namespace ComponentsAndEntitiesLibrary
{
    namespace BasicComponents
    {
        public class Position : LightweightComponent
        {
            private const string name = "Position";
            private float x;
            private float y;
            private float z;

            public Position()
                : base(name)
            {
                x = y = z = 0;
            }

            public Position(float x, float y)
                : base(name)
            {
                this.x = x;
                this.y = y;
                z = 0;
            }

            public Position(float x, float y, float z)
                : base(name)
            {
                this.x = x;
                this.y = y;
                this.z = z;
            }

            public float X
            {
                get { return x; }
                set { this.x = X; }
            }

            public float Y
            {
                get { return y; }
                set { this.y = Y; }
            }

            public float Z
            {
                get { return z; }
                set { this.z = Z; }
            }

            blablablablablablablablabla
        }
    }
}

Metrics.cs

namespace ComponentsAndEntitiesLibrary
{
    namespace BasicComponents
    {
        public class Metrics : LightweightComponent
        {
            private const string name = "Metrics";
            private float height;
            private float width;

            public Metrics()
                : base(name)
            {
                height = width = 0;
            }

            public Metrics(float height, float width)
                : base(name)
            {
                this.height = height;
                this.width = width;
            }

            public float Height
            {
                get { return height; }
                set { height = Height; }
            }

            public float Width 
            {
                get { return width; }
                set { width = Width; }
            }
        }
    }
}

SpriteSheet.cs：

namespace ComponentsAndEntitiesLibrary
{
    namespace BasicComponents
    {
        public class SpriteSheet : Sprite
        {
            private int xSheet;
            private int ySheet;
            private int heightSheet;
            private int widthSheet;
            private Metrics metrics;

            public SpriteSheet()
                : base()
            {
                xSheet = 0;
                ySheet = 0;
            }

            public SpriteSheet(string spriteFile)
                : base(spriteFile)
            {
                xSheet = 0;
                ySheet = 0;
            }

            public int XSheet
            {
                get { return xSheet; }
                set { xSheet = XSheet; }
            }

            public int YSheet
            {
                get { return ySheet; }
                set { ySheet = YSheet; }
            }

            public int HeightSheet
            {
                get { return heightSheet; }
                set { heightSheet = HeightSheet; }
            }

            public int WidthSheet
            {
                get { return widthSheet; }
                set { widthSheet = WidthSheet; }
            }

            blablablablablablabla
        }
    }
}

可能是一个愚蠢的问题，但我没有经验，我看不到它。

感谢。

编辑：

解决。更改Color类以使属性Color可选，并从xml中删除该错误消失。然而，我不知道为什么。