表达式.转换:类型为'System.Int64'不能转换为类型'System.Int32'

昨天我在这里问了一个关于从匿名对象读取属性并将其写入类的私有字段的问题。问题解决了。这是一个短篇故事:

我有一些json格式的数据。我将它们反序列化为ExpandoObject，并将它们作为IDictionary<string, object>传递给方法。它工作良好，除了Int32性质。似乎它们变成了Int64，在哪里?我不知道。

下面是方法:

    private Func<IDictionary<string, object>, dynamic> MakeCreator(
        Type type, Expression ctor,
        IEnumerable<PropertyToFieldMapper> maps) {
        var list = new List<Expression>();
        var vList = new List<ParameterExpression>();
        // creating new target
        var targetVariable = Expression.Variable(type, "targetVariable");
        vList.Add(targetVariable);
        list.Add(Expression.Assign(targetVariable, Expression.Convert(ctor, type)));
        // accessing source
        var sourceType = typeof(IDictionary<string, object>);
        var sourceParameter = Expression.Parameter(sourceType, "sourceParameter");
        // calling source ContainsKey(string) method
        var containsKeyMethodInfo = sourceType.GetMethod("ContainsKey", new[] { typeof(string) });
        var accessSourceIndexerProp = sourceType.GetProperty("Item");
        var accessSourceIndexerInfo = accessSourceIndexerProp.GetGetMethod();
        // itrate over writers and add their Call to block
        var containsKeyMethodArgument = Expression.Variable(typeof(string), "containsKeyMethodArgument");
        vList.Add(containsKeyMethodArgument);
        foreach (var map in maps) {
            list.Add(Expression.Assign(containsKeyMethodArgument, Expression.Constant(map.Property.Name)));
            var containsKeyMethodCall = Expression.Call(sourceParameter, containsKeyMethodInfo,
                                                        new Expression[] { containsKeyMethodArgument });
            // creating writer
            var sourceValue = Expression.Call(sourceParameter, accessSourceIndexerInfo,
                                              new Expression[] { containsKeyMethodArgument });
            var setterInfo = map.Field.GetType().GetMethod("SetValue", new[] { typeof(object), typeof(object) });
            var setterCall = Expression.Call(Expression.Constant(map.Field), setterInfo,
                new Expression[] {
                                     Expression.Convert(targetVariable, typeof(object)),
                                     Expression.Convert(sourceValue, typeof(object))
                                 });
            Console.WriteLine(Expression.Lambda(setterCall));
            list.Add(Expression.IfThen(containsKeyMethodCall, setterCall));
        }
        list.Add(targetVariable);
        var block = Expression.Block(vList, list);
        var lambda = Expression.Lambda<Func<IDictionary<string, object>, dynamic>>(
            block, new[] { sourceParameter }
            );
        return lambda.Compile();
    }

如果我们有这个

public class Person {
    public int Age { get; set; }
    public string Name { get; set; }
}

类，并使用该对象

var data = new { Name = "Amiry", Age = 20 };

使用上面的方法初始化Person的实例，出现这个错误:

System类型的对象。Int64'无法转换为'System.Int32'类型。

但是如果我们改变Age属性为:

public long Age { get; set; }

一切看起来都很好，方法也很有效。我完全不明白为什么会这样。你知道吗?

public class JsonIntegerConverter : JsonConverter {
    public override bool CanConvert(Type objectType) {
        return objectType == typeof(IDictionary<string, object>);
    }
    public override bool CanWrite {
        get { return false; }
    }
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) {
        var result = new Dictionary<string, object>();
        reader.Read();
        while (reader.TokenType == JsonToken.PropertyName) {
            var propertyName = (string)reader.Value;
            reader.Read();
            object value;
            if (reader.TokenType == JsonToken.Integer) {
                var temp = Convert.ToInt64(reader.Value);
                if (temp <= Byte.MaxValue && temp >= Byte.MinValue)
                    value = Convert.ToByte(reader.Value);
                else if (temp >= Int16.MinValue && temp <= Int16.MaxValue)
                    value = Convert.ToInt16(reader.Value);
                else if (temp >= Int32.MinValue && temp <= Int32.MaxValue)
                    value = Convert.ToInt32(reader.Value);
                else
                    value = temp;
            } else
                value = serializer.Deserialize(reader);
            result.Add(propertyName, value);
            reader.Read();
        }
        return result;
    }
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) {
        throw new NotSupportedException();
    }
}