c# - 计算对象的变更集

Question

我正在编写一个 Windows 应用商店应用程序，它从服务器接收一个对象(我创建的自定义类型)，让用户编辑该对象，然后将“变更集”提交回服务器。这个变更集只是一个与接收到的对象类型相同的对象，除了用户编辑的字段外，每个字段都设置为空。然后这些字段包含用户的编辑，如下所示:

Original Case:
    Description: "Cracked exhaust pipe"
    Status: "Open"
    Customer: ""
    Mileage: 10000

Edited Case:
    Description: ""
    Status "Open"
    Customer: "Example inc."
    Mileage: 10000

Case changeset:
    Description: ""
    Status: null
    Customer: "Example inc."
    Mileage: null

When the app first downloads the object from the server I make a copy of it for later comparison. The user then makes changes to one of the objects and when the user submits his changes, a changeset of these two objects is calculated with a generic method CalculateChangeSet. It goes through every property of the two objects and compares them for equality:

public static T CalculateChangeSet<T>(T oldObject, T newObject) where T : new()
{
    T changeSet = (T)Activator.CreateInstance(oldObject.GetType());

    foreach (PropertyInfo property in oldObject.GetType().GetRuntimeProperties())
    {
        var oldValue = property.GetValue(oldObject);
        var newValue = newObject.GetType().GetRuntimeProperty(property.Name).GetValue(newObject);
        if (oldValue != null && newValue != null)
        {
            if (oldValue is IList)
            {
                Type listType = oldValue.GetType().GetRuntimeProperty("Item").PropertyType;

                IList<listType> oldList = (IList<listType>)oldValue; //Visual studio complains about
                IList<listType> newList = (IList<listType>)newValue; //listType not being found

                if (!oldList.SequenceEqual(newList))
                {
                    changeSet.GetType().GetRuntimeProperty(property.Name).SetValue(changeSet, newValue, null);
                }
            }
            else
            {
                if (!oldValue.Equals(newValue))
                {
                    changeSet.GetType().GetRuntimeProperty(property.Name).SetValue(changeSet, CalculateChangeSet(oldValue, newValue));
                }
            }
        }
        else
        {
            changeSet.GetType().GetRuntimeProperty(property.Name).SetValue(changeSet, newValue);
        }
    }

    return changeSet;
}

该方法适用于我遇到的每个属性，但列表除外，因此我创建了 if 子句来处理列表。自 list1.Equals(list2)不比较列表中的项目，我们需要转换 oldValue和 newValue至 List<T>能够使用 list.SequenceEqual() .

为什么我会收到一条错误消息 The type or namespace name 'listType' could not be found (are you missing a using directive or an assembly reference?)当我尝试使用它来创建新列表时？如果有更好的方法来解决这个问题，我愿意接受建议..

Answer 1

试试这个:

IList oldList = (IList)oldValue; //Visual studio complains about
IList newList = (IList)newValue; //listType not being found

if (!NonGenericSequenceEqual(oldList, newList))
{
    changeSet.GetType().GetRuntimeProperty(property.Name).SetValue(changeSet, newValue, null);
}

public static bool NonGenericSequenceEqual(IList a, IList b)
{
    if (ReferenceEquals(a, b))
    {
        return true;
    }
    else if (a == null || b == null)
    {
        return false;
    }
    else
    {
        int count = a.Count;

        if (count != b.Count)
        {
            return false;
        }
        else
        {
            for (int i = 0; i < count; i++)
            {
                if (!Object.Equals(a[i], b[i]))
                {
                    return false;
                }
            }

            return true;
        }
    }
}

弱代码是'Object.Equals(a[i], b[i])'

通过反射的另一种变体:

if (!(bool)typeof(System.Linq.Enumerable).GetMethod("SequenceEqual").MakeGenericMethod(oldValue.GetType().GetRuntimeProperty("Item").PropertyType).Invoke(null, new object[] { oldObject, newObject }))
{
    changeSet.GetType().GetRuntimeProperty(property.Name).SetValue(changeSet, newValue, null);
}