2

我有一个具有 100 多个属性的对象。然后我有一个包含很多这些对象的列表。我需要计算列表中所有属性的最小值、最大值、中值和中值。

所以不要写:

Ag = _valuesForExtraCalculations.Min(c => c.Ag),
Al = _valuesForExtraCalculations.Min(c => c.Al),
Alkal = _valuesForExtraCalculations.Min(c => c.Alkal),

那 100 次,我以为我可以使用反射,所以我写道:

var Obj = new Analysis();
Type t = Obj.GetType();
PropertyInfo[] prop = t.GetProperties();
foreach (var propertyInfo in prop)
{
    propertyInfo = _valuesForExtraCalculations.Min(?????);
}

但是我不确定在 foreach 循环中要写什么,所以我可以将该属性的新最小值设置为我创建的新分析对象。

4

2 回答 2

4

据我了解您的问题,您可以使用表达式来实现:

/// <summary>
/// A class with many-many properties
/// </summary>
class MyClass
{
    public Decimal A { get; set; }
    public Decimal B { get; set; }
    public Decimal C { get; set; }
}

class PropertyHelper<T, TProperty>
{
    private readonly Func<T, TProperty> selector;
    private readonly Action<T, TProperty> setter;

    public PropertyHelper(Func<T, TProperty> selector, Action<T, TProperty> setter)
    {
        this.selector = selector;
        this.setter = setter;
    }

    public Func<T, TProperty> Selector
    {
        get { return selector; }
    }

    public Action<T, TProperty> Setter
    {
        get { return setter; }
    }
}

class AggregateHelper<T, TProperty>
{
    private readonly Dictionary<PropertyInfo, PropertyHelper<T, TProperty>> helpers;

    public AggregateHelper()
    {
        this.helpers = typeof(T)
            .GetProperties()
            .Where(p => p.PropertyType == typeof(TProperty))
            .ToDictionary(p => p, p => new PropertyHelper<T, TProperty>(MakeSelector(p), MakeSetter(p)));
    }

    private Func<T, TProperty> MakeSelector(PropertyInfo property)
    {
        var parameterExpr = Expression.Parameter(typeof(T));
        var lambda = (Expression<Func<T, TProperty>>)Expression.Lambda(
            Expression.Property(parameterExpr, property), parameterExpr);

        return lambda.Compile();
    }

    private Action<T, TProperty> MakeSetter(PropertyInfo property)
    {
        var instanceExpr = Expression.Parameter(typeof(T));
        var parameterValueExpr = Expression.Parameter(typeof(TProperty));
        var lambda = (Expression<Action<T, TProperty>>)Expression.Lambda(
            Expression.Call(instanceExpr, property.GetSetMethod(), parameterValueExpr),
            instanceExpr,
            parameterValueExpr);

        return lambda.Compile();
    }

    public IEnumerable<PropertyInfo> Properties
    {
        get { return helpers.Keys; }
    }

    public PropertyHelper<T, TProperty> this[PropertyInfo property]
    {
        get { return helpers[property]; }
    }
}

用法:

    public static void Do()
    {
        var target = new MyClass();
        var list = new List<MyClass>
        {
            new MyClass { A = 1M, B = 2M, C = 3M },
            new MyClass { A = 10M, B = 20M, C = 30M },
            new MyClass { A = 100M, B = 200M, C = 300M }
        };

        // calculate 'min' for all decimal properties
        var helper = new AggregateHelper<MyClass, Decimal>();

        foreach (var property in helper.Properties)
        {
            var propertyHelper = helper[property];

            propertyHelper.Setter(target, list.Min(propertyHelper.Selector));
        }
    }

编译的 lambda 比反射工作得更快,并且不会有装箱/拆箱。

于 2012-05-16T13:08:13.043 回答
1

您需要知道属性的确切类型。假设它是int

var Obj = new Analysis();
Type t = Obj.GetType();
PropertyInfo[] prop = t.GetProperties();
foreach (var pi in prop.Where(p => p.PropertyType == typeof(int)) 
{
    int min = _valuesForExtraCalculations.Min(c => (int)pi.GetValue(c, null));
    propertyInfo.SetValue(Obj, min, null);
}

如果您有不同的类型要计算最小值,您将无法检查类型并相应地进行切换,以便Min调用正确的重载。

我仍然不会认为这是最好或最高效的解决方案。

PropertyInfo.GetValue并且PropertyInfo.SetValue比直接字段访问慢(根据这篇文章要慢得多),而且会涉及很多拳击。您会调用PropertyInfo.GetValue(countOfObjects * countOfProperties) 次。根据项目和属性的数量,这可能会引起关注。

于 2012-05-16T09:31:33.230 回答