Question

我的方法接收所有DataTables参数以按列单击对表进行排序。我从每个页面列表的控制器调用此方法。我正在寻找一种更好的方法，像所有类型的通用方法一样：字符串， int ，十进制， double ， bool （可空或不）。但是我无法找到它。

我目前的代码：

public List<T> OrderingList<T>(List<T> list, DataTablesParam model)
{
    var iColumn = model.Order.FirstOrDefault().Column;
    var property = typeof(T).GetProperty(model.Columns.ToArray()[iColumn].Data);
    var param = Expression.Parameter(typeof(T));
    var final = Expression.Property(param, property);

    var isDirAsc = model.Order.FirstOrDefault().Dir.Equals("asc");

    if (property.PropertyType == typeof(string))
    {
        var lambda = Expression.Lambda<Func<T, string>>(final, param).Compile();
        return isDirAsc ? list.OrderBy(lambda).ToList() : list.OrderByDescending(lambda).ToList();
    }
    else if (property.PropertyType == typeof(int))
    {
        var lambda = Expression.Lambda<Func<T, int>>(final, param).Compile();
        return isDirAsc ? list.OrderBy(lambda).ToList() : list.OrderByDescending(lambda).ToList();
    }
    else if (property.PropertyType == typeof(bool))
    {
        var lambda = Expression.Lambda<Func<T, bool>>(final, param).Compile();
        return isDirAsc ? list.OrderBy(lambda).ToList() : list.OrderByDescending(lambda).ToList();
    }
    else if (property.PropertyType == typeof(decimal))
    {
        var lambda = Expression.Lambda<Func<T, decimal>>(final, param).Compile();
        return isDirAsc ? list.OrderBy(lambda).ToList() : list.OrderByDescending(lambda).ToList();
    }
    else if (property.PropertyType == typeof(double))
    {
        var lambda = Expression.Lambda<Func<T, double>>(final, param).Compile();
        return isDirAsc ? list.OrderBy(lambda).ToList() : list.OrderByDescending(lambda).ToList();
    }

    return list;
}

我想做这样的事情:(但这段代码不起作用）

public List<T> OrderingList<T>(List<T> list, DataTablesParam model)
{
    var iColumn = model.Order.FirstOrDefault().Column;
    var property = typeof(T).GetProperty(model.Columns.ToArray()[iColumn].Data);
    var param = Expression.Parameter(typeof(T));
    var final = Expression.Property(param, property);

    var isDirAsc = model.Order.FirstOrDefault().Dir.Equals("asc");

    var lambda = Expression.Lambda<Func<T, dynamic>>(final, param).Compile();
    return isDirAsc ? list.OrderBy(lambda).ToList() : list.OrderByDescending(lambda).ToList();
}

Answer 1

您只需使用反射调用Enumerable.OrderBy方法即可。这样，您不必在编译时知道类型。为此，您只需要获取方法，并使用属性的类型创建泛型方法：

private IEnumerable<T> Sort<T> (List<T> list, string propertyName)
{
    MethodInfo orderByMethod = typeof(Enumerable).GetMethods().First(mi => mi.Name == "OrderBy" && mi.GetParameters().Length == 2);

    PropertyInfo pi = typeof(T).GetProperty(propertyName);
    MethodInfo orderBy = orderByMethod.MakeGenericMethod(typeof(T), pi.PropertyType);

    ParameterExpression param = Expression.Parameter(typeof(T));
    Delegate accessor = Expression.Lambda(Expression.Property(param, pi), param).Compile();
    return (IEnumerable<T>)orderBy.Invoke(null, new object[] { lst, accessor });
}

请注意，我抽象出了有关模型的内容，以保持此方法的通用性。它基本上可以通过指定属性名称按列表中的任何属性进行排序。您的原始方法将如下所示：

public List<T> OrderingList<T>(List<T> list, DataTablesParam model)
{
    var iColumn = model.Order.FirstOrDefault().Column;
    string propertyName = model.Columns.ToArray()[iColumn].Data;

    return Sort(list, propertyName).ToList();
}

Answer 2

Beyond just not being very generic, your solution also requires a lot of extra memory because you're copying the list with LINQ. You can avoid this using List.Sort.

I would do:

static void SortBy<T>(List<T> list, MemberInfo member, bool desc)
{
    Comparison<T> cmp = BuildComparer<T>(member, desc);
    list.Sort(cmp);
}

static Comparison<T> BuildComparer<T>(MemberInfo member, bool desc)
{
    var left = Expression.Parameter(typeof(T));
    var right = Expression.Parameter(typeof(T));

    Expression cmp = Expression.Call(
        Expression.MakeMemberAccess(desc ? right : left, member),
        "CompareTo",
        Type.EmptyTypes,
        Expression.MakeMemberAccess(desc ? left : right, member));

    return Expression.Lambda<Comparison<T>>(cmp, left, right).Compile();
}

Answer 3

It's works fine for me: (Thanks @Poke)

https://stackoverflow.com/a/31393168/5112444

My final method:

private IEnumerable<T> Sort<T>(IEnumerable<T> list, string propertyName, bool isAsc)
{
    MethodInfo orderByMethod = typeof(Enumerable).GetMethods().First(mi => mi.Name == (isAsc ? "OrderBy" : "OrderByDescending") && mi.GetParameters().Length == 2);

    PropertyInfo pi = typeof(T).GetProperty(propertyName);
    MethodInfo orderBy = orderByMethod.MakeGenericMethod(typeof(T), pi.PropertyType);

    ParameterExpression param = Expression.Parameter(typeof(T));
    Delegate accessor = Expression.Lambda(Expression.Call(param, pi.GetGetMethod()), param).Compile();
    return (IEnumerable<T>)orderBy.Invoke(null, new object[] { list, accessor });
}

Answer 4

您建议的方法几乎可行。您需要更改两件事才能使其正常工作：

public List<T> OrderingList<T>(List<T> list, DataTablesParam model)
{
    var iColumn = model.Order.FirstOrDefault().Column;
    var property = typeof(T).GetProperty(model.Columns.ToArray()[iColumn].Data);
    var param = Expression.Parameter(typeof(T), "p");
    Expression final = Expression.Property(param, property);

    // Boxing of value types
    if (property.PropertyType.IsValueType) {
        final = Expression.MakeUnary(ExpressionType.Convert, final, typeof(object));
    }

    var isDirAsc = model.Order.FirstOrDefault().Dir.Equals("asc");

    //                                     VVVVVV
    var lambda = Expression.Lambda<Func<T, object>>(final, param).Compile();
    return isDirAsc
        ? list.OrderBy(lambda).ToList()
        : list.OrderByDescending(lambda).ToList();
}

而不是dynamic使用object，因为每种类型都是object。

如果您有值类型，则需要装箱操作，即必须将值强制转换为对象(object)i。这是通过一元转换操作完成的：

Expression final = Expression.Property(param, property);
if (property.PropertyType.IsValueType) {
    final = Expression.MakeUnary(ExpressionType.Convert, final, typeof(object));
}

另请注意，final显式声明为Expression，因为表达式类型可能会从属性更改为一元表达式。

Answer 5

我找到了一个更好的方法来做到这一点。我必须做3个步骤：

1 - 在项目中添加“Linq Dynamic”软件包：

Install-Package System.Linq.Dynamic.Library

2 - 在Class中导入包：

using System.Linq.Dynamic;

3 - 按字符串名称列出的订单列表：

list.OrderBy(stringPropertyName);                 //asc
list.OrderBy(stringPropertyName + " descending"); //des

它非常适合我。

通过任何属性对列表进行排序的更好方法

5 个答案: