Question

我有此代码：

         switch (Settings.cvm)
         {
            case CVM.IncludeHidden:
                return new SelectedPhrases()
                {
                    ps = ps,
                    psNoa = psNoa
                };
            case CVM.ExcludeHidden:
                return new SelectedPhrases()
                {
                    ps = ps.Where(x => x.Hidden == false).ToList(),
                    psNoa = psNoa.Where(x => x.Hidden == false).ToList()
                };
            case CVM.Hidden:
                return new SelectedPhrases()
                {
                    ps = ps.Where(x => x.Hidden == true).ToList(),
                    psNoa = psNoa.Where(x => x.Hidden == true).ToList()
                };
            case CVM.Favorites:
                return new SelectedPhrases()
                {
                    ps = ps.Where(x => x.Favorite == true).ToList(),
                    psNoa = psNoa.Where(x => x.Favorite == true).ToList()
                };
            default:
                return null;

        }

有什么方法可以让开关只返回where子句，而不是从开关内部返回：

x => x.Hidden == false

然后在开关之后将where子句添加到变量ps和psNoa中？

Answer 1

您可以将委派Func用于where子句。然后将委托放入Where（）方法。

void Main()
{
    var persons = new []
    {
        new Person { Id = 1, Name = "Alice", Active = true },
        new Person { Id = 2, Name = "Bob", Active = false },
        new Person { Id = 3, Name = "Charlie", Active = true },
    };

    Func<Person, bool> whereClause;

    var isActive = true; // change the value here
    if (isActive)
        whereClause = x => x.Active == true;
    else
        whereClause = x => x.Active == false;

    var query = persons.Where(whereClause);
    query.Dump();   
}

class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
    public bool Active { get; set; }
}

LinqPad中的结果：

Answer 2

是的，确实可以

在开关中做

case zzz:
    ps = ps.Where(xxxxx).ToList();
    psnoa = psnoa.Where(yyyy).ToList();
    break;
....

然后切换。

            return new SelectedPhrases()
            {
                ps.ToList(),
                psNoa.ToList()
            };

关键是您可以逐步进行LINQ操作的管道。注意-最好将所有内容都保留为IEnuemrable而不是List。这样会将评估推迟到最后

有没有一种方法可以将包含LINQ where子句的字符串添加到列表中？

2 个答案: