如何将谓词作为参数C＃传递 [英] How to pass a predicate as parameter c#

问题描述

如何在不传递谓词的情况下将谓词传递给方法，又如何使它起作用？我想也许是这样，但这似乎不正确。

How can I pass a predicate into a method but also have it work if no predicate is passed? I thought maybe something like this, but it doesn't seem to be correct.

private bool NoFilter() { return true; }

private List<thing> GetItems(Predicate<thing> filter = new Predicate<thing>(NoFilter))
{
    return rawList.Where(filter).ToList();
}

推荐答案

private List<thing> GetItems(Func<thing, bool> filter = null)
{
    return rawList.Where(filter ?? (s => true)).ToList();
}

在此表达式中 s => true 是后备过滤器，如果参数 filter 为空，则将对其求值。它只获取列表的每个条目（如 s ）并返回 true 。

In this expression s => true is the fallback filter which is evaluated if the argument filter is null. It just takes each entry of the list (as s) and returns true.

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