这个错误,在使用List<T>的First函数遇到. Sequence contains no elements? From "Fixing LINQ Error: Sequence contains no elements": When you get the LINQ error "Sequence contains no elements", this is usually because you are using the First() or…

一.在.Net Core中使用Ef的聚合函数报错: 类似函数: 1,使用FirstOrDefault() 来代替 First() 2.使用SingleOrDefault 来代替 Single 3.使用 ElementAtOrDefault 来代替 .ElementAt 4.如果是在Average, Sum等中报错 错误如下: Sequence contains no elements 二.在.Net Core的 内存列表 Linq  聚合函数解决方案 var items = new int[]…

foreach (var keyCode in unexpectedKeyCodesDetected) { string unexpected = expectedCapturedKeyCodes.Where(key => key == keyCode).First(); } 空集合时,从First()处 Throw the exceptoins. 修改:  First() => FirstOrDefault(),然后对返回String做null判断.…

1.错误意思: 出现错误的原因是:你要从一个null中取的数据. 2.错误的处理 1,使用FirstOrDefault() 来代替 First() 2.使用SingleOrDefault 来代替 Single 3.使用 ElementAtOrDefault 来代替 .ElementAt 4.如果是在Average, Sum等中报错 var items = new int[] {1, 2, 3, 4, 5}; Double avg = items.Average(); 替换: Double avg…

B. Hungry Sequence time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output Iahub and Iahubina went to a date at a luxury restaurant. Everything went fine until paying for the food. Instead of money…

Lemma 21.2 (The sequence lemma) Let \(X\) be a topological space; let \(A \subset X\). If there is a sequence of points of \(A\) converging to \(x\), then \(x \in \bar{A}\); the converse holds if \(X\) is metrizable. Proof a) Sequence convergence \(\…

题目链接:https://cn.vjudge.net/problem/CodeForces-894C In a dream Marco met an elderly man with a pair of black glasses. The man told him the key to immortality and then disappeared with the wind of time. When he woke up, he only remembered that the key…

B. Hungry Sequence time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output Iahub and Iahubina went to a date at a luxury restaurant. Everything went fine until paying for the food. Instead of money…

C. Marco and GCD Sequence time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output In a dream Marco met an elderly man with a pair of black glasses. The man told him the key to immortality and then…

. Hungry Sequence time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output Iahub and Iahubina went to a date at a luxury restaurant. Everything went fine until paying for the food. Instead of money,…