在一个linq查询中使用了平均值聚合函数Average,结果报错 System.InvalidOperationException Sequence contains no elements (序列不包含任何元素) 也就是说,使用某些linq的函数时,如果值不存在是会报错的,比如: First()Single()FirstAsync()SingleAsync()Last()LastAsync()Max()Min()Average() 等, 解决方案: 使用空...
When you start playing with LINQ queries over sequences of elements (e.g. getting min / max value for enumerable source) sooner or later you will come across this one -- the InvalidOperationException (“Sequence contains no elements”). The problem occurs as by default queries like IEnumerabl...
Returns the first element of the sequence that satisfies a condition or a default value if no such element is found. FirstOrDefault<TSource>(IEnumerable<TSource>) Returns the first element of a sequence, or a default value if the sequence contains no elements. ...
Returns the first element of a sequence. FirstOrDefault<TSource>(IEnumerable<TSource>, TSource) Returns the first element of a sequence, or a specified default value if the sequence contains no elements. FirstOrDefault<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>, TSource) ...
Returns the first element of the sequence that satisfies a condition or a default value if no such element is found. FirstOrDefault<TSource>(IEnumerable<TSource>) Returns the first element of a sequence, or a default value if the sequence contains no elements. ...
Returns the first element of a sequence. FirstOrDefault<TSource>(IEnumerable<TSource>, TSource) Returns the first element of a sequence, or a specified default value if the sequence contains no elements. FirstOrDefault<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>, TSource) ...
If there are no items, First and Single will throw an InvalidOperationException with the message “Sequence contains no elements.” FirstOrDefault and SingleOrDefault protect you from the exception by returning the default, which is generally a null (Nothing in VB). Additionally, if you use ...
下例示範如何建立名為AlternateElements的擴充方法,傳回集合中的每隔個項目,從第一個項目開始。 C# // Extension method for the IEnumerable<T> interface.// The method returns every other element of a sequence.publicstaticIEnumerable<T> AlternateElements<T>(thisIEnumerable<T> source) {int...
Checking if an ObservableCollection contains a specific object Checking if command line arguments are empty. checking if elements with values exists in xml Checking overlaps on dates in collection items Chinese Character Encoding not working in C# Choose random value from array with weight Chr(13) in...
concat<S: Sequence>(other: S) -> SinqSequence<T> contains - check if the sequence contains an element contains(value: T, equality: (T, T) -> Bool) -> Bool contains<K: Equatable>(value: T, key: T -> K) -> Bool count - count the elements in the sequence func count() -> In...