Queryable.ThenByDescending 方法

定义

按降序对序列中的元素执行后续排序。

重载

ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>)

根据某个键按降序对序列中的元素执行后续排序。

ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>)

使用指定的比较器按降序对序列中的元素执行后续排序。

ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>)

根据某个键按降序对序列中的元素执行后续排序。

public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IOrderedQueryable<TSource> ^ ThenByDescending(System::Linq::IOrderedQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, TKey> ^> ^ keySelector);
public static System.Linq.IOrderedQueryable<TSource> ThenByDescending<TSource,TKey> (this System.Linq.IOrderedQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,TKey>> keySelector);
static member ThenByDescending : System.Linq.IOrderedQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, 'Key>> -> System.Linq.IOrderedQueryable<'Source>
<Extension()>
Public Function ThenByDescending(Of TSource, TKey) (source As IOrderedQueryable(Of TSource), keySelector As Expression(Of Func(Of TSource, TKey))) As IOrderedQueryable(Of TSource)

类型参数

TSource

source 的元素类型。

TKey

keySelector 表示的函数返回的键类型。

参数

source
IOrderedQueryable<TSource>

一个包含要排序的元素的 IOrderedQueryable<T>

keySelector
Expression<Func<TSource,TKey>>

用于从每个元素中提取键的函数。

返回

IOrderedQueryable<TSource>

一个 IOrderedQueryable<T>,将根据键按降序对其元素进行排序。

例外

sourcekeySelectornull

注解

此方法至少有一个类型参数,其类型 Expression<TDelegate> 参数为类型之 Func<T,TResult> 一。 For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

该方法ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>)生成一个表示调用ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>)本身为构造泛型方法的一个MethodCallExpression方法。 然后,MethodCallExpressionCreateQuery<TElement>(Expression)它将传递给由参数属性source表示Provider的方法IQueryProvider。 调用 CreateQuery<TElement>(Expression) 的结果将强制转换为类型 IOrderedQueryable<T> 并返回。

执行表示调用 ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>) 的表达式树导致的查询行为取决于参数类型的 source 实现。 预期行为是,它根据调用每个元素source获取keySelector的键执行降序的元素的source辅助排序。 保留以前建立的所有排序顺序。

适用于

ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>)

使用指定的比较器按降序对序列中的元素执行后续排序。

public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IOrderedQueryable<TSource> ^ ThenByDescending(System::Linq::IOrderedQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, TKey> ^> ^ keySelector, System::Collections::Generic::IComparer<TKey> ^ comparer);
public static System.Linq.IOrderedQueryable<TSource> ThenByDescending<TSource,TKey> (this System.Linq.IOrderedQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,TKey>> keySelector, System.Collections.Generic.IComparer<TKey> comparer);
public static System.Linq.IOrderedQueryable<TSource> ThenByDescending<TSource,TKey> (this System.Linq.IOrderedQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,TKey>> keySelector, System.Collections.Generic.IComparer<TKey>? comparer);
static member ThenByDescending : System.Linq.IOrderedQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, 'Key>> * System.Collections.Generic.IComparer<'Key> -> System.Linq.IOrderedQueryable<'Source>
<Extension()>
Public Function ThenByDescending(Of TSource, TKey) (source As IOrderedQueryable(Of TSource), keySelector As Expression(Of Func(Of TSource, TKey)), comparer As IComparer(Of TKey)) As IOrderedQueryable(Of TSource)

类型参数

TSource

source 的元素类型。

TKey

keySelector 函数返回的键的类型。

参数

source
IOrderedQueryable<TSource>

一个包含要排序的元素的 IOrderedQueryable<T>

keySelector
Expression<Func<TSource,TKey>>

用于从每个元素中提取键的函数。

comparer
IComparer<TKey>

用于比较键的 IComparer<T>

返回

IOrderedQueryable<TSource>

一个集合,其中的元素是根据某个键按降序进行排序的。

例外

sourcekeySelectorcomparernull

示例

下面的代码示例演示如何 ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) 使用自定义比较器按降序对序列中的元素执行辅助顺序。

public class CaseInsensitiveComparer : IComparer<string>
{
    public int Compare(string x, string y)
    {
        return string.Compare(x, y, true);
    }
}

public static void ThenByDescendingEx1()
{
    string[] fruits =
    { "apPLe", "baNanA", "apple", "APple", "orange", "BAnana", "ORANGE", "apPLE" };

    // Sort the strings first ascending by their length and
    // then descending using a custom case insensitive comparer.
    IEnumerable<string> query =
        fruits.AsQueryable()
        .OrderBy(fruit => fruit.Length)
        .ThenByDescending(fruit => fruit, new CaseInsensitiveComparer());

    foreach (string fruit in query)
        Console.WriteLine(fruit);
}

/*
    This code produces the following output:

    apPLe
    apple
    APple
    apPLE
    orange
    ORANGE
    baNanA
    BAnana
*/
Class CaseInsensitiveComparer
    Implements IComparer(Of String)

    Function Compare(ByVal x As String, ByVal y As String) As Integer _
        Implements IComparer(Of String).Compare

        ' Compare values and ignore case.
        Return String.Compare(x, y, True)
    End Function
End Class

Sub ThenByDescendingEx1()
    Dim fruits() As String = _
        {"apPLe", "baNanA", "apple", "APple", "orange", "BAnana", "ORANGE", "apPLE"}

    ' Sort the strings first ascending by their length and 
    ' then descending by using a custom case insensitive comparer.
    Dim query = fruits.AsQueryable() _
        .OrderBy(Function(fruit) fruit.Length) _
        .ThenByDescending(Function(fruit) fruit, New CaseInsensitiveComparer())

    Dim output As New System.Text.StringBuilder
    For Each fruit As String In query
        output.AppendLine(fruit)
    Next

    ' Display the results.
    MsgBox(output.ToString())
End Sub

' This code produces the following output:

' apPLe
' apple
' APple
' apPLE
' orange
' ORANGE
' baNanA
' BAnana

注解

此方法至少有一个类型参数,其类型 Expression<TDelegate> 参数为类型之 Func<T,TResult> 一。 For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

该方法ThenBy<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>)生成一个表示调用ThenBy<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>)本身为构造泛型方法的一个MethodCallExpression方法。 然后,MethodCallExpressionCreateQuery<TElement>(Expression)它将传递给由参数属性source表示Provider的方法IQueryProvider。 调用 CreateQuery<TElement>(Expression) 的结果将强制转换为类型 IOrderedQueryable<T> 并返回。

执行表示调用 ThenBy<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) 的表达式树导致的查询行为取决于参数类型的 source 实现。 预期行为是,它根据调用每个元素source获取keySelector的键执行降序的元素的source辅助排序。 保留以前建立的所有排序顺序。 该 comparer 参数用于比较键值。

适用于