Queryable.TakeWhile 方法

定義

只要指定的條件為 true,就會傳回序列中的項目,然後略過其餘項目。Returns elements from a sequence as long as a specified condition is true, and then skips the remaining elements.

多載

TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)

只要指定的條件為 true,就會傳回序列中的項目。Returns elements from a sequence as long as a specified condition is true.

TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>)

只要指定的條件為 true,就會傳回序列中的項目。Returns elements from a sequence as long as a specified condition is true. 項目的索引是用於述詞功能的邏輯中。The element's index is used in the logic of the predicate function.

TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)

只要指定的條件為 true,就會傳回序列中的項目。Returns elements from a sequence as long as a specified condition is true.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IQueryable<TSource> ^ TakeWhile(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, bool> ^> ^ predicate);
public static System.Linq.IQueryable<TSource> TakeWhile<TSource> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,bool>> predicate);
static member TakeWhile : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, bool>> -> System.Linq.IQueryable<'Source>
<Extension()>
Public Function TakeWhile(Of TSource) (source As IQueryable(Of TSource), predicate As Expression(Of Func(Of TSource, Boolean))) As IQueryable(Of TSource)

類型參數

TSource

source 項目的類型。The type of the elements of source.

參數

source
IQueryable<TSource>

傳回項目的序列。The sequence to return elements from.

predicate
Expression<Func<TSource,Boolean>>

用來測試每個項目是否符合條件的函式。A function to test each element for a condition.

傳回

IQueryable<TSource>

IQueryable<T>,其中包含輸入序列中的項目,而這些項目出現在已無法通過 predicate 所指定之測試的項目前面。An IQueryable<T> that contains elements from the input sequence occurring before the element at which the test specified by predicate no longer passes.

例外狀況

sourcepredicatenullsource or predicate is null.

範例

下列程式碼範例將示範如何使用 TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) ,只要條件為 true,就會從序列的開頭傳回元素。The following code example demonstrates how to use TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) to return elements from the start of a sequence as long as a condition is true.

string[] fruits = { "apple", "banana", "mango", "orange",
                      "passionfruit", "grape" };

// Take strings from the array until a string
// that is equal to "orange" is found.
IEnumerable<string> query =
    fruits.AsQueryable()
    .TakeWhile(fruit => String.Compare("orange", fruit, true) != 0);

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

/*
    This code produces the following output:

    apple
    banana
    mango
*/
Dim fruits() As String = {"apple", "banana", "mango", "orange", _
                      "passionfruit", "grape"}

' Take strings from the array until a string
' that is equal to "orange" is found.
Dim query = fruits.AsQueryable() _
    .TakeWhile(Function(fruit) String.Compare("orange", fruit, True) <> 0)

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

' Display the output.
MsgBox(output.ToString())

'This code produces the following output:

'apple
'banana
'mango

備註

這個方法至少有一個類型的參數 Expression<TDelegate> ,其型別引數是其中一種 Func<T,TResult> 類型。This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. 針對這些參數,您可以傳入 lambda 運算式,並將其編譯為 Expression<TDelegate>For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)方法 MethodCallExpression 會產生,代表呼叫 TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 本身做為已建立的泛型方法。The TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) method generates a MethodCallExpression that represents calling TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) itself as a constructed generic method. 然後,它會將傳遞 MethodCallExpression 給以 CreateQuery(Expression) 參數的屬性所表示的方法 IQueryProvider Provider sourceIt then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

執行表示呼叫的運算式樹狀架構所產生的查詢行為, TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 取決於參數類型的實作為 sourceThe query behavior that occurs as a result of executing an expression tree that represents calling TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) depends on the implementation of the type of the source parameter. 預期的行為是它會套用 predicate 至中的每個專案,直到找到傳回的專案 source 為止 predicate falseThe expected behavior is that it applies predicate to each element in source until it finds an element for which predicate returns false. 它會傳回所有元素直到該點為止。It returns all the elements up until that point.

適用於

TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>)

只要指定的條件為 true,就會傳回序列中的項目。Returns elements from a sequence as long as a specified condition is true. 項目的索引是用於述詞功能的邏輯中。The element's index is used in the logic of the predicate function.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IQueryable<TSource> ^ TakeWhile(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, int, bool> ^> ^ predicate);
public static System.Linq.IQueryable<TSource> TakeWhile<TSource> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,int,bool>> predicate);
static member TakeWhile : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, int, bool>> -> System.Linq.IQueryable<'Source>
<Extension()>
Public Function TakeWhile(Of TSource) (source As IQueryable(Of TSource), predicate As Expression(Of Func(Of TSource, Integer, Boolean))) As IQueryable(Of TSource)

類型參數

TSource

source 項目的類型。The type of the elements of source.

參數

source
IQueryable<TSource>

傳回項目的序列。The sequence to return elements from.

predicate
Expression<Func<TSource,Int32,Boolean>>

用來測試各項目是否符合條件的函式;此函式的第二個參數代表來源序列中項目的索引。A function to test each element for a condition; the second parameter of the function represents the index of the element in the source sequence.

傳回

IQueryable<TSource>

IQueryable<T>,其中包含輸入序列中的項目,而這些項目出現在已無法通過 predicate 所指定之測試的項目前面。An IQueryable<T> that contains elements from the input sequence occurring before the element at which the test specified by predicate no longer passes.

例外狀況

sourcepredicatenullsource or predicate is null.

範例

下列程式碼範例將示範如何使用 TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) 來從序列的開頭傳回專案,只要使用專案索引的條件為 true 即可。The following code example demonstrates how to use TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) to return elements from the start of a sequence as long as a condition that uses the index of the element is true.

string[] fruits = { "apple", "passionfruit", "banana", "mango",
                      "orange", "blueberry", "grape", "strawberry" };

// Take strings from the array until a string whose length
// is less than its index in the array is found.
IEnumerable<string> query =
    fruits.AsQueryable()
    .TakeWhile((fruit, index) => fruit.Length >= index);

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

/*
    This code produces the following output:

    apple
    passionfruit
    banana
    mango
    orange
    blueberry
*/
Dim fruits() As String = _
    {"apple", "passionfruit", "banana", "mango", _
     "orange", "blueberry", "grape", "strawberry"}

' Take strings from the array until a string whose length
' is less than its index in the array is found.
Dim query = fruits.AsQueryable() _
    .TakeWhile(Function(fruit, index) fruit.Length >= index)

' Display the results.
Dim output As New System.Text.StringBuilder
For Each fruit As String In query
    output.AppendLine(fruit)
Next
MsgBox(output.ToString())

' This code produces the following output:

' apple
' passionfruit
' banana
' mango
' orange
' blueberry

備註

這個方法至少有一個類型的參數 Expression<TDelegate> ,其型別引數是其中一種 Func<T,TResult> 類型。This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. 針對這些參數,您可以傳入 lambda 運算式,並將其編譯為 Expression<TDelegate>For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>)方法 MethodCallExpression 會產生,代表呼叫 TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) 本身做為已建立的泛型方法。The TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) method generates a MethodCallExpression that represents calling TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) itself as a constructed generic method. 然後,它會將傳遞 MethodCallExpression 給以 CreateQuery(Expression) 參數的屬性所表示的方法 IQueryProvider Provider sourceIt then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

執行表示呼叫的運算式樹狀架構所產生的查詢行為, TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) 取決於參數類型的實作為 sourceThe query behavior that occurs as a result of executing an expression tree that represents calling TakeWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) depends on the implementation of the type of the source parameter. 預期的行為是它會套用 predicate 至中的每個專案,直到找到傳回的專案 source 為止 predicate falseThe expected behavior is that it applies predicate to each element in source until it finds an element for which predicate returns false. 它會傳回所有元素直到該點為止。It returns all the elements up until that point. 每個來源元素的索引都會作為的第二個引數提供 predicateThe index of each source element is provided as the second argument to predicate.

適用於