本文整理匯總了C#中System.Linq.Queryable.DefaultIfEmpty方法的典型用法代碼示例。如果您正苦於以下問題：C# Queryable.DefaultIfEmpty方法的具體用法？C# Queryable.DefaultIfEmpty怎麽用？C# Queryable.DefaultIfEmpty使用的例子？那麽, 這裏精選的方法代碼示例或許可以為您提供幫助。
在下文中一共展示了Queryable.DefaultIfEmpty方法的2個代碼示例，這些例子默認根據受歡迎程度排序。您可以為喜歡或者感覺有用的代碼點讚，您的評價將有助於係統推薦出更棒的C#代碼示例。
示例1: DefaultIfEmptyEx1
class Pet
{
public string Name { get; set; }
public int Age { get; set; }
}
public static void DefaultIfEmptyEx1()
{
// Create a list of Pet objects.
List<Pet> pets =
new List<Pet>{ new Pet { Name="Barley", Age=8 },
new Pet { Name="Boots", Age=4 },
new Pet { Name="Whiskers", Age=1 } };
// Call DefaultIfEmtpy() on the collection that Select()
// returns, so that if the initial list is empty, there
// will always be at least one item in the returned array.
string[] names =
pets.AsQueryable()
.Select(pet => pet.Name)
.DefaultIfEmpty()
.ToArray();
string first = names[0];
Console.WriteLine(first);
}輸出：
Barley
示例2: catch
// Create a list of Pet objects.
List<Pet> pets =
new List<Pet>{ new Pet { Name="Barley", Age=8 },
new Pet { Name="Boots", Age=4 },
new Pet { Name="Whiskers", Age=1 } };
// This query selects only those pets that are 10 or older.
// In case there are no pets that meet that criteria, call
// DefaultIfEmpty(). This code passes an (optional) default
// value to DefaultIfEmpty().
string[] oldPets =
pets.AsQueryable()
.Where(pet => pet.Age >= 10)
.Select(pet => pet.Name)
.DefaultIfEmpty("[EMPTY]")
.ToArray();
Console.WriteLine("First query: " + oldPets[0]);
// This query selects only those pets that are 10 or older.
// This code does not call DefaultIfEmpty().
string[] oldPets2 =
pets.AsQueryable()
.Where(pet => pet.Age >= 10)
.Select(pet => pet.Name)
.ToArray();
// There may be no elements in the array, so directly
// accessing element 0 may throw an exception.
try
{
Console.WriteLine("Second query: " + oldPets2[0]);
}
catch (Exception e)
{
Console.WriteLine("Second query: An exception was thrown: " + e.Message);
}輸出：
First query: [EMPTY]
Second query: An exception was thrown: Index was outside the bounds of the array.