作法：執行物件的延遲初始設定
System.Lazy<T> 類別可簡化執行物件延遲初始化和具現化的工作。 以延遲方式初始化物件時，您可以避免必須在永不需要這些物件時完全建立它們，也可以延後其初始化作業，直到第一次存取這些物件為止。 如需詳細資訊，請參閱延遲初始化。
範例 1
下列範例示範如何使用 Lazy<T> 來初始化值。 假設可能不需要延遲變數，這取決於某個將 someCondition 變數設定為 true 或 false 的其他程式碼。
Dim someCondition As Boolean = False
Sub Main()
'Initializing a value with a big computation, computed in parallel
Dim _data As Lazy(Of Integer) = New Lazy(Of Integer)(Function()
Dim result =
ParallelEnumerable.Range(0, 1000).
Aggregate(Function(x, y)
Return x + y
End Function)
Return result
End Function)
' do work that may or may not set someCondition to True
' ...
' Initialize the data only if needed
If someCondition = True Then
If (_data.Value > 100) Then
Console.WriteLine("Good data")
End If
End If
End Sub
static bool someCondition = false;
//Initializing a value with a big computation, computed in parallel
Lazy<int> _data = new Lazy<int>(delegate
{
return ParallelEnumerable.Range(0, 1000).
Select(i => Compute(i)).Aggregate((x,y) => x + y);
}, LazyThreadSafetyMode.ExecutionAndPublication);
// Do some work that may or may not set someCondition to true.
// ...
// Initialize the data only if necessary
if (someCondition)
{
if (_data.Value > 100)
{
Console.WriteLine("Good data");
}
}
範例 2
下列範例示範如何使用 System.Threading.ThreadLocal<T> 類別來初始化類型，只有在目前執行緒上的目前物件執行個體中才能看見該類型。
//Initializing a value per thread, per instance
ThreadLocal<int[][]> _scratchArrays =
new ThreadLocal<int[][]>(InitializeArrays);
// . . .
static int[][] InitializeArrays () {return new int[][]}
// . . .
// use the thread-local data
int i = 8;
int [] tempArr = _scratchArrays.Value[i];
'Initializing a value per thread, per instance
Dim _scratchArrays =
New ThreadLocal(Of Integer()())(Function() InitializeArrays())
' use the thread-local data
Dim tempArr As Integer() = _scratchArrays.Value(i)
' ...
End Sub
Function InitializeArrays() As Integer()()
Dim result(10)() As Integer
' Initialize the arrays on the current thread.
' ...
Return result
End Function
