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HOW TO：執行物件的延遲初始化

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System.Lazy<T> 類別使得將物件延遲初始化和延遲執行個體化的工作變得簡單。 藉由將物件延遲初始化，您不必再事先建立可能永遠都用不到的物件，而且可以將物件延到初次存取該物件時再初始化。 如需詳細資訊，請參閱延遲初始設定。

範例

下列範例示範如何使用 Lazy<T> 來初始化一個值。 假設依據將 someCondition 變數設為 true 或 false 的其他某個程式碼而定，可能不需要延遲變數。

    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);
  }, LazyExecutionMode.EnsureSingleThreadSafeExecution);

  // 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");
      }
}

下列範例示範如何使用 System.Threading.ThreadLocal<T> 類別，初始化只有目前執行緒上的目前物件執行個體可見的型別。

    '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

//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];

請參閱

參考

System.Threading.LazyInitializer

概念

延遲初始設定