AppContext.TryGetSwitch(String, Boolean) 方法

public:
 static bool TryGetSwitch(System::String ^ switchName, [Runtime::InteropServices::Out] bool % isEnabled);

public static bool TryGetSwitch(string switchName, out bool isEnabled);

static member TryGetSwitch : string * bool -> bool

Public Shared Function TryGetSwitch (switchName As String, ByRef isEnabled As Boolean) As Boolean

參數

傳回

true 若 switchName 被設定 isEnabled 且參數包含交換器值;否則， false。

例外狀況

範例

以下範例判斷函式庫使用者是否設定了一個名為 Switch.AmazingLib.ThrowOnException的交換器。

public class AmazingLib
{
   private bool shouldThrow;

   public void PerformAnOperation()
   {
      if (!AppContext.TryGetSwitch("Switch.AmazingLib.ThrowOnException", out shouldThrow)) {
         // This is the case where the switch value was not set by the application.
         // The library can choose to get the value of shouldThrow by other means.
         // If no overrides or default values are specified, the value should be 'false'.
         // A false value implies the latest behavior.
      }

      // The library can use the value of shouldThrow to throw exceptions or not.
      if (shouldThrow) {
         // old code
      }
      else {
          // new code
      }
   }
}

module AmazingLib =
    let performAnOperation () =
        match AppContext.TryGetSwitch "Switch.AmazingLib.ThrowOnException" with
        | false, _ ->
            // This is the case where the switch value was not set by the application.
            // The library can choose to get the value of shouldThrow by other means.
            // If no overrides or default values are specified, the value should be 'false'.
            // A false value implies the latest behavior.
            ()
        | true, shouldThrow ->
            // The library can use the value of shouldThrow to throw exceptions or not.
            if shouldThrow then
                // old code
                ()
            else
                // new code
                ()

Public Class AmazingLib

   Private shouldThrow As Boolean

   Public Sub PerformAnOperation()
      If Not AppContext.TryGetSwitch("Switch.AmazingLib.ThrowOnException", shouldThrow) Then 
         ' This is the case where the switch value was not set by the application. 
         ' The library can choose to get the value of shouldThrow by other means. 
         ' If no overrides or default values are specified, the value should be 'false'. 
         ' A false value implies the latest behavior.
      End If

      ' The library can use the value of shouldThrow to throw exceptions or not.
      If shouldThrow Then
         ' old code
      Else 
          ' new code
      End If
   End Sub
End Class

備註

AppContext 類別可讓程式庫開發者為其使用者提供統一的退出機制。 它會建立元件之間的鬆散結合合約，以傳達退出要求。 當對現有功能進行變更時，這項功能通常很重要。 相反地，對於新功能來說，已經有隱含的默認同意。

通用語言執行時會自動讀取登錄檔和應用程式的設定檔，來填入分配給實 AppContext 例的交換器。 這些交換器的值可以被覆蓋，並新增交換器，方法是呼叫該 SetSwitch 方法。

函式庫呼叫該 TryGetSwitch 方法以檢查其使用者是否宣告了交換器的值，然後對此適當行動。 預設情況下，如果交換器未定義，新功能會被啟用。 若交換器定義且其值為 false，則新功能也會被啟用。 若其值為 true，則啟用舊有行為。

另請參閱

• SetSwitch(String, Boolean)