MessageQueue.Peek 方法

public:
 System::Messaging::Message ^ Peek();

public System.Messaging.Message Peek();

member this.Peek : unit -> System.Messaging.Message

Public Function Peek () As Message

傳回

the Message that 代表隊列中的第一個訊息。

例外狀況

範例

以下範例在隊列上使用該 Peek 方法。

在第一個例子中，應用程式會等待佇列中有訊息可用。 請注意，第一個範例並未存取抵達的訊息;它只是暫停處理，直到訊息抵達。 如果訊息已經存在於佇列中，該訊息會立即返回。

在第二個例子中，包含應用程式定義 Order 類別的訊息會被送入佇列，然後從佇列中偷看。

#using <system.dll>
#using <system.messaging.dll>

using namespace System;
using namespace System::Messaging;

// This class represents an object the following example 
// sends to a queue and receives from a queue.
ref class Order
{
public:
   int orderId;
   DateTime orderTime;
};


/// <summary>
/// Provides a container class for the example.
/// </summary>
ref class MyNewQueue
{
public:

   //*************************************************
   // Posts a notification when a message arrives in 
   // the queue S"monitoredQueue". Does not retrieve any 
   // message information when peeking the message.
   //*************************************************
   void NotifyArrived()
   {
      // Connect to a queue.
      MessageQueue^ myQueue = gcnew MessageQueue( ".\\monitoredQueue" );

      // Specify to retrieve no message information.
      myQueue->MessageReadPropertyFilter->ClearAll();

      // Wait for a message to arrive. 
      Message^ emptyMessage = myQueue->Peek();

      // Post a notification when a message arrives.
      Console::WriteLine( "A message has arrived in the queue." );
      return;
   }


   //*************************************************
   // Sends an Order to a queue.
   //*************************************************
   void SendMessage()
   {
      // Create a new order and set values.
      Order^ sentOrder = gcnew Order;
      sentOrder->orderId = 3;
      sentOrder->orderTime = DateTime::Now;

      // Connect to a queue on the local computer.
      MessageQueue^ myQueue = gcnew MessageQueue( ".\\myQueue" );

      // Send the Order to the queue.
      myQueue->Send( sentOrder );
      return;
   }

   //*************************************************
   // Peeks a message containing an Order.
   //*************************************************
   void PeekFirstMessage()
   {
      // Connect to a queue.
      MessageQueue^ myQueue = gcnew MessageQueue( ".\\myQueue" );

      // Set the formatter to indicate the body contains an Order.
      array<Type^>^p = gcnew array<Type^>(1);
      p[ 0 ] = Order::typeid;
      myQueue->Formatter = gcnew XmlMessageFormatter( p );
      try
      {
         // Peek and format the message. 
         Message^ myMessage = myQueue->Peek();
         Order^ myOrder = static_cast<Order^>(myMessage->Body);

         // Display message information.
         Console::WriteLine( "Order ID: {0}", myOrder->orderId );
         Console::WriteLine( "Sent: {0}", myOrder->orderTime );
      }
      catch ( MessageQueueException^ ) 
      {
         // Handle Message Queuing exceptions.
      }
      // Handle invalid serialization format.
      catch ( InvalidOperationException^ e ) 
      {
         Console::WriteLine( e->Message );
      }

      // Catch other exceptions as necessary.
      return;
   }
};

//*************************************************
// Provides an entry point into the application.
//         
// This example posts a notification that a message
// has arrived in a queue. It sends a message 
// containing an other to a separate queue, and then
// peeks the first message in the queue.
//*************************************************
int main()
{
   // Create a new instance of the class.
   MyNewQueue^ myNewQueue = gcnew MyNewQueue;

   // Wait for a message to arrive in the queue.
   myNewQueue->NotifyArrived();

   // Send a message to a queue.
   myNewQueue->SendMessage();

   // Peek the first message in the queue.
   myNewQueue->PeekFirstMessage();
   return 0;
}

using System;
using System.Messaging;

namespace MyProject
{

    // This class represents an object the following example
    // sends to a queue and receives from a queue.
    public class Order
    {
        public int orderId;
        public DateTime orderTime;
    };	

    /// <summary>
    /// Provides a container class for the example.
    /// </summary>
    public class MyNewQueue
    {

        //**************************************************
        // Provides an entry point into the application.
        //		
        // This example posts a notification that a message
        // has arrived in a queue. It sends a message
        // containing an other to a separate queue, and then
        // peeks the first message in the queue.
        //**************************************************

        public static void Main()
        {
            // Create a new instance of the class.
            MyNewQueue myNewQueue = new MyNewQueue();

            // Wait for a message to arrive in the queue.
            myNewQueue.NotifyArrived();

            // Send a message to a queue.
            myNewQueue.SendMessage();	

            // Peek the first message in the queue.
            myNewQueue.PeekFirstMessage();
                        
            return;
        }

        //**************************************************
        // Posts a notification when a message arrives in
        // the queue "monitoredQueue". Does not retrieve any
        // message information when peeking the message.
        //**************************************************
        
        public void NotifyArrived()
        {

            // Connect to a queue.
            MessageQueue myQueue = new
                MessageQueue(".\\monitoredQueue");
    
            // Specify to retrieve no message information.
            myQueue.MessageReadPropertyFilter.ClearAll();

            // Wait for a message to arrive.
            Message emptyMessage = myQueue.Peek();

            // Post a notification when a message arrives.
            Console.WriteLine("A message has arrived in the queue.");

            return;
        }

        //**************************************************
        // Sends an Order to a queue.
        //**************************************************
        
        public void SendMessage()
        {
            
            // Create a new order and set values.
            Order sentOrder = new Order();
            sentOrder.orderId = 3;
            sentOrder.orderTime = DateTime.Now;

            // Connect to a queue on the local computer.
            MessageQueue myQueue = new MessageQueue(".\\myQueue");

            // Send the Order to the queue.
            myQueue.Send(sentOrder);

            return;
        }

        //**************************************************
        // Peeks a message containing an Order.
        //**************************************************
        
        public void PeekFirstMessage()
        {
            // Connect to a queue.
            MessageQueue myQueue = new MessageQueue(".\\myQueue");
    
            // Set the formatter to indicate the body contains an Order.
            myQueue.Formatter = new XmlMessageFormatter(new Type[]
                {typeof(MyProject.Order)});
            
            try
            {
                // Peek and format the message.
                Message myMessage =	myQueue.Peek();
                Order myOrder = (Order)myMessage.Body;

                // Display message information.
                Console.WriteLine("Order ID: " +
                    myOrder.orderId.ToString());
                Console.WriteLine("Sent: " +
                    myOrder.orderTime.ToString());
            }
            
            catch (MessageQueueException)
            {
                // Handle Message Queuing exceptions.
            }

            // Handle invalid serialization format.
            catch (InvalidOperationException e)
            {
                Console.WriteLine(e.Message);
            }
            
            // Catch other exceptions as necessary.

            return;
        }
    }
}

Imports System.Messaging



    ' This class represents an object the following example 
    ' sends to a queue and peeks from a queue.
    Public Class Order
        Public orderId As Integer
        Public orderTime As DateTime
    End Class


   
    Public Class MyNewQueue


        
        ' Provides an entry point into the application.
        '		 
        ' This example posts a notification that a message
        ' has arrived in a queue. It sends a message 
        ' containing an other to a separate queue, and then
        ' peeks the first message in the queue.
        

        Public Shared Sub Main()

            ' Create a new instance of the class.
            Dim myNewQueue As New MyNewQueue()

            ' Wait for a message to arrive in the queue.
            myNewQueue.NotifyArrived()

            ' Send a message to a queue.
            myNewQueue.SendMessage()

            ' Peek the first message in the queue.
            myNewQueue.PeekFirstMessage()

            Return

        End Sub


        
        ' Posts a notification when a message arrives in 
        ' the queue "monitoredQueue". Does not retrieve any 
        ' message information when peeking the message.
        
        Public Sub NotifyArrived()

            ' Connect to a queue.
            Dim myQueue As New MessageQueue(".\monitoredQueue")

            ' Specify to retrieve no message information.
            myQueue.MessageReadPropertyFilter.ClearAll()

            ' Wait for a message to arrive. 
            Dim emptyMessage As Message = myQueue.Peek()

            ' Post a notification when a message arrives.
            Console.WriteLine("A message has arrived in the queue.")

            Return

        End Sub


        
        ' Sends an Order to a queue.
        

        Public Sub SendMessage()

            ' Create a new order and set values.
            Dim sentOrder As New Order()
            sentOrder.orderId = 3
            sentOrder.orderTime = DateTime.Now

            ' Connect to a queue on the local computer.
            Dim myQueue As New MessageQueue(".\myQueue")

            ' Send the Order to the queue.
            myQueue.Send(sentOrder)

            Return

        End Sub


        
        ' Peeks a message containing an Order.
        

        Public Sub PeekFirstMessage()

            ' Connect to a queue.
            Dim myQueue As New MessageQueue(".\myQueue")

            ' Set the formatter to indicate body contains an Order.
            myQueue.Formatter = New XmlMessageFormatter(New Type() _
                {GetType(Order)})

            Try

                ' Peek and format the message. 
                Dim myMessage As Message = myQueue.Peek()
                Dim myOrder As Order = CType(myMessage.Body, Order)

                ' Display message information.
                Console.WriteLine(("Order ID: " + _
                    myOrder.orderId.ToString()))
                Console.WriteLine(("Sent: " + _
                    myOrder.orderTime.ToString()))

            Catch m as MessageQueueException
                ' Handle Message Queuing exceptions.


            Catch e As InvalidOperationException
                ' Handle invalid serialization format.
                Console.WriteLine(e.Message)

                ' Catch other exceptions as necessary.

            End Try

            Return

        End Sub

End Class

備註

利用此超載來窺探佇列，或等待佇列中出現訊息。

該 Peek 方法會讀取，但不會移除佇列中的第一個訊息。 因此，除非有更高優先權的訊息抵達佇列，否則會反覆呼叫以回 Peek 傳相同的訊息。 而此 Receive 方法則同時讀取並移除第一則訊息。 重複呼叫 Receive，因此會返回不同的訊息。

訊息排隊會依優先順序和抵達時間排序排隊中的訊息。 只有當新訊息優先權較高時，才會將其置於舊訊息之前。

當目前執行緒在等待訊息到達隊列時被封鎖，才會使用 Peek 。 由於此超載未指定逾時，應用程式可能會無限期等待。 如果你需要申請流程繼續而不等，請使用非同步 BeginPeek 方法。 或者，你也可以利用指定逾時的超載來指定訊息到達佇列的逾時 Peek 。

下表顯示此方法是否可在多種工作群組模式中使用。

另請參閱

• Receive()
• BeginPeek()

public:
 System::Messaging::Message ^ Peek(TimeSpan timeout);

public System.Messaging.Message Peek(TimeSpan timeout);

member this.Peek : TimeSpan -> System.Messaging.Message

Public Function Peek (timeout As TimeSpan) As Message

參數

傳回

the Message that 代表隊列中的第一個訊息。

例外狀況

範例

以下程式碼範例使用 Peek 逾時為零的方法來檢查佇列是否為空。

#using <system.dll>
#using <system.messaging.dll>

using namespace System;
using namespace System::Messaging;
ref class MyNewQueue
{
public:

   //*************************************************
   // Determines whether a queue is empty. The Peek()
   // method throws an exception if there is no message
   // in the queue. This method handles that exception 
   // by returning true to the calling method.
   //*************************************************
   bool IsQueueEmpty()
   {
      bool isQueueEmpty = false;
      
      // Connect to a queue.
      MessageQueue^ myQueue = gcnew MessageQueue( ".\\myQueue" );
      try
      {
         
         // Set Peek to return immediately.
         myQueue->Peek( TimeSpan(0) );
         
         // If an IOTime->Item[Out] was* not thrown, there is a message 
         // in the queue.
         isQueueEmpty = false;
      }
      catch ( MessageQueueException^ e ) 
      {
         if ( e->MessageQueueErrorCode == MessageQueueErrorCode::IOTimeout )
         {
            
            // No message was in the queue.
            isQueueEmpty = true;
         }

         
         // Handle other sources of MessageQueueException.
      }

      
      // Handle other exceptions as necessary.
      // Return true if there are no messages in the queue.
      return isQueueEmpty;
   }

};


//*************************************************
// Provides an entry point into the application.
//         
// This example determines whether a queue is empty.
//*************************************************
int main()
{
   
   // Create a new instance of the class.
   MyNewQueue^ myNewQueue = gcnew MyNewQueue;
   
   // Determine whether a queue is empty.
   bool isQueueEmpty = myNewQueue->IsQueueEmpty();
   return 0;
}

using System;
using System.Messaging;

namespace MyProject
{
    /// <summary>
    /// Provides a container class for the example.
    /// </summary>
    public class MyNewQueue
    {

        //**************************************************
        // Provides an entry point into the application.
        //		
        // This example determines whether a queue is empty.
        //**************************************************

        public static void Main()
        {
            // Create a new instance of the class.
            MyNewQueue myNewQueue = new MyNewQueue();

            // Determine whether a queue is empty.
            bool isQueueEmpty = myNewQueue.IsQueueEmpty();
                        
            return;
        }

        //**************************************************
        // Determines whether a queue is empty. The Peek()
        // method throws an exception if there is no message
        // in the queue. This method handles that exception
        // by returning true to the calling method.
        //**************************************************
        
        public bool IsQueueEmpty()
        {
            bool isQueueEmpty = false;

            // Connect to a queue.
            MessageQueue myQueue = new MessageQueue(".\\myQueue");

            try
            {
                // Set Peek to return immediately.
                myQueue.Peek(new TimeSpan(0));

                // If an IOTimeout was not thrown, there is a message
                // in the queue.
                isQueueEmpty = false;
            }

            catch(MessageQueueException e)
            {
                if (e.MessageQueueErrorCode ==
                    MessageQueueErrorCode.IOTimeout)
                {
                    // No message was in the queue.
                    isQueueEmpty = true;
                }

                // Handle other sources of MessageQueueException.
            }

            // Handle other exceptions as necessary.

            // Return true if there are no messages in the queue.
            return isQueueEmpty;
        }
    }
}

Imports System.Messaging



   
    Public Class MyNewQueue


        '
        ' Provides an entry point into the application.
        '		 
        ' This example determines whether a queue is empty.
        '

        Public Shared Sub Main()

            ' Create a new instance of the class.
            Dim myNewQueue As New MyNewQueue()

            ' Determine whether a queue is empty.
            Dim IsQueueEmpty As Boolean = myNewQueue.IsQueueEmpty()
        if IsQueueEMpty=True Then Console.WriteLine("Empty")
            

            Return

        End Sub


        '
        ' Determines whether a queue is empty. The Peek()
        ' method throws an exception if there is no message
        ' in the queue. This method handles that exception 
        ' by returning true to the calling method.
        '

        Public Function IsQueueEmpty() As Boolean

            'Dim QueueEmpty As Boolean = False

            ' Connect to a queue.
            Dim myQueue As New MessageQueue(".\myQueue")

            Try

                ' Set Peek to return immediately.
                myQueue.Peek(New TimeSpan(0))

                ' If an IOTimeout was not thrown, there is a message 
                ' in the queue.
                'queueEmpty = False

            Catch e As MessageQueueException

                If e.MessageQueueErrorCode = _
                    MessageQueueErrorCode.IOTimeout Then

                    ' No message was in the queue.
                    IsQueueEmpty = True

                End If

                ' Handle other sources of MessageQueueException as necessary.

                ' Handle other exceptions as necessary.

            End Try

            ' Return true if there are no messages in the queue.
            'Return queueEmpty
        IsQueueEmpty = False

        End Function 'IsQueueEmpty 

End Class

備註

利用此超載方式窺探佇列，或等待指定時間直到隊列中出現訊息。 如果佇列中已有訊息，該方法會立即回傳。

該 Peek 方法會讀取，但不會移除佇列中的第一個訊息。 因此，除非有更高優先權的訊息抵達佇列，否則會反覆呼叫以回 Peek 傳相同的訊息。 而此 Receive 方法則同時讀取並移除第一則訊息。 重複呼叫 Receive，因此會返回不同的訊息。

訊息排隊會依優先順序和抵達時間排序排隊中的訊息。 只有當新訊息優先權較高時，才會將其置於舊訊息之前。

當目前執行緒在等待訊息到達隊列時被封鎖，才會使用 Peek 。 該討論串會在指定時間內被封鎖，若你指定 InfiniteTimeout，則無限期封鎖。 如果你需要申請流程繼續而不等，請使用非同步 BeginPeek 方法。

下表顯示此方法是否可在多種工作群組模式中使用。

另請參閱

• InfiniteTimeout
• Receive()
• BeginPeek()

public:
 System::Messaging::Message ^ Peek(TimeSpan timeout, System::Messaging::Cursor ^ cursor, System::Messaging::PeekAction action);

public System.Messaging.Message Peek(TimeSpan timeout, System.Messaging.Cursor cursor, System.Messaging.PeekAction action);

member this.Peek : TimeSpan * System.Messaging.Cursor * System.Messaging.PeekAction -> System.Messaging.Message

Public Function Peek (timeout As TimeSpan, cursor As Cursor, action As PeekAction) As Message

參數

傳回

Message代表佇列中的訊息。

例外狀況

備註

利用此超載方式窺探佇列，或等待指定時間直到隊列中出現訊息。 如果佇列中已有訊息，該方法會立即回傳。

該 Peek 方法會讀取但不會移除佇列中的訊息。 而此 Receive 方法則同時讀取並移除佇列中的訊息。

當目前執行緒在等待訊息到達隊列時被封鎖，才會使用 Peek 。 該執行緒會在指定時間內被封鎖，或如果你指定 InfiniteTimeout為 則無限期封鎖。 如果你需要申請流程繼續而不等，請使用非同步 BeginPeek 方法。

下表顯示此方法是否可在多種工作群組模式中使用。

另請參閱

• Cursor
• PeekAction
• InfiniteTimeout
• Receive()
• BeginPeek()