NullReferenceException NullReferenceException NullReferenceException NullReferenceException Class

Definición

public ref class NullReferenceException : SystemException

[System.Runtime.InteropServices.ComVisible(true)]
[System.Serializable]
public class NullReferenceException : SystemException

type NullReferenceException = class
    inherit SystemException

Public Class NullReferenceException
Inherits SystemException

Herencia

ObjectObjectObjectObject

ExceptionExceptionExceptionException

SystemExceptionSystemExceptionSystemExceptionSystemException

NullReferenceExceptionNullReferenceExceptionNullReferenceExceptionNullReferenceException

Atributos

ComVisibleAttribute SerializableAttribute

Comentarios

Un NullReferenceException excepción se produce cuando se intenta tener acceso a un miembro en un tipo cuyo valor es null.A NullReferenceException exception is thrown when you try to access a member on a type whose value is null. Un NullReferenceException excepción normalmente refleja el error de desarrollador y se produce en los escenarios siguientes:A NullReferenceException exception typically reflects developer error and is thrown in the following scenarios:

• Ha olvidado crear instancias de un tipo de referencia.You've forgotten to instantiate a reference type. En el ejemplo siguiente, names se declara pero nunca se crea:In the following example, names is declared but never instantiated:

  using System;
  using System.Collections.Generic;
  
  public class Example
  {
     public static void Main(string[] args)
     {
        int value = Int32.Parse(args[0]);
        List<String> names;
        if (value > 0)
           names = new List<String>();
        
        names.Add("Major Major Major");       
     }
  }
  // Compilation displays a warning like the following:
  //    Example1.cs(10) : warning BC42104: Variable //names// is used before it 
  //    has been assigned a value. A null reference exception could result 
  //    at runtime.
  //    
  //          names.Add("Major Major Major")
  //          ~~~~~
  // The example displays output like the following output:
  //    Unhandled Exception: System.NullReferenceException: Object reference 
  //    not set to an instance of an object.
  //       at Example.Main()
  

  Imports System.Collections.Generic
  
  Module Example
     Public Sub Main()
        Dim names As List(Of String)
        names.Add("Major Major Major")       
     End Sub
  End Module
  ' Compilation displays a warning like the following:
  '    Example1.vb(10) : warning BC42104: Variable 'names' is used before it 
  '    has been assigned a value. A null reference exception could result 
  '    at runtime.
  '    
  '          names.Add("Major Major Major")
  '          ~~~~~
  ' The example displays output like the following output:
  '    Unhandled Exception: System.NullReferenceException: Object reference 
  '    not set to an instance of an object.
  '       at Example.Main()
  

  Algunos compiladores emiten una advertencia cuando compila este código.Some compilers issue a warning when they compile this code. Otros emiten un error y se produce un error en la compilación.Others issue an error, and the compilation fails. Para solucionar este problema, cree una instancia del objeto para que su valor ya no es null.To address this problem, instantiate the object so that its value is no longer null. El siguiente ejemplo realiza esto llamando al constructor de clase de un tipo.The following example does this by calling a type's class constructor.

  using System;
  using System.Collections.Generic;
  
  public class Example
  {
     public static void Main()
     {
        List<String> names = new List<String>();
        names.Add("Major Major Major");
     }
  }
  

  Imports System.Collections.Generic
  
  Module Example
     Public Sub Main()
        Dim names As New List(Of String)()
        names.Add("Major Major Major")       
     End Sub
  End Module
  

• Ha olvidado a una matriz de dimensión antes de inicializarla.You've forgotten to dimension an array before initializing it. En el ejemplo siguiente, values se declara como una matriz de enteros, pero nunca se especifica el número de elementos que contiene.In the following example, values is declared to be an integer array, but the number of elements that it contains is never specified. El intento de inicializar sus valores, por tanto, se produce un NullReferenceException excepción.The attempt to initialize its values therefore thrown a NullReferenceException exception.

  using System;
  
  public class Example
  {
     public static void Main()
     {
         int[] values = null;
         for (int ctr = 0; ctr <= 9; ctr++)
            values[ctr] = ctr * 2;
            
         foreach (var value in values)
            Console.WriteLine(value);   
     }
  }
  // The example displays the following output:
  //    Unhandled Exception: 
  //       System.NullReferenceException: Object reference not set to an instance of an object.
  //       at Example.Main()
  

  Module Example
     Public Sub Main()
         Dim values() As Integer
         For ctr As Integer = 0 To 9
            values(ctr) = ctr * 2
         Next
            
         For Each value In values
            Console.WriteLine(value)
         Next      
     End Sub
  End Module
  ' The example displays the following output:
  '    Unhandled Exception: 
  '       System.NullReferenceException: Object reference not set to an instance of an object.
  '       at Example.Main()
  

  Puede eliminar la excepción al declarar el número de elementos de la matriz antes de inicializarla, como el siguiente ejemplo.You can eliminate the exception by declaring the number of elements in the array before initializing it, as the following example does.

  using System;
  
  public class Example
  {
     public static void Main()
     {
         int[] values = new int[10];
         for (int ctr = 0; ctr <= 9; ctr++)
            values[ctr] = ctr * 2;
            
         foreach (var value in values)
            Console.WriteLine(value);   
     }
  }
  // The example displays the following output:
  //    0
  //    2
  //    4
  //    6
  //    8
  //    10
  //    12
  //    14
  //    16
  //    18
  

  Module Example
     Public Sub Main()
         Dim values(9) As Integer
         For ctr As Integer = 0 To 9
            values(ctr) = ctr * 2
         Next
            
         For Each value In values
            Console.WriteLine(value)
         Next      
     End Sub
  End Module
  ' The example displays the following output:
  '    0
  '    2
  '    4
  '    6
  '    8
  '    10
  '    12
  '    14
  '    16
  '    18
  

  Para obtener más información sobre cómo declarar e inicializar matrices, vea matrices y matrices.For more information on declaring and initializing arrays, see Arrays and Arrays.

• Obtendrá un null devolver el valor de un método y, a continuación, llamar a un método en el tipo devuelto.You get a null return value from a method, and then call a method on the returned type. A veces esto es el resultado de un error de documentación; se produce un error en la documentación de tener en cuenta que puede devolver una llamada al método null.This sometimes is the result of a documentation error; the documentation fails to note that a method call can return null. En otros casos, el código erróneamente se da por supuesto que el método siempre devolverá una que no sean denull valor.In other cases, your code erroneously assumes that the method will always return a non-null value.

  El código en el ejemplo siguiente se da por supuesto que el Array.Find método siempre devuelve Person cuyo FirstName campo coincide con una cadena de búsqueda.The code in the following example assumes that the Array.Find method always returns Person object whose FirstName field matches a search string. Dado que no hay ninguna coincidencia, el runtime produce una NullReferenceException excepción.Because there is no match, the runtime throws a NullReferenceException exception.

  using System;
  
  public class Example
  {
     public static void Main()
     {
        Person[] persons = Person.AddRange( new String[] { "Abigail", "Abra", 
                                            "Abraham", "Adrian", "Ariella", 
                                            "Arnold", "Aston", "Astor" } );    
        String nameToFind = "Robert";
        Person found = Array.Find(persons, p => p.FirstName == nameToFind);
        Console.WriteLine(found.FirstName);
     }
  }
  
  public class Person
  {
     public static Person[] AddRange(String[] firstNames) 
     {
        Person[] p = new Person[firstNames.Length];
        for (int ctr = 0; ctr < firstNames.Length; ctr++)
           p[ctr] = new Person(firstNames[ctr]);
  
        return p;
     }
     
     public Person(String firstName)
     {
        this.FirstName = firstName;
     } 
     
     public String FirstName;
  }
  // The example displays the following output:
  //       Unhandled Exception: System.NullReferenceException: 
  //       Object reference not set to an instance of an object.
  //          at Example.Main()
  

  Module Example
     Public Sub Main()
        Dim persons() As Person = Person.AddRange( { "Abigail", "Abra",
                                                     "Abraham", "Adrian",
                                                     "Ariella", "Arnold", 
                                                     "Aston", "Astor" } )    
        Dim nameToFind As String = "Robert"
        Dim found As Person = Array.Find(persons, Function(p) p.FirstName = nameToFind)
        Console.WriteLine(found.FirstName)
     End Sub
  End Module
  
  Public Class Person
     Public Shared Function AddRange(firstNames() As String) As Person()
        Dim p(firstNames.Length - 1) As Person
        For ctr As Integer = 0 To firstNames.Length - 1
           p(ctr) = New Person(firstNames(ctr))
        Next   
        Return p
     End Function
     
     Public Sub New(firstName As String)
        Me.FirstName = firstName
     End Sub 
     
     Public FirstName As String
  End Class
  ' The example displays the following output:
  '       Unhandled Exception: System.NullReferenceException: 
  '       Object reference not set to an instance of an object.
  '          at Example.Main()
  

  Para solucionar este problema, pruebe el valor devuelto del método para asegurarse de que no es null antes de llamar a cualquiera de sus miembros, como el siguiente ejemplo.To address this problem, test the method's return value to ensure that it is not null before calling any of its members, as the following example does.

  using System;
  
  public class Example
  {
     public static void Main()
     {
        Person[] persons = Person.AddRange( new String[] { "Abigail", "Abra", 
                                            "Abraham", "Adrian", "Ariella", 
                                            "Arnold", "Aston", "Astor" } );    
        String nameToFind = "Robert";
        Person found = Array.Find(persons, p => p.FirstName == nameToFind);
        if (found != null)
           Console.WriteLine(found.FirstName);
        else
           Console.WriteLine("{0} not found.", nameToFind);   
     }
  }
  
  public class Person
  {
     public static Person[] AddRange(String[] firstNames) 
     {
        Person[] p = new Person[firstNames.Length];
        for (int ctr = 0; ctr < firstNames.Length; ctr++)
           p[ctr] = new Person(firstNames[ctr]);
  
        return p;
     }
     
     public Person(String firstName)
     {
        this.FirstName = firstName;
     } 
     
     public String FirstName;
  }
  // The example displays the following output:
  //        Robert not found
  

  Module Example
     Public Sub Main()
        Dim persons() As Person = Person.AddRange( { "Abigail", "Abra",
                                                     "Abraham", "Adrian",
                                                     "Ariella", "Arnold", 
                                                     "Aston", "Astor" } )    
        Dim nameToFind As String = "Robert"
        Dim found As Person = Array.Find(persons, Function(p) p.FirstName = nameToFind)
        If found IsNot Nothing Then
           Console.WriteLine(found.FirstName)
        Else
           Console.WriteLine("{0} not found.", nameToFind)
        End If   
     End Sub
  End Module
  
  Public Class Person
     Public Shared Function AddRange(firstNames() As String) As Person()
        Dim p(firstNames.Length - 1) As Person
        For ctr As Integer = 0 To firstNames.Length - 1
           p(ctr) = New Person(firstNames(ctr))
        Next   
        Return p
     End Function
     
     Public Sub New(firstName As String)
        Me.FirstName = firstName
     End Sub 
     
     Public FirstName As String
  End Class
  ' The example displays the following output:
  '       Robert not found
  

• Está utilizando una expresión (por ejemplo, va a encadenar una lista de métodos o propiedades juntas) para recuperar un valor y, aunque está comprobando si el valor es null, el tiempo de ejecución todavía inicia un NullReferenceException excepción.You're using an expression (for example, you're chaining a list of methods or properties together) to retrieve a value and, although you're checking whether the value is null, the runtime still throws a NullReferenceException exception. Esto ocurre porque uno de los valores intermedios en la expresión devuelve null.This occurs because one of the intermediate values in the expression returns null. Como resultado, la prueba por null nunca se evalúa.As a result, your test for null is never evaluated.

  En el ejemplo siguiente se define un Pages objeto que almacena en caché información acerca de las páginas web, que se presentan por Page objetos.The following example defines a Pages object that caches information about web pages, which are presented by Page objects. El Example.Main método comprueba si la página web actual tiene un título distinto de null y, si es así, muestra el título.The Example.Main method checks whether the current web page has a non-null title and, if it does, displays the title. A pesar de esta comprobación, sin embargo, el método produce una NullReferenceException excepción.Despite this check, however, the method throws a NullReferenceException exception.

  using System;
  
  public class Example
  {
     public static void Main()
     {
        var pages = new Pages();
        if (! String.IsNullOrEmpty(pages.CurrentPage.Title)) {
           String title = pages.CurrentPage.Title;
           Console.WriteLine("Current title: '{0}'", title);
        }
     }
  }
  
  public class Pages 
  {
     Page[] page = new Page[10];
     int ctr = 0;
     
     public Page CurrentPage
     {
        get { return page[ctr]; }
        set {
           // Move all the page objects down to accommodate the new one.
           if (ctr > page.GetUpperBound(0)) {
              for (int ndx = 1; ndx <= page.GetUpperBound(0); ndx++)
                 page[ndx - 1] = page[ndx];
           }    
           page[ctr] = value;
           if (ctr < page.GetUpperBound(0))
              ctr++; 
        }
     }
     
     public Page PreviousPage
     {
        get {
           if (ctr == 0) { 
              if (page[0] == null)
                 return null;
              else
                 return page[0];
           }
           else {
              ctr--;
              return page[ctr + 1];
           }
        }
     }         
  }
  
  public class Page
  {
     public Uri URL;
     public String Title;
  }
  // The example displays the following output:
  //    Unhandled Exception: 
  //       System.NullReferenceException: Object reference not set to an instance of an object.
  //       at Example.Main()
  

  Module Example
     Public Sub Main()
        Dim pages As New Pages()
        Dim title As String = pages.CurrentPage.Title
     End Sub
  End Module
  
  Public Class Pages 
     Dim page(9) As Page
     Dim ctr As Integer = 0
     
     Public Property CurrentPage As Page
        Get
           Return page(ctr)
        End Get
        Set
           ' Move all the page objects down to accommodate the new one.
           If ctr > page.GetUpperBound(0) Then
              For ndx As Integer = 1 To page.GetUpperBound(0)
                 page(ndx - 1) = page(ndx)
              Next
           End If    
           page(ctr) = value
           If ctr < page.GetUpperBound(0) Then ctr += 1 
        End Set
     End Property
     
     Public ReadOnly Property PreviousPage As Page
        Get
           If ctr = 0 Then 
              If page(0) Is Nothing Then
                 Return Nothing
              Else
                 Return page(0)
              End If   
           Else
              ctr -= 1
              Return page(ctr + 1)
           End If
        End Get
     End Property         
  End Class
  
  Public Class Page
     Public URL As Uri
     Public Title As String
  End Class
  ' The example displays the following output:
  '    Unhandled Exception: 
  '       System.NullReferenceException: Object reference not set to an instance of an object.
  '       at Example.Main()
  

  Se produce la excepción porque pages.CurrentPage devuelve null si no hay información de página se almacena en la memoria caché.The exception is thrown because pages.CurrentPage returns null if no page information is stored in the cache. Esta excepción puede corregirse mediante la comprobación del valor de la CurrentPage propiedad antes de recuperar actual Page del objeto Title propiedad, como en el ejemplo siguiente se hace:This exception can be corrected by testing the value of the CurrentPage property before retrieving the current Page object's Title property, as the following example does:

  using System;
  
  public class Example
  {
     public static void Main()
     {
        var pages = new Pages();
        Page current = pages.CurrentPage;
        if (current != null) {  
           String title = current.Title;
           Console.WriteLine("Current title: '{0}'", title);
        }
        else {
           Console.WriteLine("There is no page information in the cache.");
        }   
     }
  }
  // The example displays the following output:
  //       There is no page information in the cache.
  

  Module Example
     Public Sub Main()
        Dim pages As New Pages()
        Dim current As Page = pages.CurrentPage
        If current IsNot Nothing Then 
           Dim title As String = current.Title
           Console.WriteLine("Current title: '{0}'", title)
        Else
           Console.WriteLine("There is no page information in the cache.")
        End If   
     End Sub
  End Module
  ' The example displays the following output:
  '       There is no page information in the cache.
  

• Va a enumerar los elementos de una matriz que contiene los tipos de referencia y el intento de proceso se produce uno de los elementos un NullReferenceException excepción.You're enumerating the elements of an array that contains reference types, and your attempt to process one of the elements throws a NullReferenceException exception.

  El ejemplo siguiente define una matriz de cadenas.The following example defines a string array. Un for instrucción enumera los elementos de la matriz y llama a cada cadena Trim método antes de mostrar la cadena.A for statement enumerates the elements in the array and calls each string's Trim method before displaying the string.

  using System;
  
  public class Example
  {
     public static void Main()
     {
        String[] values = { "one", null, "two" };
        for (int ctr = 0; ctr <= values.GetUpperBound(0); ctr++)
           Console.Write("{0}{1}", values[ctr].Trim(), 
                         ctr == values.GetUpperBound(0) ? "" : ", "); 
        Console.WriteLine();
     }
  }
  // The example displays the following output:
  //    Unhandled Exception: 
  //       System.NullReferenceException: Object reference not set to an instance of an object.
  //       at Example.Main()
  

  Module Example
     Public Sub Main()
        Dim values() As String = { "one", Nothing, "two" }
        For ctr As Integer = 0 To values.GetUpperBound(0)
           Console.Write("{0}{1}", values(ctr).Trim(), 
                         If(ctr = values.GetUpperBound(0), "", ", ")) 
        Next
        Console.WriteLine()
     End Sub
  End Module
  ' The example displays the following output:
  '    Unhandled Exception: System.NullReferenceException: 
  '       Object reference not set to an instance of an object.
  '       at Example.Main()
  

  Esta excepción se produce si asume que cada elemento de la matriz debe contener un valor distinto de null y el valor del elemento de matriz es en realidad null.This exception occurs if you assume that each element of the array must contain a non-null value, and the value of the array element is in fact null. La excepción se puede eliminar mediante la comprobación de si el elemento es null antes de realizar cualquier operación en ese elemento, como en el ejemplo siguiente se muestra.The exception can be eliminated by testing whether the element is null before performing any operation on that element, as the following example shows.

  using System;
  
  public class Example
  {
     public static void Main()
     {
        String[] values = { "one", null, "two" };
        for (int ctr = 0; ctr <= values.GetUpperBound(0); ctr++)
           Console.Write("{0}{1}", 
                         values[ctr] != null ? values[ctr].Trim() : "", 
                         ctr == values.GetUpperBound(0) ? "" : ", "); 
        Console.WriteLine();
     }
  }
  // The example displays the following output:
  //       one, , two
  

  Module Example
     Public Sub Main()
        Dim values() As String = { "one", Nothing, "two" }
        For ctr As Integer = 0 To values.GetUpperBound(0)
           Console.Write("{0}{1}", 
                         If(values(ctr) IsNot Nothing, values(ctr).Trim(), ""), 
                         If(ctr = values.GetUpperBound(0), "", ", ")) 
        Next
        Console.WriteLine()
     End Sub
  End Module
  ' The example displays the following output:
  '       one, , two
  

• Un NullReferenceException se produce una excepción mediante un método que se pasa null.A NullReferenceException exception is thrown by a method that is passed null. Algunos métodos validan los argumentos que se les pasan.Some methods validate the arguments that are passed to them. Si lo hacen y uno de los argumentos es null, el método produce una System.ArgumentNullException excepción.If they do and one of the arguments is null, the method throws an System.ArgumentNullException exception. De lo contrario, produce una NullReferenceException excepción.Otherwise, it throws a NullReferenceException exception. El ejemplo siguiente muestra este escenario.The following example illustrates this scenario.

  using System;
  using System.Collections.Generic;
  
  public class Example
  {
     public static void Main()
     {
        List<String> names = GetData();
        PopulateNames(names);
     }
  
     private static void PopulateNames(List<String> names)
     {
        String[] arrNames = { "Dakota", "Samuel", "Nikita",
                              "Koani", "Saya", "Yiska", "Yumaevsky" };
        foreach (var arrName in arrNames)
           names.Add(arrName);
     }
     
     private static List<String> GetData() 
     {
        return null;   
     
     }
  }
  // The example displays output like the following:
  //    Unhandled Exception: System.NullReferenceException: Object reference 
  //    not set to an instance of an object.
  //       at Example.PopulateNames(List`1 names)
  //       at Example.Main()
  

  Imports System.Collections.Generic
  
  Module Example
     Public Sub Main()
        Dim names As List(Of String) = GetData()
        PopulateNames(names)
     End Sub
     
     Private Sub PopulateNames(names As List(Of String))
        Dim arrNames() As String = { "Dakota", "Samuel", "Nikita",
                                     "Koani", "Saya", "Yiska", "Yumaevsky" }
        For Each arrName In arrNames
           names.Add(arrName)
        Next
     End Sub
     
     Private Function GetData() As List(Of String)
        Return Nothing   
     End Function
  End Module
  ' The example displays output like the following:
  '    Unhandled Exception: System.NullReferenceException: Object reference 
  '    not set to an instance of an object.
  '       at Example.PopulateNames(List`1 names)
  '       at Example.Main()
  

  Para solucionar este problema, asegúrese de que no es el argumento pasado al método null, o controlar la excepción iniciada en un try…catch…finally bloque.To address this issue, make sure that the argument passed to the method is not null, or handle the thrown exception in a try…catch…finally block. Para obtener más información, consulta Excepciones.For more information, see Exceptions.

El siguiente generar instrucciones de lenguaje intermedio (MSIL) de Microsoft NullReferenceException: callvirt, cpblk, cpobj, initblk, ldelem.<type>, ldelema, ldfld, ldflda, ldind.<type> , ldlen, stelem.<type>, stfld, stind.<type>, throw, y unbox.The following Microsoft intermediate language (MSIL) instructions throw NullReferenceException: callvirt, cpblk, cpobj, initblk, ldelem.<type>, ldelema, ldfld, ldflda, ldind.<type>, ldlen, stelem.<type>, stfld, stind.<type>, throw, and unbox.

NullReferenceException utiliza HRESULT COR_E_NULLREFERENCE, que tiene el valor 0 x 80004003.NullReferenceException uses the HRESULT COR_E_NULLREFERENCE, which has the value 0x80004003.

Para obtener una lista de valores de propiedad iniciales de una instancia de NullReferenceException, consulte el NullReferenceException constructores.For a list of initial property values for an instance of NullReferenceException, see the NullReferenceException constructors.

Controlar excepciones NullReferenceException en código de versiónHandling NullReferenceException in release code

Es mejor evitar las excepciones NullReferenceException que controlara después de se produce.It's usually better to avoid a NullReferenceException than to handle it after it occurs. Controlar una excepción puede dificultar el mantenimiento y la comprensión del código y, a veces, puede introducir otros errores.Handling an exception can make your code harder to maintain and understand, and can sometimes introduce other bugs. Las excepciones NullReferenceException suelen ser errores sin recuperación.A NullReferenceException is often a non-recoverable error. En esos casos, la mejor opción puede ser permitir que la excepción detenga la aplicación.In these cases, letting the exception stop the app might be the best alternative.

Sin embargo, hay muchas situaciones en las que puede ser útil controlar el error:However, there are many situations where handling the error can be useful:

• La aplicación puede pasar por alto los objetos que son NULL.Your app can ignore objects that are null. Por ejemplo, si la aplicación recupera y procesa los registros de una base de datos, puede caber la opción de pasar por alto cierto número de registros incorrectos que generan objetos NULL.For example, if your app retrieves and processes records in a database, you might be able to ignore some number of bad records that result in null objects. Es posible que solo tenga que registrar los datos incorrectos en un archivo de registro o en la interfaz de usuario de la aplicación.Recording the bad data in a log file or in the application UI might be all you have to do.

• La recuperación tras la excepción es posible.You can recover from the exception. Por ejemplo, una llamada a un servicio web que devuelve un tipo de referencia podría devolver NULL si se interrumpe la conexión o se agota el tiempo de espera. Puede tratar de restablecer la conexión y volver a hacer la llamada.For example, a call to a web service that returns a reference type might return null if the connection is lost or the connection times out. You can attempt to reestablish the connection and try the call again.

• Puede restaurar el estado de la aplicación a un estado válido.You can restore the state of your app to a valid state. Por ejemplo, puede que esté realizando una tarea con varios pasos que exija guardar información en un almacén de datos antes de llamar a un método que lance una excepción NullReferenceException.For example, you might be performing a multi-step task that requires you to save information to a data store before you call a method that throws a NullReferenceException. Si el objeto sin inicializar fuera a dañar el registro de datos, puede quitar los datos anteriores antes de cerrar la aplicación.If the uninitialized object would corrupt the data record, you can remove the previous data before you close the app.

• La excepción se tiene que notificar.You want to report the exception. Por ejemplo, si la causa del error fue un error del usuario de la aplicación, puede generar un mensaje para indicarle cómo proporcionar la información correcta.For example, if the error was caused by a mistake from the user of your app, you can generate a message to help him supply the correct information. También puede registrar información sobre el error para facilitar la resolución del problema.You can also log information about the error to help you fix the problem. Algunos marcos, como ASP.NET, tienen un controlador de excepciones de nivel superior que captura todos los errores para que la aplicación no se bloquee nunca. En ese caso, puede que la única forma de saber que se produce sea registrar la excepción.Some frameworks, like ASP.NET, have a high-level exception handler that captures all errors to that the app never crashes; in that case, logging the exception might be the only way you can know that it occurs.

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Consulte también:

• Exception Exception Exception Exception
• Controlar y generar excepcionesHandling and Throwing Exceptions