OleDbConnectionStringBuilder.TryGetValue(String, Object) Método

Definición

Espacio de nombres:

System.Data.OleDb

Ensamblado:

System.Data.OleDb.dll

Paquete:

System.Data.OleDb v9.0.0-rc.2.24473.5

Recupera un valor correspondiente a la clave proporcionada de la instancia de OleDbConnectionStringBuilder.

public:
 override bool TryGetValue(System::String ^ keyword, [Runtime::InteropServices::Out] System::Object ^ % value);

public override bool TryGetValue (string keyword, out object? value);

override this.TryGetValue : string * obj -> bool

Public Overrides Function TryGetValue (keyword As String, ByRef value As Object) As Boolean

Parámetros

keyword

String

Clave del elemento que se va a recuperar.

value

Object

Valor que corresponde a keyword.

Devoluciones

Boolean

Es true si keyword fue encontrado dentro de la cadena de conexión, en caso contrario, es false.

Excepciones

ArgumentNullException

keyword contiene un valor null (Nothing en Visual Basic).

Ejemplos

En el ejemplo siguiente se muestra el comportamiento del TryGetValue método .

using System.Data.OleDb;

class Program
{
    static void Main()
    {
        OleDbConnectionStringBuilder builder =
            new OleDbConnectionStringBuilder();
        builder.ConnectionString = GetConnectionString();

        // Call TryGetValue method for multiple
        // key names.
        DisplayValue(builder, "Data Source");
        DisplayValue(builder, "Extended Properties");
        // How about implicitly added key/value pairs?
        DisplayValue(builder, "Jet OLEDB:System database");
        // Invalid keys?
        DisplayValue(builder, "Invalid Key");
        // Null values?
        DisplayValue(builder, null);

        Console.WriteLine("Press any key to continue.");
        Console.ReadLine();
    }

    static private void DisplayValue(OleDbConnectionStringBuilder builder, string key)
    {
        object value = null;

        // Although TryGetValue handles missing keys,
        // it does not handle passing in a null (Nothing in Visual Basic)
        // key. This example traps for that particular error, but
        // throws any other unknown exceptions back out to the
        // caller.
        try
        {
            if (builder.TryGetValue(key, out value))
            {
                Console.WriteLine("{0}='{1}'", key, value);
            }
            else
            {
                Console.WriteLine("Unable to retrieve value for '{0}'", key);
            }
        }
        catch (ArgumentNullException)
        {
            Console.WriteLine("Unable to retrieve value for null key.");
        }
    }

    static private string GetConnectionString()
    {
        // To avoid storing the connection string in your code,
        // you can retrieve it from a configuration file using the
        // System.Configuration.ConfigurationSettings.AppSettings property.
        return "Provider=Microsoft.Jet.OLEDB.4.0;" +
            "Data Source=C:\\ExcelDemo.xls;" +
            "Extended Properties=\"Excel 8.0;HDR=Yes;IMEX=1\"";
    }
}

Imports System.Data.OleDb    

Module Module1
  Sub Main()
    Dim builder As New OleDbConnectionStringBuilder
    builder.ConnectionString = GetConnectionString()

    ' Call TryGetValue method for multiple
    ' key names. 
    DisplayValue(builder, "Data Source")
    DisplayValue(builder, "Extended Properties")
    ' How about implicitly added key/value pairs?
    DisplayValue(builder, "Jet OLEDB:System database")
    ' Invalid keys?
    DisplayValue(builder, "Invalid Key")
    ' Null values?
    DisplayValue(builder, Nothing)

    Console.WriteLine("Press any key to continue.")
    Console.ReadLine()
  End Sub

  Private Sub DisplayValue( _
   ByVal builder As OleDbConnectionStringBuilder, ByVal key As String)
    Dim value As Object = Nothing

    ' Although TryGetValue handles missing keys,
    ' it does not handle passing in a null (Nothing in Visual Basic)
    ' key. This example traps for that particular error, but
    ' throws any other unknown exceptions back out to the
    ' caller. 
    Try
      If builder.TryGetValue(key, value) Then
        Console.WriteLine("{0}='{1}'", key, value)
      Else
        Console.WriteLine("Unable to retrieve value for '{0}'", key)
      End If
    Catch ex As ArgumentNullException
      Console.WriteLine("Unable to retrieve value for null key.")
    End Try
  End Sub

  Private Function GetConnectionString() As String
    ' To avoid storing the connection string in your code,
    ' you can retrieve it from a configuration file using the 
    ' System.Configuration.ConfigurationSettings.AppSettings property. 
    Return "Provider=Microsoft.Jet.OLEDB.4.0;" & _
      "Data Source=C:\ExcelDemo.xls;" & _
      "Extended Properties=""Excel 8.0;HDR=Yes;IMEX=1"""
  End Function
End Module

Comentarios

El método TryGetValue permite a los programadores recuperar de manera segura un valor de OleDbConnectionStringBuilder sin tener que comprobar si el nombre de clave proporcionado es válido. Dado TryGetValue que no genera una excepción al llamarla, pasar una clave inexistente, no es necesario buscar una clave antes de recuperar su valor. La llamada a TryGetValue con una clave inexistente colocará el valor NULL (Nothing en Visual Basic) en el value parámetro .

Consulte también

• Generadores de cadenas de conexión
• Cadenas de conexión de ADO.NET