OleDbConnectionStringBuilder.TryGetValue(String, Object) 方法

定義

命名空間:

System.Data.OleDb

組件:

System.Data.OleDb.dll

套件:

System.Data.OleDb v9.0.0

來源:

OleDbConnectionStringBuilder.cs

從 OleDbConnectionStringBuilder 執行個體擷取對應至所提供索引鍵的值。

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

參數

keyword

String

要擷取之項目的索引鍵。

value

Object

對應到 keyword 的值。

傳回

Boolean

如果在連接字串中找到 keyword，則為 true；否則為 false。

例外狀況

ArgumentNullException

keyword 包含 null 值 (在 Visual Basic 中為 Nothing)。

範例

下列範例示範 方法的行為 TryGetValue 。

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

備註

TryGetValue 方法可讓開發人員安全地從 OleDbConnectionStringBuilder 擷取值，而不需確認提供的索引鍵名稱是有效的索引鍵名稱。 因為 TryGetValue 當您呼叫它時不會引發例外狀況，所以傳入不存在的索引鍵時，您不需要在擷取其值之前先尋找索引鍵。 使用不存在的索引鍵呼叫 TryGetValue 會將 null 值放在 Nothing 參數的 Visual Basic () 中 value 。

另請參閱

• 連接字串產生器
• ADO.NET 中的連接字串