OdbcConnectionStringBuilder.TryGetValue(String, Object) 方法

定义

命名空间:

System.Data.Odbc

程序集:

System.Data.Odbc.dll

包:

System.Data.Odbc v8.0.0

Source:

OdbcConnectionStringbuilder.cs

从此 OdbcConnectionStringBuilder 中检索与提供的键相对应的值。

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

参数

keyword

String

要检索的项的键。

value

Object

与 keyword 对应的值。

返回

Boolean

如果在连接字符串中找到 keyword，则为 true；否则为 false。

示例

下面的示例演示 了 方法的行为 TryGetValue 。

using System.Data.Odbc;

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

        // Call TryGetValue method for multiple
        // key names. Demonstrate that the search is not
        // case sensitive.
        DisplayValue(builder, "Driver");
        DisplayValue(builder, "SERVER");
        // How about a property you did not set?
        DisplayValue(builder, "DNS");
        // Invalid keys?
        DisplayValue(builder, "Invalid Key");
        // Null values?
        DisplayValue(builder, null);

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

    private static 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 "Driver={SQL Server};Server=(local);" +
            "Database=AdventureWorks;Trusted_Connection=yes;";
    }

    private static void DisplayValue(OdbcConnectionStringBuilder 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 ex)
        {
            Console.WriteLine("Unable to retrieve value for null key.");
        }
    }
}

Imports System.Data.Odbc
    
Module Module1

  Sub Main()
    Dim builder As New OdbcConnectionStringBuilder
    builder.ConnectionString = GetConnectionString()

    ' Call TryGetValue method for multiple
    ' key names. Demonstrate that the search is not
    ' case sensitive.
    DisplayValue(builder, "Driver")
    DisplayValue(builder, "SERVER")
    ' How about a property you did not set?
    DisplayValue(builder, "DNS")
    ' 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 OdbcConnectionStringBuilder, 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 "Driver={SQL Server};Server=(local);" & _
      "Database=AdventureWorks;Trusted_Connection=yes;"
  End Function
End Module

注解

TryGetValue 方法允许开发人员安全地从 OdbcConnectionStringBuilder 中检索值，而无需验证提供的键名是否为有效的键名。 由于 TryGetValue 在传入不存在的键时不会引发异常，因此不必在检索键值之前查找密钥。 使用不存在的键调用 TryGetValue 会将值 null (Nothing 置于 Visual Basic) 参数中 value 。

另请参阅

• 连接字符串生成器
• ADO.NET 中的连接字符串