DbConnectionStringBuilder.TryGetValue(String, Object) 方法

定義

命名空間:

System.Data.Common

組件:

System.Data.Common.dll

來源:

DbConnectionStringBuilder.cs

從這個 DbConnectionStringBuilder 擷取對應到所提供之索引鍵的值。

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

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

abstract member TryGetValue : string * obj -> bool
override this.TryGetValue : string * obj -> bool

Public Overridable 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

對應至 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

下列範例會呼叫 TryGetValue 方法，示範數個可能的結果。

static void Main()
{
    DbConnectionStringBuilder builder = new DbConnectionStringBuilder();
    builder.ConnectionString =
        "Provider=sqloledb;Data Source=192.168.168.1,1433;" +
        "Network Library=DBMSSOCN;Initial Catalog=pubs;" +
        "Integrated Security=SSPI;";

    // Call TryGetValue method for multiple
    // key names.
    DisplayValue(builder, "Provider");
    DisplayValue(builder, "DATA SOURCE");
    DisplayValue(builder, "InvalidKey");
    DisplayValue(builder, null);

    Console.ReadLine();
}

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

    // Although TryGetValue handles missing keys,
    // it doesn't handle passing in a null
    // key. This example traps for that particular error, but
    // bubbles 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.");
    }
}

Sub Main()
    Dim builder As New DbConnectionStringBuilder
    builder.ConnectionString = _
        "Provider=sqloledb;Data Source=192.168.168.1,1433;" & _
        "Network Library=DBMSSOCN;Initial Catalog=pubs;" & _
        "Integrated Security=SSPI;"

    ' Call TryGetValue method for multiple
    ' key names.
    DisplayValue(builder, "Provider")
    DisplayValue(builder, "DATA SOURCE")
    DisplayValue(builder, "InvalidKey")
    DisplayValue(builder, Nothing)

    Console.ReadLine()
End Sub

Private Sub DisplayValue( _
 ByVal builder As DbConnectionStringBuilder, ByVal key As String)
    Dim value As Object

    ' Although TryGetValue handles missing keys,
    ' it doesn't handle passing in a null (Nothing in Visual Basic)
    ' key. This example traps for that particular error, but
    ' bubbles 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

此範例會顯示下列結果：

Provider=sqloledb
DATA SOURCE=192.168.168.1,1433
Unable to retrieve value for //InvalidKey//
Unable to retrieve value for null key.

備註

方法 TryGetValue 可讓開發人員安全地從 擷取值， DbConnectionStringBuilder 而不需要先呼叫 ContainsKey 方法。 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尋找索引鍵。 使用不存在的索引鍵呼叫 TryGetValue 會將 null 值 (放在 Nothing Visual Basic) 參數中 value 。

另請參閱

• ADO.NET 中的連接字串
• ADO.NET 概觀 \(部分機器翻譯\)