DbConnectionStringBuilder.TryGetValue(String, Object) 方法

定義

命名空間:
System.Data.Common
組件:
System.Data.Common.dll
組件:
System.Data.dll
組件:
netstandard.dll

從此 DbConnectionStringBuilder中取得對應所提供金鑰的值。

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

要取回物品的鑰匙。

value
Object

對應於的 keyword值。

傳回

Boolean

若< 連接字串 內發現 c1 />，則 。

例外狀況

ArgumentNullException

keyword 包含一個空值（Nothing 在 Visual Basic）。

範例

以下範例呼叫該 TryGetValue 方法，展示多種可能結果。

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 = "..."

    ' 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

樣本顯示以下結果：

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

備註

此TryGetValue方法讓開發者無需先呼叫該ContainsKey方法，就能安全地從 a DbConnectionStringBuilder 取得值。 因為 TryGetValue 當你呼叫它時不會觸發例外，傳遞一個不存在的金鑰，所以你不必在取得金鑰值前尋找它。 若呼叫 TryGetValue 並使用不存在的鍵，空值（Nothing 在 Visual Basic 中）會放在 value 參數中。

適用於

另請參閱