OleDbConnectionStringBuilder.TryGetValue(String, Object) Method
Definition
Important
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Retrieves a value corresponding to the supplied key from the OleDbConnectionStringBuilder instance.
public:
override bool TryGetValue(System::String ^ keyword, [Runtime::InteropServices::Out] System::Object ^ % value);public override bool TryGetValue (string keyword, out object? value);public override bool TryGetValue (string keyword, out object value);override this.TryGetValue : string * obj -> boolPublic Overrides Function TryGetValue (keyword As String, ByRef value As Object) As BooleanParameters
- keyword
- String
The key of the item to retrieve.
- value
- Object
The value corresponding to keyword.
Returns
true if keyword was found within the connection string; otherwise, false.
Exceptions
keyword contains a null value (Nothing in Visual Basic).
Examples
The following example demonstrates the behavior of the TryGetValue method.
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
Remarks
The TryGetValue method lets developers safely retrieve a value from a OleDbConnectionStringBuilder without needing to verify that the supplied key name is a valid key name. Because TryGetValue does not raise an exception when you call it, passing in a nonexistent key, you do not have to look for a key before retrieving its value. Calling TryGetValue with a nonexistent key will place the value null (Nothing in Visual Basic) in the value parameter.
