DbConnectionStringBuilder.TryGetValue(String, Object) 方法
定义
重要
一些信息与预发行产品相关,相应产品在发行之前可能会进行重大修改。 对于此处提供的信息,Microsoft 不作任何明示或暗示的担保。
从此 DbConnectionStringBuilder 中检索与提供的键相对应的值。
public:
virtual bool TryGetValue(System::String ^ keyword, [Runtime::InteropServices::Out] System::Object ^ % value);
public virtual bool TryGetValue (string keyword, out 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
参数
- keyword
- String
要检索的项的键。
- value
- Object
与 keyword
对应的值。
返回
如果在连接字符串中找到 keyword
,则为 true
,否则为 false
。
例外
keyword
包含一个 null 值(在 Visual Basic 中为 Nothing
)。
示例
以下示例调用该方法 TryGetValue ,演示了多个可能的结果。
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
此示例显示以下结果:
Provider=sqloledb
DATA SOURCE=192.168.168.1,1433
Unable to retrieve value for //InvalidKey//
Unable to retrieve value for null key.
注解
此方法 TryGetValue 允许开发人员安全地从某个 DbConnectionStringBuilder 值检索值,而无需首先调用 ContainsKey 该方法。 由于 TryGetValue 在调用它时不引发异常,因此传入不存在的键时,无需在检索其值之前查找密钥。 使用不存在的键进行调用TryGetValue会将 null 值 (Nothing
置于参数Visual Basic) value
中。