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.NET / C# Troubleshooting
The type or namespace name '<type-name>' could not be found (C#)
(or which namespace do I need for type <type-name>?)
Symptom:
When compiling a C# application the compiler generates the following error:
The type or namespace name 'TTTT' could not be found (are you missing a using directive or an assembly reference?)
where 'TTTT' is the name of a class.
If you are using VB.Net then the error is slightly different:
Type 'TTTT' is not defined.'
in this case please refer to the VB.Net version of this article "Type TTTT is not defined".
Cause:
The compiler does not recognise the class name 'TTTT'.
This is either because the class name is miss-spelt or because the compiler
could not find a corresponding definition.
Possible remedies:
- A common cause is a simple misspelling where the class name is used.
For example:
OdbcConection connection;
Here the class name should have been '
OdbcConnection', so the solution is to correct the spelling. - If the name refers to a component defined in the same project and then see my notes for "Type <component-name> is not defined".
- If the name is correct then the next most likely cause is that the
required namespace has not been included.
For example:
OdbcConnection connection;
.
.
The type or namespace name 'OdbcConnection' could not be found (are you missing a using directive or an assembly reference?)In this example 'OdbcConnection' is defined in the namespace 'System.Data.Odbc' (although this differs been the .Net framework 1.0 and later versions). Try importing the necessary namespace, so in this case:
using System.Data.Odbc;
Note that this "using" statement must be included at the very top of the file (i.e. before any code).
The following table (which is not exhaustive) lists .NET class names together with the namespace that defines them:
Name Namespace ArrayList System.Collections ASCIIEncoding System.Text BasicHttpBinding System.ServiceModel BasicHttpSecurity BinaryFormatter System.Runtime .Serialization .Formatters .Binary Bindable
as in <Bindable ...System.ComponentModel Bitmap System.Drawing Brush System.Drawing Button System.Web.UI.WebControls CheckBoxList System.Web.UI.WebControls Color System.Drawing ColorMatrix System.Drawing.Imaging ComboBox System.Windows.Forms CompositeControl System.Web.UI.WebControls ConcurrentBag System.Collections.Concurrent Control System.Web.UI ControlCollection System.Web.UI CultureInfo System.Globalization DataRow System.Data DataTable System.Data DateTime System DateTimeFormatInfo System.Globalization DefaultProperty
as in <DefaultProperty ...System.ComponentModel DefaultValue
as in <DefaultValue ...System.ComponentModel Description
as in <Description ...System.ComponentModel DescriptionAttribute System.ComponentModel DESCryptoServiceProvider System.Security.Cryptography Dictionary
as in Dictionary<T>System.Collections.Generic DialogResult System.Windows.Forms DictionaryEntry System.Collections DirectoryInfo System.IO DllImport System.Runtime.InteropServices EventLog System.Diagnostics EventLogInstaller System.Configuration.Install
Note: Project needs a reference to system.configuration.install.dllFieldInfo System.Reflection FileOutputStream Java.IO
Note: Project needs a reference to vjslib and server requires the Visual J# runtime.FileStream System.IO FolderNameEditor System.Windows.Forms.Design
Note: Project needs a reference to System.Design, which is included in the full .NET framework but not in the cut down .NET Framework Client Profile.Font System.Drawing FtpWebRequest System.Net FtpWebResponse System.Net Graphics System.Drawing GZipStream System.IO.Compression
From .NET 2.0HMACSHA1 System.Security.Cryptography HttpRequest System.Web HttpRuntime System.Web HttpSessionState System.Web.SessionState HttpStatusCode System.Net HtmlHead System.Web.UI.HtmlControls HtmlMeta System.Web.UI.HtmlControls HtmlTextWriter System.Web.UI HttpsTransportBindingElement System.ServiceModel.Channels HttpWebRequest System.Net HttpWebResponse System.Net HybridDictionary System.Collections.Specialized ICryptoTransform System.Security.Cryptography IEnumerator System.Collections IHTMLDocument2 MSHTML
Note: Project needs a reference to the Microsoft HTML Object Library.ImageAttributes System.Drawing.Imaging Imaging System.Drawing IPAddress System.Net IPEndPoint System.Net IPHostEntry System.Net ISerializable System.Runtime.Serialization List
as in List<T>System.Collections.Generic ListBox System.Web.UI.WebControls ListDictionary System.Collections.Specialized ListItemCollection System.Web.UI.WebControls LiteralControl System.Web.UI MailAddress System.Net.Mail MailMessage In .NET 1.1: System.Web.Mail
From .NET 2.0: System.Net.MailManagementScope System.Management
Note: Project needs a reference to System.Management.Match System.Text.RegularExpressions MatchCollection System.Text.RegularExpressions MethodBase System.Reflection MemoryStream System.IO Mutex System.Threading MutexSecurity System.Security.AccessControl NameValueCollection System.Collections.Specialized Nullable System OdbcConnection System.Data.Odbc OdbcDataReader System.Data.Odbc OleDbCommand System.Data.OleDb OleDbConnection System.Data.OleDb OpenFileDialog System.Windows.Forms PagesSection System.Web.Configuration ParameterDirection System.Data Pen System.Drawing Point System.Drawing PointF System.Drawing ProcessInfo System.Web ProcessStartInfo System.Diagnostics PropertyInfo System.Reflection ProviderException System.Configuration.Provider RC2CryptoServiceProvider System.Security.Cryptography Regex System.Text.RegularExpressions RegistryKey Microsoft.Win32 RijndaelManaged System.Security.Cryptography SafeFileHandle Microsoft.Win32.SafeHandles ScriptManager System.Web.UI SemaphoreSlim
From .NET 4.System.Threading SerializationInfo System.Runtime.Serialization Socket System.Net.Sockets SolidBrush System.Drawing SortedList
as in SortedList(<T>)System.Collections.Generic SpinLock
From .NET 4.System.Threading SqlCommand System.Data.SqlClient SqlConnection System.Data.SqlClient SqlTransaction System.Data.SqlClient SslPolicyErrors System.Net.Security StackFrame System.Diagnostics StackTrace System.Diagnostics STAThreadAttribute
as in <STAThreadAttribute ...System Stream System.IO StreamingContext System.Runtime.Serialization StreamReader System.IO StreamWriter System.IO StringBuilder System.Text StringCollection System.Collections.Specialized StringReader System.IO StringWriter System.IO StructLayout
as in <StructLayout ...System.Runtime.InteropServices SymmetricAlgorithm System.Security.Cryptography TcpClient System.Net.Sockets TextInfo System.Globalization TextReader System.IO Thread System.Threading ThreadPriority System.Threading ToolboxData
as in <... ToolboxData ...System.Web.UI TripleDES System.Security.Cryptography TripleDESCryptoServiceProvider System.Security.Cryptography UpdateCheckInfo System.Deployment.Application UpdatePanel System.Web.UI UTF8Encoding System.Text Unit System.Web.UI.WebControls WebClient System.Net WebControl System.Web.UI.WebControls WebRequest System.Net Win32Exception System.ComponentModel WindowsIdentity System.Security.Principal WindowsPrincipal System.Security.Principal X509Certificate System.Security.Cryptography .X509Certificates X509Chain System.Security.Cryptography .X509Certificates XmlDocument System.Xml XmlElement System.Xml XmlReader System.Xml XmlReaderSettings System.Xml XmlTextReader System.Xml XmlTextWriter System.Xml XslCompiledTransform System.Xml.Xsl ZipEntry Java.Util.Zip
Note: Project needs a reference to vjslib and server needs Visual J# runtime.ZipInputStream Java.Util.Zip
Note: Project needs a reference to vjslib and server needs Visual J# runtime.ZipOutputStream Java.Util.Zip
Note: Project needs a reference to vjslib and server needs Visual J# runtime.Zone System.Security.Policy I expect to add to this table over time.
- If the name is correct and the necessary namespace has been included then check the framework version. Not all classes and types are available for all frameworks. For example "SempahoreSlim" was introduced with the .Net framework 4, which means that you will get an error trying to use it if you are targeting a .NET framework earlier than the .NET 4 framework after including a reference to System.Threading.
These notes are believed to be correct for C# for .NET 1.1, .NET 2, .NET 3.5 and .NET 4, and may apply to other versions as well.
For the corresponding VB.Net version of this article please see "Type TTTT is not defined".