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System Namespace

Microsoft Silverlight will reach end of support after October 2021. Learn more.

The System namespace contains fundamental classes and base classes that define commonly-used value and reference data types, events and event handlers, interfaces, attributes, and processing exceptions.

Other classes provide services supporting data type conversion, method parameter manipulation, mathematics, remote and local program invocation, application environment management, and supervision of managed and unmanaged applications.

Classes

  Class Description
Public class AccessViolationException The exception that is thrown when there is an attempt to read or write protected memory.
Public class Activator Contains methods to create types of objects locally. This class cannot be inherited.
Public class AggregateException Represents one or more errors that occur during application execution.
Public class AppDomain Represents an application domain, which is an isolated environment where applications execute. This class cannot be inherited.
Public class AppDomainManager Provides a managed equivalent of an unmanaged host.
Public class AppDomainSetup Represents assembly binding information that can be added to an instance of AppDomain.
Public class AppDomainUnloadedException The exception that is thrown when an attempt is made to access an unloaded application domain.
Public class ArgumentException The exception that is thrown when one of the arguments provided to a method is not valid.
Public class ArgumentNullException The exception that is thrown when a null reference (Nothing in Visual Basic) is passed to a method that does not accept it as a valid argument.
Public class ArgumentOutOfRangeException The exception that is thrown when the value of an argument is outside the allowable range of values as defined by the invoked method.
Public class ArithmeticException The exception that is thrown for errors in an arithmetic, casting, or conversion operation.
Public class Array Provides methods for creating, manipulating, searching, and sorting arrays, thereby serving as the base class for all arrays in the common language runtime.
Public class ArrayTypeMismatchException The exception that is thrown when an attempt is made to store an element of the wrong type within an array.
Public class Attribute Represents the base class for custom attributes.
Public class AttributeUsageAttribute Specifies the usage of another attribute class. This class cannot be inherited.
Public class BadImageFormatException The exception that is thrown when the file image of a DLL or an executable program is invalid.
Public class BitConverter Converts base data types to an array of bytes, and an array of bytes to base data types.
Public class Buffer Manipulates arrays of primitive types.
Public class CannotUnloadAppDomainException The exception that is thrown when an attempt to unload an application domain fails.
Public class CLSCompliantAttribute Indicates whether a program element is compliant with the Common Language Specification (CLS). This class cannot be inherited.
Public class Console Infrastructure. Represents the standard input, output, and error streams for console applications. This class cannot be inherited.
Public class ContextMarshalException The exception that is thrown when an attempt to marshal an object across a context boundary fails.
Public class ContextStaticAttribute Obsolete. Indicates that the value of a static field is unique for a particular context.
Public class Convert Converts a base data type to another base data type.
Public class DataMisalignedException The exception that is thrown when a unit of data is read from or written to an address that is not a multiple of the data size. This class cannot be inherited.
Public class DBNull Represents a nonexistent value. This class cannot be inherited.
Public class Delegate Represents a delegate, which is a data structure that refers to a static method or to a class instance and an instance method of that class.
Public class DivideByZeroException The exception that is thrown when there is an attempt to divide an integral or decimal value by zero.
Public class DllNotFoundException The exception that is thrown when a DLL specified in a DLL import cannot be found.
Public class EntryPointNotFoundException The exception that is thrown when an attempt to load a class fails due to the absence of an entry method.
Public class Enum Provides the base class for enumerations.
Public class Environment Provides information about, and means to manipulate, the current environment and platform. This class cannot be inherited.
Public class EventArgs EventArgs is the base class for classes containing event data.
Public class Exception Represents errors that occur during application execution.
Public class ExecutionEngineException Obsolete. The exception that is thrown when there is an internal error in the execution engine of the common language runtime. This class cannot be inherited.
Public class FieldAccessException The exception that is thrown when there is an invalid attempt to access a private or protected field inside a class.
Public class FileStyleUriParser A customizable parser based on the File scheme.
Public class FlagsAttribute Indicates that an enumeration can be treated as a bit field; that is, a set of flags.
Public class FormatException The exception that is thrown when the format of an argument does not meet the parameter specifications of the invoked method.
Public class FtpStyleUriParser A customizable parser based on the File Transfer Protocol (FTP) scheme.
Public class GC Controls the system garbage collector, a service that automatically reclaims unused memory.
Public class GenericUriParser A customizable parser for a hierarchical URI.
Public class HttpStyleUriParser A customizable parser based on the HTTP scheme.
Public class IndexOutOfRangeException The exception that is thrown when an attempt is made to access an element of an array with an index that is outside the bounds of the array. This class cannot be inherited.
Public class InvalidCastException The exception that is thrown for invalid casting or explicit conversion.
Public class InvalidOperationException The exception that is thrown when a method call is invalid for the object's current state.
Public class InvalidProgramException The exception that is thrown when a program contains invalid Microsoft intermediate language (MSIL) or metadata. Generally this indicates a bug in the compiler that generated the program.
Public class InvalidTimeZoneException The exception that is thrown when time zone information is invalid.
Public class Lazy<T> Provides support for lazy initialization.
Public class Lazy<T, TMetadata> Provides an extension of the Lazy<T> class with support for metadata.
Public class Math Provides constants and static methods for trigonometric, logarithmic, and other common mathematical functions.
Public class MemberAccessException The exception that is thrown when an attempt to access a class member fails.
Public class MethodAccessException The exception that is thrown when there is an invalid attempt to access a private or protected method inside a class.
Public class MissingFieldException The exception that is thrown when there is an attempt to dynamically access a field that does not exist.
Public class MissingMemberException The exception that is thrown when there is an attempt to dynamically access a class member that does not exist.
Public class MissingMethodException The exception that is thrown when there is an attempt to dynamically access a method that does not exist.
Public class MulticastDelegate Represents a multicast delegate; that is, a delegate that can have more than one element in its invocation list.
Public class MulticastNotSupportedException The exception that is thrown when there is an attempt to combine two delegates based on the Delegate type instead of the MulticastDelegate type. This class cannot be inherited.
Public class NotFiniteNumberException The exception that is thrown when a floating-point value is positive infinity, negative infinity, or Not-a-Number (NaN).
Public class NotImplementedException The exception that is thrown when a requested method or operation is not implemented.
Public class NotSupportedException The exception that is thrown when an invoked method is not supported, or when there is an attempt to read, seek, or write to a stream that does not support the invoked functionality.
Public class Nullable Supports a value type that can be assigned nulla null reference (Nothing in Visual Basic) like a reference type. This class cannot be inherited.
Public class NullReferenceException The exception that is thrown when there is an attempt to dereference a null object reference.
Public class Object Supports all classes in the .NET Framework class hierarchy and provides low-level services to derived classes. This is the ultimate base class of all classes in the .NET Framework; it is the root of the type hierarchy.
Public class ObjectDisposedException The exception that is thrown when an operation is performed on a disposed object.
Public class ObsoleteAttribute Marks the program elements that are no longer in use. This class cannot be inherited.
Public class OperatingSystem Represents information about an operating system, such as the version and platform identifier. This class cannot be inherited.
Public class OperationCanceledException The exception that is thrown in a thread upon cancellation of an operation that the thread was executing.
Public class OutOfMemoryException The exception that is thrown when there is not enough memory to continue the execution of a program.
Public class OverflowException The exception that is thrown when an arithmetic, casting, or conversion operation in a checked context results in an overflow.
Public class ParamArrayAttribute Indicates that a method will allow a variable number of arguments in its invocation. This class cannot be inherited.
Public class PlatformNotSupportedException The exception that is thrown when a feature does not run on a particular platform.
Public class Random Represents a pseudo-random number generator, a device that produces a sequence of numbers that meet certain statistical requirements for randomness.
Public class RankException The exception that is thrown when an array with the wrong number of dimensions is passed to a method.
Public class ResolveEventArgs Provides data for the AppDomain.AssemblyResolve event.
Public class StackOverflowException The exception that is thrown when the execution stack overflows because it contains too many nested method calls. This class cannot be inherited.
Public class STAThreadAttribute Obsolete. Indicates that the COM threading model for an application is single-threaded apartment (STA).
Public class String Represents text as a series of Unicode characters.
Public class StringComparer Represents a string comparison operation that uses specific case and culture-based or ordinal comparison rules.
Public class SystemException Defines the base class for predefined exceptions in the System namespace.
Public class ThreadStaticAttribute Indicates that the value of a static field is unique for each thread.
Public class TimeoutException The exception that is thrown when the time allotted for a process or operation has expired.
Public class TimeZoneInfo Represents a time zone.
Public class Tuple Provides static methods for creating tuple objects.
Public class Tuple<T1> Represents a 1-tuple, or singleton.
Public class Tuple<T1, T2> Represents a 2-tuple, or pair.
Public class Tuple<T1, T2, T3> Represents a 3-tuple, or triple.
Public class Tuple<T1, T2, T3, T4> Represents a 4-tuple, or quadruple.
Public class Tuple<T1, T2, T3, T4, T5> Represents a 5-tuple, or quintuple.
Public class Tuple<T1, T2, T3, T4, T5, T6> Represents a 6-tuple, or sextuple.
Public class Tuple<T1, T2, T3, T4, T5, T6, T7> Represents a 7-tuple, or septuple.
Public class Tuple<T1, T2, T3, T4, T5, T6, T7, TRest> Represents an n-tuple, where n is 8 or greater.
Public class Type Represents type declarations: class types, interface types, array types, value types, enumeration types, type parameters, generic type definitions, and open or closed constructed generic types.
Public class TypeAccessException The exception that is thrown when a method attempts to use a type that it does not have access to.
Public class TypeInitializationException The exception that is thrown as a wrapper around the exception thrown by the class initializer. This class cannot be inherited.
Public class TypeLoadException The exception that is thrown when type-loading failures occur.
Public class UnauthorizedAccessException The exception that is thrown when the operating system denies access because of an I/O error or a specific type of security error.
Public class UnhandledExceptionEventArgs Provides data for the event that is raised when there is an exception that is not handled in any application domain.
Public class Uri Provides an object representation of a uniform resource identifier (URI) and easy access to the parts of the URI.
Public class UriBuilder Provides a custom constructor for uniform resource identifiers (URIs) and modifies URIs for the Uri class.
Public class UriFormatException The exception that is thrown when an invalid Uniform Resource Identifier (URI) is detected.
Public class UriParser Parses a new URI scheme. This is an abstract class.
Public class UriTemplate A class that represents a Uniform Resource Identifier (URI) template.
Public class UriTypeConverter Converts instances of the String type to Uri instances.
Public class ValueType Provides the base class for value types.
Public class Version Represents the version number of an assembly, operating system, or the common language runtime. This class cannot be inherited.
Public class WeakReference Represents a weak reference, which references an object while still allowing that object to be reclaimed by garbage collection.

Structures

  Structure Description
Public structure ArraySegment<T> Delimits a section of a one-dimensional array.
Public structure Boolean Represents a Boolean value.
Public structure Byte Represents an 8-bit unsigned integer.
Public structure Char Represents a Unicode character.
Public structure DateTime Represents an instant in time, typically expressed as a date and time of day.
Public structure DateTimeOffset Represents a point in time, typically expressed as a date and time of day, relative to Coordinated Universal Time (UTC).
Public structure Decimal Represents a decimal number.
Public structure Double Represents a double-precision floating-point number.
Public structure Guid Represents a globally unique identifier (GUID).
Public structure Int16 Represents a 16-bit signed integer.
Public structure Int32 Represents a 32-bit signed integer.
Public structure Int64 Represents a 64-bit signed integer.
Public structure IntPtr A platform-specific type that is used to represent a pointer or a handle.
Public structure Nullable<T> Represents an object whose underlying type is a value type that can also be assigned nulla null reference (Nothing in Visual Basic) like a reference type.
Public structure RuntimeArgumentHandle References a variable-length argument list.
Public structure RuntimeFieldHandle Represents a field using an internal metadata token.
Public structure RuntimeMethodHandle RuntimeMethodHandle is a handle to the internal metadata representation of a method.
Public structure RuntimeTypeHandle Represents a type using an internal metadata token.
Public structure SByte Represents an 8-bit signed integer.
Public structure Single Represents a single-precision floating-point number.
Public structure TimeSpan Represents a time interval.
Public structure TypedReference Describes objects that contain both a managed pointer to a location and a runtime representation of the type that may be stored at that location.
Public structure UInt16 Represents a 16-bit unsigned integer.
Public structure UInt32 Represents a 32-bit unsigned integer.
Public structure UInt64 Represents a 64-bit unsigned integer.
Public structure UIntPtr A platform-specific type that is used to represent a pointer or a handle.
Public structure Void Specifies a return value type for a method that does not return a value.

Interfaces

  Interface Description
Public interface IAsyncResult Represents the status of an asynchronous operation.
Public interface IComparable Defines a generalized type-specific comparison method that a value type or class implements to order or sort its instances.
Public interface IComparable<T> Defines a generalized comparison method that a value type or class implements to create a type-specific comparison method for ordering instances.
Public interface IConvertible Defines methods that convert the value of the implementing reference or value type to a common language runtime type that has an equivalent value.
Public interface ICustomFormatter Defines a method that supports custom, user-defined formatting of the value of an object.
Public interface IDisposable Defines a method to release allocated resources.
Public interface IEquatable<T> Defines a generalized method that a value type or class implements to create a type-specific method for determining equality of instances.
Public interface IFormatProvider Provides a mechanism for retrieving an object to control formatting.
Public interface IFormattable Provides functionality to format the value of an object into a string representation.
Public interface IServiceProvider Defines a mechanism for retrieving a service object; that is, an object that provides custom support to other objects.

Delegates

  Delegate Description
Public delegate Action Encapsulates a method that takes no parameters and does not return a value.
Public delegate Action<T> Encapsulates a method that takes a single parameter and does not return a value.
Public delegate Action<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10> Encapsulates a method that has 10 parameters and does not return a value.
Public delegate Action<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11> Encapsulates a method that has 11 parameters and does not return a value.
Public delegate Action<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12> Encapsulates a method that has 12 parameters and does not return a value.
Public delegate Action<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13> Encapsulates a method that has 13 parameters and does not return a value.
Public delegate Action<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14> Encapsulates a method that has 14 parameters and does not return a value.
Public delegate Action<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15> Encapsulates a method that has 15 parameters and does not return a value.
Public delegate Action<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16> Encapsulates a method that has 16 parameters and does not return a value.
Public delegate Action<T1, T2> Encapsulates a method that has two parameters and does not return a value.
Public delegate Action<T1, T2, T3> Encapsulates a method that takes three parameters and does not return a value.
Public delegate Action<T1, T2, T3, T4> Encapsulates a method that has four parameters and does not return a value.
Public delegate Action<T1, T2, T3, T4, T5> Encapsulates a method that has five parameters and does not return a value.
Public delegate Action<T1, T2, T3, T4, T5, T6> Encapsulates a method that has six parameters and does not return a value.
Public delegate Action<T1, T2, T3, T4, T5, T6, T7> Encapsulates a method that has seven parameters and does not return a value.
Public delegate Action<T1, T2, T3, T4, T5, T6, T7, T8> Encapsulates a method that has eight parameters and does not return a value.
Public delegate Action<T1, T2, T3, T4, T5, T6, T7, T8, T9> Encapsulates a method that has nine parameters and does not return a value.
Public delegate AsyncCallback References a method to be called when a corresponding asynchronous operation is completed.
Public delegate Comparison<T> Represents the method that compares two objects of the same type.
Public delegate Converter<TInput, TOutput> Represents a method that converts an object from one type to another type.
Public delegate EventHandler Represents the method that will handle an event that has no event data.
Public delegate EventHandler<TEventArgs> Represents the method that will handle an event.
Public delegate Func<TResult> Encapsulates a method that has no parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, TResult> Encapsulates a method that has nine parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, TResult> Encapsulates a method that has 10 parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, TResult> Encapsulates a method that has 11 parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, TResult> Encapsulates a method that has 12 parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, TResult> Encapsulates a method that has 13 parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, TResult> Encapsulates a method that has 14 parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, TResult> Encapsulates a method that has 15 parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, TResult> Encapsulates a method that has 16 parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T, TResult> Encapsulates a method that has one parameter and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, TResult> Encapsulates a method that has two parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, TResult> Encapsulates a method that has three parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, T4, TResult> Encapsulates a method that has four parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, T4, T5, TResult> Encapsulates a method that has five parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, T4, T5, T6, TResult> Encapsulates a method that has six parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, T4, T5, T6, T7, TResult> Encapsulates a method that has seven parameters and returns a value of the type specified by the TResult parameter.
Public delegate Func<T1, T2, T3, T4, T5, T6, T7, T8, TResult> Encapsulates a method that has eight parameters and returns a value of the type specified by the TResult parameter.
Public delegate Predicate<T> Represents the method that defines a set of criteria and determines whether the specified object meets those criteria.
Public delegate ResolveEventHandler Represents the method that handles the AppDomain.AssemblyResolve event.
Public delegate UnhandledExceptionEventHandler Represents the method that will handle the event raised by an exception that is not handled by the application domain.

Enumerations

  Enumeration Description
Public enumeration AttributeTargets Specifies the application elements on which it is valid to apply an attribute.
Public enumeration DateTimeKind Specifies whether a DateTime object represents a local time, a Coordinated Universal Time (UTC), or is not specified as either local time or UTC.
Public enumeration DayOfWeek Specifies the day of the week.
Public enumeration Environment.SpecialFolder When it is called by trusted applications, specifies enumerated constants used to retrieve directory paths to system special folders.
Public enumeration GenericUriParserOptions Specifies options for a UriParser.
Public enumeration LoaderOptimization An enumeration used to specify loader optimizations for an executable.
Public enumeration PlatformID Identifies the operating system, or development platform, supported by an assembly.
Public enumeration StringComparison Specifies the culture, case, and sort rules to be used by certain overloads of the String.Compare and String.Equals methods.
Public enumeration StringSplitOptions Specifies whether methods that split delimited substrings include or omit empty substrings from the returned array.
Public enumeration TypeCode Specifies the type of an object.
Public enumeration UriComponents Specifies the parts of a Uri.
Public enumeration UriFormat Controls how URI information is escaped.
Public enumeration UriIdnScope Provides the possible values for the configuration setting Internationalized Domain Name parsing.
Public enumeration UriKind Defines the kinds of Uris for several Uri.Uri methods.