IDisposable Interface
Provides a mechanism for releasing unmanaged resources.
To browse the .NET Framework source code for this type, see the Reference Source.
Assembly: mscorlib (in mscorlib.dll)
| Name | Description | |
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![]() | Dispose() | Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources. |
Note |
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To view the .NET Framework source code for this type, see the Reference Source. You can browse through the source code online, download the reference for offline viewing, and step through the sources (including patches and updates) during debugging; see instructions. |
The primary use of this interface is to release unmanaged resources. The garbage collector automatically releases the memory allocated to a managed object when that object is no longer used. However, it is not possible to predict when garbage collection will occur. Furthermore, the garbage collector has no knowledge of unmanaged resources such as window handles, or open files and streams.
Use the Dispose method of this interface to explicitly release unmanaged resources in conjunction with the garbage collector. The consumer of an object can call this method when the object is no longer needed.
Warning |
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It is a breaking change to add the IDisposable interface to an existing class. Because pre-existing consumers of your type cannot call Dispose, you cannot be certain that unmanaged resources held by your type will be released. |
Because the IDisposable.Dispose implementation is called by the consumer of a type when the resources owned by an instance are no longer needed, you should either wrap the managed object in a SafeHandle (the recommended alternative), or you should override Object.Finalize to free unmanaged resources in the event that the consumer forgets to call Dispose.
Important |
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In the .NET Framework, the C++ compiler supports deterministic disposal of resources and does not allow direct implementation of the Dispose method. |
For a detailed discussion about how this interface and the Object.Finalize method are used, see the Garbage Collection and Implementing a Dispose Method topics.
Implement IDisposable only if you are using unmanaged resources directly. If your app simply uses an object that implements IDisposable, don't provide an IDisposable implementation. Instead, you should call the object's IDisposable.Dispose implementation when you are finished using it. Depending on your programming language, you can do this in one of two ways:
By using a language construct such as the using statement in C# and Visual Basic.
By wrapping the call to the IDisposable.Dispose implementation in a try/catch block.
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Documentation for types that implement IDisposable note that fact and include a reminder to call its Dispose implementation. |
If your language supports a construct such as the using statement in C# and the Using statement in Visual Basic, you can use it instead of explicitly calling IDisposable.Dispose yourself. The following example uses this approach in defining a WordCount class that preserves information about a file and the number of words in it.
Imports System.IO Imports System.Text.RegularExpressions Public Class WordCount Private filename As String Private nWords As Integer Private pattern As String = "\b\w+\b" Public Sub New(filename As String) If Not File.Exists(filename) Then Throw New FileNotFoundException("The file does not exist.") End If Me.filename = filename Dim txt As String = String.Empty Using sr As New StreamReader(filename) txt = sr.ReadToEnd() End Using nWords = Regex.Matches(txt, pattern).Count End Sub Public ReadOnly Property FullName As String Get Return filename End Get End Property Public ReadOnly Property Name As String Get Return Path.GetFileName(filename) End Get End Property Public ReadOnly Property Count As Integer Get Return nWords End Get End Property End Class
The using statement is actually a syntactic convenience. At compile time, the language compiler implements the intermediate language (IL) for a try/catch block.
For more information about the using statement, see the Using Statement (Visual Basic) or using Statement (C# Reference) topics.
If your programming language does not support a construct like the using statement in C# or Visual Basic, or if you prefer not to use it, you can call the IDisposable.Dispose implementation from the finally block of a try/catch statement. The following example replaces the using block in the previous example with a try/catch/finally block.
Imports System.IO Imports System.Text.RegularExpressions Public Class WordCount Private filename As String Private nWords As Integer Private pattern As String = "\b\w+\b" Public Sub New(filename As String) If Not File.Exists(filename) Then Throw New FileNotFoundException("The file does not exist.") End If Me.filename = filename Dim txt As String = String.Empty Dim sr As StreamReader = Nothing Try sr = New StreamReader(filename) txt = sr.ReadToEnd() Finally If sr IsNot Nothing Then sr.Dispose() End Try nWords = Regex.Matches(txt, pattern).Count End Sub Public ReadOnly Property FullName As String Get Return filename End Get End Property Public ReadOnly Property Name As String Get Return Path.GetFileName(filename) End Get End Property Public ReadOnly Property Count As Integer Get Return nWords End Get End Property End Class
For more information about the try/finally pattern, see Try...Catch...Finally Statement (Visual Basic), try-finally (C# Reference), or try-finally Statement (C).
You should implement IDisposable only if your type uses unmanaged resources directly. The consumers of your type can call your IDisposable.Dispose implementation to free resources when the instance is no longer needed. To handle cases in which they fail to call Dispose, you should either use a class derived from SafeHandle to wrap the unmanaged resources, or you should override the Object.Finalize method for a reference type. In either case, you use the Dispose method to perform whatever cleanup is necessary after using the unmanaged resources, such as freeing, releasing, or resetting the unmanaged resources.
Important |
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If you are defining a base class that uses unmanaged resources and that either has, or is likely to have, subclasses that should be disposed, you should implement the IDisposable.Dispose method and provide a second overload of Dispose, as discussed in the next section. |
A base class with subclasses that should be disposable must implement IDisposable as follows. You should use this pattern whenever you implement IDisposable on any type that isn't sealed (NotInheritable in Visual Basic).
It should provide one public, non-virtual Dispose() method and a protected virtual Dispose(Boolean disposing) method.
The Dispose() method must call Dispose(true) and should suppress finalization for performance.
The base type should not include any finalizers.
The following code fragment reflects the dispose pattern for base classes. It assumes that your type does not override the Object.Finalize method.
Imports Microsoft.Win32.SafeHandles Imports System.Runtime.InteropServices Class BaseClass : Implements IDisposable ' Flag: Has Dispose already been called? Dim disposed As Boolean = False ' Instantiate a SafeHandle instance. Dim handle As SafeHandle = New SafeFileHandle(IntPtr.Zero, True) ' Public implementation of Dispose pattern callable by consumers. Public Sub Dispose() _ Implements IDisposable.Dispose Dispose(True) GC.SuppressFinalize(Me) End Sub ' Protected implementation of Dispose pattern. Protected Overridable Sub Dispose(disposing As Boolean) If disposed Then Return If disposing Then handle.Dispose() ' Free any other managed objects here. ' End If ' Free any unmanaged objects here. ' disposed = True End Sub End Class
If you do override the Object.Finalize method, your class should implement the following pattern.
Class BaseClass : Implements IDisposable ' Flag: Has Dispose already been called? Dim disposed As Boolean = False ' Public implementation of Dispose pattern callable by consumers. Public Sub Dispose() _ Implements IDisposable.Dispose Dispose(True) GC.SuppressFinalize(Me) End Sub ' Protected implementation of Dispose pattern. Protected Overridable Sub Dispose(disposing As Boolean) If disposed Then Return If disposing Then ' Free any other managed objects here. ' End If ' Free any unmanaged objects here. ' disposed = True End Sub Protected Overrides Sub Finalize() Dispose(False) End Sub End Class
Subclasses should implement the disposable pattern as follows:
They must override Dispose(Boolean) and call the base class Dispose(Boolean) implementation.
They can provide a finalizer if needed. The finalizer must call Dispose(false).
Note that derived classes do not themselves implement the IDisposable interface and do not include a parameterless Dispose method. They only override the base class Dispose(Boolean) method.
The following code fragment reflects the dispose pattern for derived classes. It assumes that your type does not override the Object.Finalize method.
Imports Microsoft.Win32.SafeHandles Imports System.Runtime.InteropServices Class DerivedClass : Inherits BaseClass ' Flag: Has Dispose already been called? Dim disposed As Boolean = False ' Instantiate a SafeHandle instance. Dim handle As SafeHandle = New SafeFileHandle(IntPtr.Zero, True) ' Protected implementation of Dispose pattern. Protected Overrides Sub Dispose(disposing As Boolean) If disposed Then Return If disposing Then handle.Dispose() ' Free any other managed objects here. ' End If ' Free any unmanaged objects here. ' disposed = True ' Call base class implementation. MyBase.Dispose(disposing) End Sub End Class
The following example demonstrates how to create a resource class that implements the IDisposable interface.
Imports System Imports System.ComponentModel ' The following example demonstrates how to create ' a resource class that implements the IDisposable interface ' and the IDisposable.Dispose method. Public Class DisposeExample ' A class that implements IDisposable. ' By implementing IDisposable, you are announcing that ' instances of this type allocate scarce resources. Public Class MyResource Implements IDisposable ' Pointer to an external unmanaged resource. Private handle As IntPtr ' Other managed resource this class uses. Private component As component ' Track whether Dispose has been called. Private disposed As Boolean = False ' The class constructor. Public Sub New(ByVal handle As IntPtr) Me.handle = handle End Sub ' Implement IDisposable. ' Do not make this method virtual. ' A derived class should not be able to override this method. Public Overloads Sub Dispose() Implements IDisposable.Dispose Dispose(True) ' This object will be cleaned up by the Dispose method. ' Therefore, you should call GC.SupressFinalize to ' take this object off the finalization queue ' and prevent finalization code for this object ' from executing a second time. GC.SuppressFinalize(Me) End Sub ' Dispose(bool disposing) executes in two distinct scenarios. ' If disposing equals true, the method has been called directly ' or indirectly by a user's code. Managed and unmanaged resources ' can be disposed. ' If disposing equals false, the method has been called by the ' runtime from inside the finalizer and you should not reference ' other objects. Only unmanaged resources can be disposed. Protected Overridable Overloads Sub Dispose(ByVal disposing As Boolean) ' Check to see if Dispose has already been called. If Not Me.disposed Then ' If disposing equals true, dispose all managed ' and unmanaged resources. If disposing Then ' Dispose managed resources. component.Dispose() End If ' Call the appropriate methods to clean up ' unmanaged resources here. ' If disposing is false, ' only the following code is executed. CloseHandle(handle) handle = IntPtr.Zero ' Note disposing has been done. disposed = True End If End Sub ' Use interop to call the method necessary ' to clean up the unmanaged resource. <System.Runtime.InteropServices.DllImport("Kernel32")> _ Private Shared Function CloseHandle(ByVal handle As IntPtr) As [Boolean] End Function ' This finalizer will run only if the Dispose method ' does not get called. ' It gives your base class the opportunity to finalize. ' Do not provide finalize methods in types derived from this class. Protected Overrides Sub Finalize() ' Do not re-create Dispose clean-up code here. ' Calling Dispose(false) is optimal in terms of ' readability and maintainability. Dispose(False) MyBase.Finalize() End Sub End Class Public Shared Sub Main() ' Insert code here to create ' and use the MyResource object. End Sub End Class
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1



