本文提供此 API 參考文件的補充備註。
方法 Finalize 用於在物件被銷毀之前，對目前物件所持有的非受控資源執行清理作業。 方法受到保護，因此只能透過這個類別或衍生類別來存取。
最終處理的運作方式
類別 Object 不提供 Finalize 方法的實作，而且垃圾收集器不會標記衍生自 Object 的型別進行最終處理，除非它們覆寫 Finalize 方法。
如果類型確實覆寫 Finalize 方法，垃圾收集器會在內部結構中為該類型的每個實例新增一個項目，稱為最終化佇列。 最終處理佇列包含受管理堆積中所有物件的項目，這些項目的最終處理程式碼必須在垃圾收集器回收記憶體之前執行。 垃圾收集器接著會在下列情況下自動呼叫 Finalize 方法：
- 在垃圾回收器發現物件無法存取之後，除非透過呼叫GC.SuppressFinalize方法讓該物件豁免完成。
- 僅限在 .NET Framework 上，在應用程式域關閉期間，如果物件未豁免最終化。 在關機期間，即使是仍可存取的物件也會完成。
Finalize 只會在給定的實例上自動呼叫一次，除非透過像 GC.ReRegisterForFinalize 這樣的機制重新註冊物件，並且在此之後尚未呼叫 GC.SuppressFinalize 方法。
Finalize 工作有下列限制：
- 完成項執行的確切時間未定義。 若要確保類別實例的資源具決定性釋放，請實
Close作 方法或提供實 IDisposable.Dispose 作。 - 即使一個對象參考另一個物件，兩個物件的完成項不保證會以任何特定順序執行。 也就是說，如果物件 A 具有物件 B 的參考，而且兩者都有完成項，物件 B 在物件 A 的完成項啟動時可能已經完成。
- 終結器執行的線程未指定。
在下列例外情況下，Finalize 方法可能無法完成執行，甚至可能完全不執行：
- 如果另一個終結器無限期阻塞（進入無限迴圈，嘗試取得它永遠無法取得的鎖定，等等）。 由於執行階段會嘗試將終結器執行至完成，如果有終結器無限期阻塞，則其他終結器可能不會被呼叫。
- 如果進程終止而不讓執行期有機會進行清理。 在此情況下，運行時間的第一個進程終止通知是DLL_PROCESS_DETACH通知。
運行時間只會在關機期間繼續完成對象，同時可完成的物件數目會繼續減少。
如果 Finalize 或是 Finalize 的覆寫拋出例外，且執行環境不是由覆寫預設原則的應用程式所承載，則執行環境會終止流程，而且不會執行活躍 try/finally 中的區塊或完成項。 如果終結器無法釋放或銷毀資源，此行為能確保流程的完整性。
覆寫 Finalize 方法
您應該覆寫 Finalize 這個使用未受管理資源的類別，例如檔案句柄或資料庫連接。這些資源必須在垃圾收集期間，當使用它們的受管理物件被棄置時釋放。 您不應該為受管理物件實現 Finalize 方法，因為垃圾收集器會自動釋放受管理資源。
這很重要
如果有SafeHandle物件可包裝您的非受控資源，建議的替代方案是使用安全句柄來實作處置模式，而不是覆寫Finalize。 如需詳細資訊，請參閱 SafeHandle 選項 區段。
Object.Finalize方法預設不會執行任何動作，應僅在必要時覆寫 Finalize，並僅用於釋放未管理的資源。 記憶體回收的時間通常會更長，尤其是在執行終結操作的情況下，因為這需要至少兩次垃圾收集。 此外，您應該只覆寫 Finalize 參考型別的 方法。 Common Language Runtime 只會完成參考類型。 它會忽略值型別的析構函數。
Object.Finalize 方法的範圍是 protected。 當您覆寫 類別中的 方法時，應該維持這個有限的範圍。 藉由保護 Finalize 方法，您可以防止應用程式的使用者直接呼叫物件的 Finalize 方法。
衍生型別中每個對Finalize的實作都必須呼叫其基底型別的Finalize實作。 這是唯一允許應用程式程式代碼呼叫 Finalize的情況。 物件 Finalize 的方法不應該在其基類以外的任何物件上呼叫 方法。 由於在 Common Language Runtime 關閉時，其他被呼叫的物件可能會與呼叫物件同時被回收。
備註
C# 編譯程式不允許覆寫 Finalize 方法。 相反，您可以透過為類別實作一個 解構函式 來提供一個終結器。 C# 的解構函數會自動呼叫其基底類別的解構函數。
Visual C++也提供自己的語法來實作 Finalize 方法。 如需詳細資訊，請參閱 如何：定義和使用類別和結構（C++/CLI）中的「解構函數與終結器」一節。
因為垃圾回收是不具決定性的，因此您不知道垃圾回收器何時執行最終處理。 若要立即釋放資源，您也可以選擇實作 處置模式 和 IDisposable 介面。 您的類別使用者可以呼叫 IDisposable.Dispose 實作方法來釋放非受控資源，而在未呼叫 Finalize 方法的情況下，您可以使用 Dispose 方法來釋放非受控資源。
Finalize 幾乎可以採取任何動作，包括在垃圾收集期間清除對象後讓物件「復活」（即再次使物件可存取）。 不過，物件只能復活一次；Finalize 無法在垃圾收集期間呼叫於復活過的物件上。
SafeHandle 替代專案
建立可靠的完成項通常很困難，因為您無法假設應用程式的狀態，而且因為未處理的系統例外狀況，例如 OutOfMemoryException 和 StackOverflowException 終止完成項。 相較於實作終結器來釋放非受管理資源，您可以使用衍生自 System.Runtime.InteropServices.SafeHandle 類別的物件來包裝這些資源，然後實作不含終結器的處置模式。 .NET Framework 會在 衍生自 Microsoft.Win32的System.Runtime.InteropServices.SafeHandle命名空間中提供下列類別：
- SafeFileHandle 是檔句柄的包裝函式類別。
- SafeMemoryMappedFileHandle 是記憶體對應檔控制碼的包裝類別。
- SafeMemoryMappedViewHandle 是一個用於封裝非托管記憶體區塊指標的類別。
- SafeNCryptKeyHandle、 SafeNCryptProviderHandle和 SafeNCryptSecretHandle 是密碼編譯句柄的包裝函式類別。
- SafePipeHandle 是管道句柄的包裝函式類別。
- SafeRegistryHandle 是一個用於控制登錄機碼的包裝類。
- SafeWaitHandle 是等候句柄的包裝函式類別。
下列範例會使用 處置模式 搭配安全控制代碼，而不是覆寫 Finalize 方法。 它會定義類別 FileAssociation ，這個類別會包裝處理具有特定擴展名之檔案之應用程式的登錄資訊。 Windows out 函式呼叫時，傳回為參數的兩個註冊表控制碼會傳遞至建構SafeRegistryHandle函式。 然後，類型的受保護 Dispose 方法會呼叫 SafeRegistryHandle.Dispose 方法來釋放這兩個句柄。
using Microsoft.Win32.SafeHandles;
using System;
using System.ComponentModel;
using System.IO;
using System.Runtime.InteropServices;
public class FileAssociationInfo : IDisposable
{
// Private variables.
private String ext;
private String openCmd;
private String args;
private SafeRegistryHandle hExtHandle, hAppIdHandle;
// Windows API calls.
[DllImport("advapi32.dll", CharSet= CharSet.Auto, SetLastError=true)]
private static extern int RegOpenKeyEx(IntPtr hKey,
String lpSubKey, int ulOptions, int samDesired,
out IntPtr phkResult);
[DllImport("advapi32.dll", CharSet= CharSet.Unicode, EntryPoint = "RegQueryValueExW",
SetLastError=true)]
private static extern int RegQueryValueEx(IntPtr hKey,
string lpValueName, int lpReserved, out uint lpType,
string lpData, ref uint lpcbData);
[DllImport("advapi32.dll", SetLastError = true)]
private static extern int RegSetValueEx(IntPtr hKey, [MarshalAs(UnmanagedType.LPStr)] string lpValueName,
int Reserved, uint dwType, [MarshalAs(UnmanagedType.LPStr)] string lpData,
int cpData);
[DllImport("advapi32.dll", SetLastError=true)]
private static extern int RegCloseKey(UIntPtr hKey);
// Windows API constants.
private const int HKEY_CLASSES_ROOT = unchecked((int) 0x80000000);
private const int ERROR_SUCCESS = 0;
private const int KEY_QUERY_VALUE = 1;
private const int KEY_SET_VALUE = 0x2;
private const uint REG_SZ = 1;
private const int MAX_PATH = 260;
public FileAssociationInfo(String fileExtension)
{
int retVal = 0;
uint lpType = 0;
if (!fileExtension.StartsWith("."))
fileExtension = "." + fileExtension;
ext = fileExtension;
IntPtr hExtension = IntPtr.Zero;
// Get the file extension value.
retVal = RegOpenKeyEx(new IntPtr(HKEY_CLASSES_ROOT), fileExtension, 0, KEY_QUERY_VALUE, out hExtension);
if (retVal != ERROR_SUCCESS)
throw new Win32Exception(retVal);
// Instantiate the first SafeRegistryHandle.
hExtHandle = new SafeRegistryHandle(hExtension, true);
string appId = new string(' ', MAX_PATH);
uint appIdLength = (uint) appId.Length;
retVal = RegQueryValueEx(hExtHandle.DangerousGetHandle(), String.Empty, 0, out lpType, appId, ref appIdLength);
if (retVal != ERROR_SUCCESS)
throw new Win32Exception(retVal);
// We no longer need the hExtension handle.
hExtHandle.Dispose();
// Determine the number of characters without the terminating null.
appId = appId.Substring(0, (int) appIdLength / 2 - 1) + @"\shell\open\Command";
// Open the application identifier key.
string exeName = new string(' ', MAX_PATH);
uint exeNameLength = (uint) exeName.Length;
IntPtr hAppId;
retVal = RegOpenKeyEx(new IntPtr(HKEY_CLASSES_ROOT), appId, 0, KEY_QUERY_VALUE | KEY_SET_VALUE,
out hAppId);
if (retVal != ERROR_SUCCESS)
throw new Win32Exception(retVal);
// Instantiate the second SafeRegistryHandle.
hAppIdHandle = new SafeRegistryHandle(hAppId, true);
// Get the executable name for this file type.
string exePath = new string(' ', MAX_PATH);
uint exePathLength = (uint) exePath.Length;
retVal = RegQueryValueEx(hAppIdHandle.DangerousGetHandle(), String.Empty, 0, out lpType, exePath, ref exePathLength);
if (retVal != ERROR_SUCCESS)
throw new Win32Exception(retVal);
// Determine the number of characters without the terminating null.
exePath = exePath.Substring(0, (int) exePathLength / 2 - 1);
// Remove any environment strings.
exePath = Environment.ExpandEnvironmentVariables(exePath);
int position = exePath.IndexOf('%');
if (position >= 0) {
args = exePath.Substring(position);
// Remove command line parameters ('%0', etc.).
exePath = exePath.Substring(0, position).Trim();
}
openCmd = exePath;
}
public String Extension
{ get { return ext; } }
public String Open
{ get { return openCmd; }
set {
if (hAppIdHandle.IsInvalid | hAppIdHandle.IsClosed)
throw new InvalidOperationException("Cannot write to registry key.");
if (! File.Exists(value)) {
string message = String.Format("'{0}' does not exist", value);
throw new FileNotFoundException(message);
}
string cmd = value + " %1";
int retVal = RegSetValueEx(hAppIdHandle.DangerousGetHandle(), String.Empty, 0,
REG_SZ, value, value.Length + 1);
if (retVal != ERROR_SUCCESS)
throw new Win32Exception(retVal);
} }
public void Dispose()
{
Dispose(disposing: true);
GC.SuppressFinalize(this);
}
protected void Dispose(bool disposing)
{
// Ordinarily, we release unmanaged resources here;
// but all are wrapped by safe handles.
// Release disposable objects.
if (disposing) {
if (hExtHandle != null) hExtHandle.Dispose();
if (hAppIdHandle != null) hAppIdHandle.Dispose();
}
}
}
open Microsoft.Win32.SafeHandles
open System
open System.ComponentModel
open System.IO
open System.Runtime.InteropServices
// Windows API constants.
let HKEY_CLASSES_ROOT = 0x80000000
let ERROR_SUCCESS = 0
let KEY_QUERY_VALUE = 1
let KEY_SET_VALUE = 0x2
let REG_SZ = 1u
let MAX_PATH = 260
// Windows API calls.
[<DllImport("advapi32.dll", CharSet= CharSet.Auto, SetLastError=true)>]
extern int RegOpenKeyEx(nativeint hKey, string lpSubKey, int ulOptions, int samDesired, nativeint& phkResult)
[<DllImport("advapi32.dll", CharSet= CharSet.Unicode, EntryPoint = "RegQueryValueExW", SetLastError=true)>]
extern int RegQueryValueEx(nativeint hKey, string lpValueName, int lpReserved, uint& lpType, string lpData, uint& lpcbData)
[<DllImport("advapi32.dll", SetLastError = true)>]
extern int RegSetValueEx(nativeint hKey, [<MarshalAs(UnmanagedType.LPStr)>] string lpValueName, int Reserved, uint dwType, [<MarshalAs(UnmanagedType.LPStr)>] string lpData, int cpData)
[<DllImport("advapi32.dll", SetLastError=true)>]
extern int RegCloseKey(unativeint hKey)
type FileAssociationInfo(fileExtension: string) =
// Private values.
let ext =
if fileExtension.StartsWith "." |> not then
"." + fileExtension
else
fileExtension
let mutable args = ""
let mutable hAppIdHandle = Unchecked.defaultof<SafeRegistryHandle>
let mutable hExtHandle = Unchecked.defaultof<SafeRegistryHandle>
let openCmd =
let mutable lpType = 0u
let mutable hExtension = 0n
// Get the file extension value.
let retVal = RegOpenKeyEx(nativeint HKEY_CLASSES_ROOT, fileExtension, 0, KEY_QUERY_VALUE, &hExtension)
if retVal <> ERROR_SUCCESS then
raise (Win32Exception retVal)
// Instantiate the first SafeRegistryHandle.
hExtHandle <- new SafeRegistryHandle(hExtension, true)
let appId = String(' ', MAX_PATH)
let mutable appIdLength = uint appId.Length
let retVal = RegQueryValueEx(hExtHandle.DangerousGetHandle(), String.Empty, 0, &lpType, appId, &appIdLength)
if retVal <> ERROR_SUCCESS then
raise (Win32Exception retVal)
// We no longer need the hExtension handle.
hExtHandle.Dispose()
// Determine the number of characters without the terminating null.
let appId = appId.Substring(0, int appIdLength / 2 - 1) + @"\shell\open\Command"
// Open the application identifier key.
let exeName = String(' ', MAX_PATH)
let exeNameLength = uint exeName.Length
let mutable hAppId = 0n
let retVal = RegOpenKeyEx(nativeint HKEY_CLASSES_ROOT, appId, 0, KEY_QUERY_VALUE ||| KEY_SET_VALUE, &hAppId)
if retVal <> ERROR_SUCCESS then
raise (Win32Exception retVal)
// Instantiate the second SafeRegistryHandle.
hAppIdHandle <- new SafeRegistryHandle(hAppId, true)
// Get the executable name for this file type.
let exePath = String(' ', MAX_PATH)
let mutable exePathLength = uint exePath.Length
let retVal = RegQueryValueEx(hAppIdHandle.DangerousGetHandle(), String.Empty, 0, &lpType, exePath, &exePathLength)
if retVal <> ERROR_SUCCESS then
raise (Win32Exception retVal)
// Determine the number of characters without the terminating null.
let exePath =
exePath.Substring(0, int exePathLength / 2 - 1)
// Remove any environment strings.
|> Environment.ExpandEnvironmentVariables
let position = exePath.IndexOf '%'
if position >= 0 then
args <- exePath.Substring position
// Remove command line parameters ('%0', etc.).
exePath.Substring(0, position).Trim()
else
exePath
member _.Extension =
ext
member _.Open
with get () = openCmd
and set (value) =
if hAppIdHandle.IsInvalid || hAppIdHandle.IsClosed then
raise (InvalidOperationException "Cannot write to registry key.")
if not (File.Exists value) then
raise (FileNotFoundException $"'{value}' does not exist")
let cmd = value + " %1"
let retVal = RegSetValueEx(hAppIdHandle.DangerousGetHandle(), String.Empty, 0, REG_SZ, value, value.Length + 1)
if retVal <> ERROR_SUCCESS then
raise (Win32Exception retVal)
member this.Dispose() =
this.Dispose true
GC.SuppressFinalize this
member _.Dispose(disposing) =
// Ordinarily, we release unmanaged resources here
// but all are wrapped by safe handles.
// Release disposable objects.
if disposing then
if hExtHandle <> null then hExtHandle.Dispose()
if hAppIdHandle <> null then hAppIdHandle.Dispose()
interface IDisposable with
member this.Dispose() =
this.Dispose()
Imports Microsoft.Win32.SafeHandles
Imports System.ComponentModel
Imports System.IO
Imports System.Runtime.InteropServices
Imports System.Text
Public Class FileAssociationInfo : Implements IDisposable
' Private variables.
Private ext As String
Private openCmd As String
Private args As String
Private hExtHandle, hAppIdHandle As SafeRegistryHandle
' Windows API calls.
Private Declare Unicode Function RegOpenKeyEx Lib"advapi32.dll" _
Alias "RegOpenKeyExW" (hKey As IntPtr, lpSubKey As String, _
ulOptions As Integer, samDesired As Integer, _
ByRef phkResult As IntPtr) As Integer
Private Declare Unicode Function RegQueryValueEx Lib "advapi32.dll" _
Alias "RegQueryValueExW" (hKey As IntPtr, _
lpValueName As String, lpReserved As Integer, _
ByRef lpType As UInteger, lpData As String, _
ByRef lpcbData As UInteger) As Integer
Private Declare Function RegSetValueEx Lib "advapi32.dll" _
(hKey As IntPtr, _
<MarshalAs(UnmanagedType.LPStr)> lpValueName As String, _
reserved As Integer, dwType As UInteger, _
<MarshalAs(UnmanagedType.LPStr)> lpData As String, _
cpData As Integer) As Integer
Private Declare Function RegCloseKey Lib "advapi32.dll" _
(hKey As IntPtr) As Integer
' Windows API constants.
Private Const HKEY_CLASSES_ROOT As Integer = &h80000000
Private Const ERROR_SUCCESS As Integer = 0
Private Const KEY_QUERY_VALUE As Integer = 1
Private Const KEY_SET_VALUE As Integer = &h2
Private REG_SZ As UInteger = 1
Private Const MAX_PATH As Integer = 260
Public Sub New(fileExtension As String)
Dim retVal As Integer = 0
Dim lpType As UInteger = 0
If Not fileExtension.StartsWith(".") Then
fileExtension = "." + fileExtension
End If
ext = fileExtension
Dim hExtension As IntPtr = IntPtr.Zero
' Get the file extension value.
retVal = RegOpenKeyEx(New IntPtr(HKEY_CLASSES_ROOT), fileExtension, 0,
KEY_QUERY_VALUE, hExtension)
if retVal <> ERROR_SUCCESS Then
Throw New Win32Exception(retVal)
End If
' Instantiate the first SafeRegistryHandle.
hExtHandle = New SafeRegistryHandle(hExtension, True)
Dim appId As New String(" "c, MAX_PATH)
Dim appIdLength As UInteger = CUInt(appId.Length)
retVal = RegQueryValueEx(hExtHandle.DangerousGetHandle(), String.Empty, _
0, lpType, appId, appIdLength)
if retVal <> ERROR_SUCCESS Then
Throw New Win32Exception(retVal)
End If
' We no longer need the hExtension handle.
hExtHandle.Dispose()
' Determine the number of characters without the terminating null.
appId = appId.Substring(0, CInt(appIdLength) \ 2 - 1) + "\shell\open\Command"
' Open the application identifier key.
Dim exeName As New string(" "c, MAX_PATH)
Dim exeNameLength As UInteger = CUInt(exeName.Length)
Dim hAppId As IntPtr
retVal = RegOpenKeyEx(New IntPtr(HKEY_CLASSES_ROOT), appId, 0,
KEY_QUERY_VALUE Or KEY_SET_VALUE, hAppId)
If retVal <> ERROR_SUCCESS Then
Throw New Win32Exception(retVal)
End If
' Instantiate the second SafeRegistryHandle.
hAppIdHandle = New SafeRegistryHandle(hAppId, True)
' Get the executable name for this file type.
Dim exePath As New string(" "c, MAX_PATH)
Dim exePathLength As UInteger = CUInt(exePath.Length)
retVal = RegQueryValueEx(hAppIdHandle.DangerousGetHandle(), _
String.Empty, 0, lpType, exePath, exePathLength)
If retVal <> ERROR_SUCCESS Then
Throw New Win32Exception(retVal)
End If
' Determine the number of characters without the terminating null.
exePath = exePath.Substring(0, CInt(exePathLength) \ 2 - 1)
exePath = Environment.ExpandEnvironmentVariables(exePath)
Dim position As Integer = exePath.IndexOf("%"c)
If position >= 0 Then
args = exePath.Substring(position)
' Remove command line parameters ('%0', etc.).
exePath = exePath.Substring(0, position).Trim()
End If
openCmd = exePath
End Sub
Public ReadOnly Property Extension As String
Get
Return ext
End Get
End Property
Public Property Open As String
Get
Return openCmd
End Get
Set
If hAppIdHandle.IsInvalid Or hAppIdHandle.IsClosed Then
Throw New InvalidOperationException("Cannot write to registry key.")
End If
If Not File.Exists(value) Then
Dim message As String = String.Format("'{0}' does not exist", value)
Throw New FileNotFoundException(message)
End If
Dim cmd As String = value + " %1"
Dim retVal As Integer = RegSetValueEx(hAppIdHandle.DangerousGetHandle(), String.Empty, 0,
REG_SZ, value, value.Length + 1)
If retVal <> ERROR_SUCCESS Then
Throw New Win32Exception(retVal)
End If
End Set
End Property
Public Sub Dispose() _
Implements IDisposable.Dispose
Dispose(disposing:=True)
GC.SuppressFinalize(Me)
End Sub
Protected Sub Dispose(disposing As Boolean)
' Ordinarily, we release unmanaged resources here
' but all are wrapped by safe handles.
' Release disposable objects.
If disposing Then
If hExtHandle IsNot Nothing Then hExtHandle.Dispose()
If hAppIdHandle IsNot Nothing Then hAppIdHandle.Dispose()
End If
End Sub
End Class
