有了以上的基礎(chǔ)后，我們看一段代碼，這段代碼是Dispose的一個(gè)實(shí)現(xiàn)，這個(gè)代碼如果仔細(xì)的去考慮的話，非常的有趣，在這里我們又會(huì)看到C#中一個(gè)非常常用的技術(shù)，多態(tài)性，如果你看過(guò)我在前面寫(xiě)的一篇關(guān)于虛擬方法的文章的話，你可以從中理解下面代碼的精要之處。

public class BaseResource: IDisposable
{
?// Pointer to an external unmanaged resource.
?// 非托管資源
?private IntPtr handle;
?// Other managed resource this class uses.
?// 托管資源
?private Component Components;
?// Track whether Dispose has been called.
?// 是否已經(jīng)釋放資源的標(biāo)志
?private bool disposed = false;

?// Constructor for the BaseResource object.
?public BaseResource()
?{
??// Insert appropriate constructor code here.
?}

?// Implement IDisposable.
?// Do not make this method virtual.
?// A derived class should not be able to override this method.
?// 提供給外部用戶顯示調(diào)用的方法，實(shí)際操作是在類的帶參數(shù)的虛函數(shù)Dispose(bool disposing)中實(shí)現(xiàn)
?public void Dispose()
?{
??// 表示用戶顯示調(diào)用
??Dispose(true);
??// Take yourself off the Finalization queue
??// to prevent finalization code for this object
??// from executing a second time.
??// 由于用戶是顯示調(diào)用，所以資源釋放不再由GC來(lái)完成
??GC.SuppressFinalize(this);
?}

?// 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 virtual void Dispose(bool disposing)
?{
??// Check to see if Dispose has already been called.
??// 如果已經(jīng)釋放，不做再次的操作，出現(xiàn)在用戶多次調(diào)用的情況下
??if(!this.disposed)
??{
???// If disposing equals true, dispose all managed
???// and unmanaged resources.
???if(disposing)
???{
????// Dispose managed resources.
????// 用戶是顯示調(diào)用的話，我們就要手工的操作托管資源
????Components.Dispose();
???}
???// Release unmanaged resources. If disposing is false,
???// only the following code is executed.
???CloseHandle(handle);
???handle = IntPtr.Zero;
???// Note that this is not thread safe.
???// Another thread could start disposing the object
???// after the managed resources are disposed,
???// but before the disposed flag is set to true.
???// If thread safety is necessary, it must be
???// implemented by the client.

??}
??disposed = true;????????
?}

?// Use C# destructor syntax for finalization code.
?// This destructor will run only if the Dispose method
?// does not get called.
?// It gives your base class the opportunity to finalize.
?// Do not provide destructors in types derived from this class.
?// 析構(gòu)函數(shù)
?~BaseResource()?????
?{
??// Do not re-create Dispose clean-up code here.
??// Calling Dispose(false) is optimal in terms of
??// readability and maintainability.
??// 表示本次調(diào)用是隱式調(diào)用，由Finalize方法調(diào)用，即托管資源釋放由GC來(lái)完成
??Dispose(false);
?}

?// Allow your Dispose method to be called multiple times,
?// but throw an exception if the object has been disposed.
?// Whenever you do something with this class,
?// check to see if it has been disposed.
?public void DoSomething()
?{
??if(this.disposed)
??{
???throw new ObjectDisposedException();
??}
?}
}

// Design pattern for a derived class.
// Note that this derived class inherently implements the
// IDisposable interface because it is implemented in the base class.
public class MyResourceWrapper: BaseResource
{
?// A managed resource that you add in this derived class.
?private ManagedResource addedManaged;
?// A native unmanaged resource that you add in this derived class.
?private NativeResource addedNative;
?private bool disposed = false;

?// Constructor for this object.
?public MyResourceWrapper()
?{
??// Insert appropriate constructor code here.
?}
??// 重寫(xiě)Dispose方法，釋放派生類自己的資源，并且調(diào)用基類的Dispose方法
?protected override void Dispose(bool disposing)
?{
??if(!this.disposed)
??{
???try
???{
????if(disposing)
????{
?????// Release the managed resources you added in
?????// this derived class here.
?????addedManaged.Dispose();????????
????}
????// Release the native unmanaged resources you added
????// in this derived class here.
????CloseHandle(addedNative);
????this.disposed = true;
???}
???finally
???{
????// Call Dispose on your base class.
????base.Dispose(disposing);
???}
??}
?}
}
// 在這里，派生類沒(méi)有實(shí)現(xiàn)~MyResourceWrapper和public Dispose方法，應(yīng)為他們已經(jīng)繼承了基類的這些特性，這也是我說(shuō)本示例代碼精要之處，他使用到了多態(tài)性原理，下面我會(huì)簡(jiǎn)單分析
// This derived class does not have a Finalize method
// or a Dispose method without parameters because it inherits
// them from the base class.

本示例中有兩個(gè)類一個(gè)是基類BaseResource,一個(gè)是派生類MyResourceWrapper,首先我們必須理解一下幾點(diǎn)：
1.類型的 Dispose 方法應(yīng)該釋放它擁有的所有資源。它還應(yīng)該通過(guò)調(diào)用其父類型的 Dispose 方法釋放其基類型擁有的所有資源。該父類型的Dispose 方法應(yīng)該釋放它擁有的所有資源并同樣也調(diào)用其父類型的 Dispose 方法，從而在整個(gè)基類型層次結(jié)構(gòu)中傳播該模式。
2.如果顯式的調(diào)用了Dispose方法，我們就在Dispose方法中實(shí)現(xiàn)托管資源和非托管資源的釋放，使用 GC.SuppressFinalize 方法來(lái)停止Finalize方法。因?yàn)槿绻脩粽{(diào)用了Dispose方法，那么我們就不必隱式的完成資源的釋放，應(yīng)為Finalizes會(huì)大大的減損性能。(Finalize一般只用于用戶沒(méi)有顯式的調(diào)用Dispose方法，需要我們隱式完成時(shí)才使用)
3.要確保始終正確地清理資源，Dispose 方法應(yīng)該可以被多次調(diào)用而不引發(fā)任何異常

好了，現(xiàn)在我們來(lái)看看這個(gè)程序的一個(gè)精要之處，那就是在派生類中，沒(méi)有公共的Dispose方法，和Finalize方法（就是析構(gòu)函數(shù)），那如果我們調(diào)用派生類對(duì)象時(shí)，是怎么實(shí)現(xiàn)資源釋放的呢，剛開(kāi)始我也不是很了解，后來(lái)仔細(xì)一看，突然發(fā)現(xiàn)其實(shí)很簡(jiǎn)單，它使用到了類的多態(tài)性來(lái)完成。
因?yàn)樵谂缮愔惺褂昧朔椒ㄖ貙?xiě)，所以在派生類中的Dispose(bool disposing)方法的派生度最大。由于基類中的Finalize和公共Dispose方法都是調(diào)用的是Dispose(bool disposing)方法，所以最終調(diào)用的是派生度最大的哪個(gè)函數(shù)，也就派生類中的Finalize和公共Dispose方法都是調(diào)用派生類自己的Dispose(bool disposing)方法。對(duì)于虛擬方法，可以參看我寫(xiě)的一篇文章地址是:

http://blog.csdn.net/juky_huang/archive/2005/10/26/517069.aspx

例如，現(xiàn)在我們有一個(gè)派生類實(shí)例A，如果我們顯示調(diào)用A.Dispose()方法，它會(huì)去調(diào)用基礎(chǔ)中的public Dispose方法這是由于繼承的原因，在public Dispose方法中調(diào)用的又是Dispose(bool disposing)方法，由于這個(gè)方法已經(jīng)被重寫(xiě)，所以它實(shí)際調(diào)用的不是基類中的Dispose(bool disposing)方法，而是A自己的Dispose(bool disposing)方法。這是根據(jù)運(yùn)行時(shí)類型來(lái)定的。所以最終還是實(shí)現(xiàn)了，先調(diào)用A中的資源釋放，然后才調(diào)用base.Dispose方法來(lái)完成基類的資源釋放。
如果用戶沒(méi)有顯示調(diào)用Dispose方法，那么Finalize方法就會(huì)有效，過(guò)程和上面是類似的。

從上面可以看出，對(duì)于非托管資源的釋放，有一個(gè)很好的規(guī)則，只要我們按照這個(gè)規(guī)則來(lái)做，你寫(xiě)的代碼就是.Net中的“良民”。

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