我們都知道，垃圾回收可以分為Dispose和Finalize兩類，關(guān)于這兩者的區(qū)別已經(jīng)太多了，一個是正常的垃圾回收GC所調(diào)用的方法，另外一個是終結(jié)器Finalizer，所調(diào)用的方法，在Effective C#一書中，有著明確的建議是說使用IDispose接口來代替Finalize。原因是因為Finalize終結(jié)會增加垃圾回收對象的代數(shù)，從而影響垃圾回收。

有了上述的原因，我們現(xiàn)在只來看使用IDispose接口的類。

在.NET中，絕大多數(shù)的類都是運行在托管的環(huán)境下，所以都由GC來負責(zé)回收，那么我們就不需要實現(xiàn)IDispose接口，而是由GC來自動負責(zé)。可是有一些類使用的是非托管資源，那么這個時候，我們就應(yīng)該去實現(xiàn)IDispose接口，說個比較常用的SqlConnection之類。

寫段常用的連接SQL語句的模型：

string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["Study1ConnectionString1"].ConnectionString; SqlConnection thisConnection = new SqlConnection(connectionString); thisConnection.Open(); SqlCommand thisCommand = new SqlCommand(); thisCommand.Connection = thisConnection; thisCommand.CommandText = "select * from [User]"; thisCommand.ExecuteNonQuery(); thisConnection.Close();

其實，作為非托管資源，為了防止我們忘記調(diào)用Close，一般都實現(xiàn)了Finalize，因此，即使我們沒有Close掉，也會由終結(jié)器將這塊內(nèi)存回收。但是，就增加了這塊垃圾的代數(shù)。

假設(shè)說我們寫了這樣的代碼：

string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["Study1ConnectionString1"].ConnectionString; SqlConnection thisConnection = new SqlConnection(connectionString); thisConnection.Open(); SqlCommand thisCommand = new SqlCommand(); thisCommand.Connection = thisConnection; thisCommand.CommandText = "select * form [User]"; //SQL語句錯誤 thisCommand.ExecuteNonQuery(); thisConnection.Close();

這樣的話，我們打開的SqlConnection就沒有關(guān)閉，只能等待Finalize去關(guān)閉了。

這是非常不好的做法。于是，我們可以想到異常處理：

SqlConnection thisConnection = null; try {string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["Study1ConnectionString1"].ConnectionString;thisConnection = new SqlConnection(connectionString);thisConnection.Open();SqlCommand thisCommand = new SqlCommand();thisCommand.Connection = thisConnection;thisCommand.CommandText = "select * form [User]";thisCommand.ExecuteNonQuery(); } finally {if (thisConnection != null){thisConnection.Close();} }

這樣做就不錯了，但是代碼看起來有些丑陋，可是使用using就讓代碼優(yōu)雅了很多，這也是C#比JAVA棒很多的地方，呵呵！

string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["Study1ConnectionString1"].ConnectionString; using (SqlConnection thisConnection = new SqlConnection()) {thisConnection.Open();SqlCommand thisCommand = new SqlCommand();thisCommand.Connection = thisConnection;thisCommand.CommandText = "select * form [User]";thisCommand.ExecuteNonQuery(); }

?

代碼量是不是小了很多呢？優(yōu)雅了許多呢！

其實，在IL的位置，代碼仍然是一樣的，他同樣把代碼給編譯成了try-finally的處理形式！

接下來，再來看下我們常用的使用數(shù)據(jù)庫的方式：

string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["Study1ConnectionString1"].ConnectionString; SqlConnection thisConnection = new SqlConnection(connectionString); thisConnection.Open(); SqlCommand thisCommand = new SqlCommand(); thisCommand.Connection = thisConnection; thisCommand.CommandText = "select * from [User]"; SqlDataReader thisReader = thisCommand.ExecuteReader(); thisReader.Close(); thisConnection.Close();

?

還是上面的問題，我們考慮用using語句來將之代碼重構(gòu)：

string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["Study1ConnectionString1"].ConnectionString; using (SqlConnection thisConnection = new SqlConnection(connectionString)) {thisConnection.Open();SqlCommand thisCommand = new SqlCommand();thisCommand.Connection = thisConnection;thisCommand.CommandText = "select * from [User]";using (SqlDataReader reader = thisCommand.ExecuteReader()){while (reader.Read()){ //操作}} }

我先把這段代碼翻譯成我們熟悉的try-finally的處理形式：

SqlConnection thisConnection = null; try {string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["Study1ConnectionString1"].ConnectionString;thisConnection = new SqlConnection(connectionString);thisConnection.Open();SqlCommand thisCommand = new SqlCommand();thisCommand.Connection = thisConnection;thisCommand.CommandText = "select * from [User]";SqlDataReader reader = null;try{reader = thisCommand.ExecuteReader();while (reader.Read()){//操作}}finally{reader.Close();} } finally {thisConnection.Close(); }

更丑陋的代碼吧！所以有個原則是：盡量避免using語句的嵌套。

怎么樣解決呢？很容易，自己寫我們的try-finally吧！

SqlConnection thisConnection = null; SqlDataReader reader = null; try {string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["Study1ConnectionString1"].ConnectionString;thisConnection = new SqlConnection(connectionString);thisConnection.Open();SqlCommand thisCommand = new SqlCommand();thisCommand.Connection = thisConnection;thisCommand.CommandText = "select * from [User]";reader = thisCommand.ExecuteReader();while (reader.Read()){//操作} } finally {if (thisConnection != null){thisConnection.Close();}if (reader != null){reader.Close();}}

這樣就好了！

關(guān)于using 的這節(jié)我就寫到這，最后對全文做個總結(jié)，其實就是一句話：盡量使用using來進行非托管資源的資源回收。

總結(jié)

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