如何在實現者的方法之前執行基類的方法？

Question

我有以下頁面

public partial class GenericOfflineCommentary : OfflineFactsheetBase 
{ 
} 

其中OfflineFactsheetBase被定義爲

public class OfflineFactsheetBase : System.Web.UI.Page 
{ 
    public OfflineFactsheetBase() 
    { 
     this.Load += new EventHandler(this.Page_Load); 
     this.PreInit += new EventHandler(this.Page_PreInit); 
    } 

    protected void Page_PreInit(object sender, EventArgs e) 
    { 
     if (Request.QueryString["data"] != null) 
     { 
      this.PageData = StringCompressor.DecompressString(Request.QueryString["data"]); 
      this.ExtractPageData(); 
     } 
    } 
} 

OfflineFactsheetBase具有以下virtual方法：

public virtual void ExtractPageData() 
{ 
    // get stuff relevant to all pages that impmement OfflineFactsheetBase 
} 

這是在impmement OfflineFactsheetBase所有頁面實施如下：

public partial class GenericOfflineCommentary : OfflineFactsheetBase 
{ 
    public override void ExtractPageData() 
    { 
      // get stuff relevant to an OfflineCommentary page. 
    } 
} 

目前，只有GenericOfflineCommentary的ExtractPageData（）正在觸發。我怎樣才能修改這首先運行OfflineFactsheetBase的ExtractPageData（）然後GenericOfflineCommentary的？

編輯：我試圖避免必須在每個實現者中調用base.ExtractPageData()。這可能嗎？

Answer 1

充分利用ExtractPageData方法非虛，並調用ExtractPageDataInternal虛方法：

public void ExtractPageData() 
{ 
    // get stuff relevant to all pages that impmement OfflineFactsheetBase 

    // base implementation 
    ... 

    // call derived class implementation 
    this.ExtractPageDataInternal(); 
} 

protected virtual void ExtractPageDataInternal() 
{ 
    // implementation to be defined by derived class 
} 

的派生類只覆蓋ExtractPageDataInternal而不是ExtractPageData，所以基本實現將始終執行

Answer 2

澄清後的修訂

public class OfflineFactsheetBase : System.Web.UI.Page 
{ 
    public OfflineFactsheetBase () 
    { 
     this.Load += new EventHandler (this.Page_Load); 
     this.PreInit += new EventHandler (this.Page_PreInit); 
    } 

    protected void Page_PreInit (object sender, EventArgs e) 
    { 
     if (Request.QueryString [ "data" ] != null) 
     { 
      this.PageData = StringCompressor.DecompressString (Request.QueryString [ "data" ]); 
      this.ExtractPageData (); 
     } 
    } 

    public void ExtractPageData () 
    { 
     // get stuff relevant to all pages that implement OfflineFactsheetBase 
     // ....blah... 
     InternalExtractPageData (); 
    } 
    // Could be abstract if the class where 
    protected virtual void InternalExtractPageData () 
    { 
     // get stuff relevant to all pages that impmement OfflineFactsheetBase 
    } 
} 

public partial class GenericOfflineCommentary : OfflineFactsheetBase 
{ 
    public override void ExtractPageData () 
    { 
     // get stuff relevant to an OfflineCommentary page. 
    } 
} 

是OfflineFactsheetBase抽象？如果是這樣，請ExtractPageData保護抽象，從基礎上的公共方法調用它，見this SO question and answer