沒有被添加到泛型列表<string> Add方法

Question

代碼物業在JobQuote類：

public class JobQuote 
{ 
// Properties 
private List<string> _jobfilenames; 
public List<string> JobFileNames 
{ 
    get 
    { 
     if (_jobfilenames != null) 
      return _jobfilenames; 
     else 
     { 
      _jobfilenames = new List<string>(); 
      return _jobfilenames; 
     } 
    } 

    set { _jobfilenames = value; } 
} 

代碼物業在用戶控制

public JobQuote quote 
{ 
    get 
    { 
     if (ViewState["Quote"] != null) 
      return (JobQuote)ViewState["Quote"]; 
     else 
     { 
      JobQuote newQuote = new JobQuote(); 
      return newQuote; 
     } 
    } 
    set { ViewState["Quote"] = value; } 
} 

代碼在用戶控件的try塊，其中字符串不是被添加到字符串的通用列表中：

try 
     { 
      string filename = System.IO.Path.GetFileName(FileUploader.FileName); 
      quote.JobFileNames.Add(filename); 
     }  

我在做什麼wr翁？

Answer 1

您正在閱讀viewstate，但您從未分配。

public JobQuote quote 
{ 
    get 
    { 
     if (ViewState["Quote"] != null) 
      return (JobQuote)ViewState["Quote"]; 
     else 
     { 
      // you only construct a new instance but you dont assign it to the viewstate 
      JobQuote newQuote = new JobQuote(); 
      // add the following line to fix the problem 
      // ViewState["Quote"] = newQuote; 
      return newQuote; 
     }  
    } 

這意味着，下次你參考報價財產時，一個新的JobQuote實例將被創建，而不是返回

舊JobQuote實例

實現該清潔的方法是：

public JobQuote Quote 
{ 
    get 
    { 
     JobQuote result = ViewState["Quote"] as JobQuote; 
     if (result == null) 
     { 
      result = new JobQuote(); 
      ViewState["Quote"] = result; 
     } 

     return result; 
    } 
} 

Answer 2

您每次都要返回一個新的JobQuote實例。試試這個：

public JobQuote quote 
{ 
    get 
    { 
     if (ViewState["Quote"] != null) 
      return (JobQuote)ViewState["Quote"]; 
     else 
     { 
      JobQuote newQuote = new JobQuote(); 
      ViewState["Quote"] = newQuote; 
      return newQuote; 
     } 
    } 
    set { ViewState["Quote"] = value; } 
} 

或：

public JobQuote quote 
{ 
    get 
    { 
     if (ViewState["Quote"] == null) 
      ViewState["Quote"] = new JobQuote(); 

     return (JobQuote)ViewState["Quote"]; 
    } 
    set { ViewState["Quote"] = value; } 
}