數據表編輯無法正確顯示

Question

我一直在尋找我的問題的答案很長一段時間了，我還沒有找到解決方案。 PS：我正在用德語進行測驗遊戲，所以你可能無法理解變量名等，但我認爲這不應該成爲問題。

我有在類SQL 8列一個DataTable，並在最後一列有一個0

namespace Quiz 
{ 
    class SQL 
    { 
     public static DataTable GEO_Fragen() 
     { 
      using (DataTable GEO = new DataTable("Geografie")) 
      { 

       GEO.Columns.Add("ID", typeof(int)); 
       GEO.Columns.Add("Frage", typeof(string)); 
       GEO.Columns.Add("Antwort 1", typeof(string)); 
       GEO.Columns.Add("Antwort 2", typeof(string)); 
       GEO.Columns.Add("Antwort 3", typeof(string)); 
       GEO.Columns.Add("Antwort 4", typeof(string)); 
       GEO.Columns.Add("Richtige Antwort", typeof(int)); 
       GEO.Columns.Add("Gefragt", typeof(int)); 

       GEO.Rows.Add(0, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(1, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(2, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(3, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(4, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(5, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(6, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(7, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(8, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(9, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(10, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(11, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(12, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(13, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(14, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(15, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(16, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(17, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(18, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 
       GEO.Rows.Add(19, "Question", "Answer 1", "Answer 2", "Answer 3", "Answer 4", 4, 0); 

       return GEO; 
      } 
     } 
     //...more code 

在另一類，我選擇一個隨機的問題。如果這個問題在最後一列中有一個「1」（意思是之前使用過），它會產生另一個。

public void Zufallszahl() 
{ 
    zufall = rnd.Next(0, SQL.GEO_Fragen().Rows.Count); 
    if (SQL.GEO_Fragen().Rows[zufall]["Gefragt"].ToString() == "1") 
    { 
     Zufallszahl(); 
    } 
    else 
    { 
     lbl_Frage.Text = SQL.GEO_Fragen().Rows[zufall]["Frage"].ToString(); //Filling in a random Question and Answers 
     rad_Antwort1.Text = SQL.GEO_Fragen().Rows[zufall]["Antwort 1"].ToString(); 
     rad_Antwort2.Text = SQL.GEO_Fragen().Rows[zufall]["Antwort 2"].ToString(); 
     rad_Antwort3.Text = SQL.GEO_Fragen().Rows[zufall]["Antwort 3"].ToString(); 
     rad_Antwort4.Text = SQL.GEO_Fragen().Rows[zufall]["Antwort 4"].ToString(); 

     rad_Antwort1.Checked = false; // No radio button is ticked 
     rad_Antwort2.Checked = false; 
     rad_Antwort3.Checked = false; 
     rad_Antwort4.Checked = false; 
    } 
} 

現在到了真正的問題：當我我選擇隨機行中改變最後一列的值，它是這樣做真的很快在調試模式。但之後，當我讓我顯示這個單元的值時，它再次顯示「0」。

private void btn_Weiter_Click(object sender, EventArgs e) 
{ 
    if (rad_Antwort1.Checked == true || rad_Antwort2.Checked == true || rad_Antwort3.Checked == true || rad_Antwort4.Checked == true) 
    { 
     Pruefen(); // Checking the chosen answer 
     lbl_Score.Text = "Punkte: " + Punkte; // Current points 
     string kontrolle = SQL.GEO_Fragen().Rows[zufall]["Antwort 1"].ToString(); 
     SQL.GEO_Fragen().Rows[zufall]["Gefragt"] = 1; //Changing value of the last column in row "zufall" to "1" 
     MessageBox.Show(SQL.GEO_Fragen().Rows[zufall]["Gefragt"].ToString()); //Shows "0" instead of "1" 

     if (rad_Antwort1.Text == kontrolle) // Next question 
     { 
      Zufallszahl(); 
      while (Counter <= 10) 
      { 
       Counter = Counter + 1; 
       break; 
      } 

      if (Counter > 10) 
      { 
       SQL.GEO_Fragen().Reset(); 
       btn_Weiter.Hide(); // After 10 questions back to main menu 
       lbl_Frage.Hide(); 
       rad_Antwort1.Hide(); 
       rad_Antwort2.Hide(); 
       rad_Antwort3.Hide(); 
       rad_Antwort4.Hide(); 
       lbl_Titel.Show(); 
       lbl_Themen.Show(); 
       rad_Geografie.Show(); 
       rad_Geschichte.Show(); 
       rad_Serien.Show(); 
       rad_Videospiele.Show(); 
       btn_Start.Show(); 
      } 
      //... more code 

我已經嘗試了很多不同的東西，我有AcceptChanges()，BeginEdit()和EndEdit()嘗試。僅僅爲了調試的目的，我也嘗試將DataTable和edit-command放到一個方法中。編輯然後完美地工作。

Answer 1

每次調用GEO_Fragen()方法時，都會創建一個DataTable的新實例。所以你正在更新一個實例並檢查一個完全不同的實例，這就是爲什麼它沒有更新。

您可以通過添加靜態字段和屬性您SQL類實現Singleton設計模式：

private static DataTable geoFragenInstance; 

public static DataTable GeoFragenInstance 
{ 
    get 
    { 
     if (geoFragenInstance == null) 
     { 
      geoFragenInstance = GEO_Fragen(); 
     } 

     return geoFragenInstance; 
    } 
} 

爲了確保只有永遠的SQL一個實例，你也應該添加一個私有的默認構造函數：

private SQL() {} 

否則，您將默認獲得一個公共的一個。

我也會讓你GEO_Fragen()方法private

然後用SQL.GeoFragenInstance

更換到SQL.GEO_Fragen()所有引用請注意，這是辛格爾頓和除其他事項外最簡單的實現不是線程安全的（其可能適合你的目的）。

延伸閱讀這裏：

Implementing Singleton in C#

Design Patterns - Singleton Pattern (4 Examples)