明確的價值

Question

我有這樣的代碼時，按下一個按鈕叫：

protected void Button1_Click(object sender, EventArgs e) 
{ 
    if (DropDownList1.SelectedItem.ToString() =="ER00 - File Header") 
    { 
     using (SqlConnection con = 
        new SqlConnection(ConfigurationSettings.AppSettings["DBcon"])) 
     { 
      if (String.IsNullOrEmpty(TextBox_ID.Text.ToString())) 
      { 
       lbl_NoBatchID.Text = "Please enter BatchID!"; 
      } 
      else 
      { 
       try 
       { 
        SqlCommand sqlCommand = new SqlCommand(
         "Select * from tbl_WinApps_FileHeader Where BatchID =" + 
         TextBox_ID.Text.ToString()); 

        sqlCommand.Connection = con; 
        con.Open(); 
        SqlDataReader read = sqlCommand.ExecuteReader(); 

        GridView1.DataSource = read; 
        GridView1.DataBind(); 
       } 
       catch (Exception) 
       {       
       } 
      } 
     } 
    } 
} 

這是它的工作原理：用戶輸入一個ID，然後按下按鈕時，它會顯示在表中SQL。

如果用戶沒有在文本框中輸入任何內容，它會提示「請輸入BatchID！」但在那之後，它會停留在那裏，即使我已經輸入了有效的ID，它也不會清除。任何想法，爲什麼？

Answer 1

ASP.NET頁面有一些名爲ViewState，可以維護請求之間的控件的狀態。您需要清除GridView的DataSource值並重新綁定它。

  if (String.IsNullOrEmpty(TextBox_ID.Text.ToString())) 
      { 
       lbl_NoBatchID.Text = "Please enter BatchID!"; 
       GridView1.DataSource=null; 
       GridView1.DataBind(); 
      } 
      else 
      { 

你也想清除錯誤如果查找成功：

catch(Exception e){ 
} 
lbl_NoBatchID.Text = ""; 

我也應該注意到，你的空catch()會吞噬你可能得到的任何數據庫或查找錯誤。

Answer 2

protected void Button1_Click(object sender, EventArgs e) 
{ 
    if (DropDownList1.SelectedItem.ToString() =="ER00 - File Header") 
    { 

     using (SqlConnection con = new SqlConnection(ConfigurationSettings.AppSettings["DBcon"])) 
     { 
      if (String.IsNullOrEmpty(TextBox_ID.Text.ToString())) 
      { 
       lbl_NoBatchID.Text = "Please enter BatchID!"; 

      } 
      else 
      { 
       try 
       { 

        SqlCommand sqlCommand = new SqlCommand("Select * from tbl_WinApps_FileHeader Where BatchID =" + TextBox_ID.Text.ToString()); 
        sqlCommand.Connection = con; 
        con.Open(); 
        SqlDataReader read = sqlCommand.ExecuteReader(); 

         GridView1.DataSource = read; 
         GridView1.DataBind(); 
        lbl_NoBatchID.Text = ""; 
       } 
       catch (Exception) 
       {       

       } 

      } 
     } 

    } 

Answer 3

在你的Else塊添加這行代碼。

lbl_NoBatchID.Text = "";