好像我的编码错了。帮助任何人 [英] It seem like my coding is wrong. Help anybody

问题描述

第32行：{

第33行：}

第34行：SqlDataAdapter da = new SqlDataAdapter（select * from tblStudent，con）;

第35行：DataSet ds = new DataSet（）;

第36行：da.Fill（ds）;



< b>我尝试了什么：



private void BindGridViewData（）

{

string CS = ConfigurationManager.ConnectionStrings [DBCS]。ConnectionString;

using（SqlConnection con = new SqlConnection（CS））

{

}



SqlDataAdapter da = new SqlDataAdapter（select * from tblStudent，con）;

DataSet ds = new DataSet（）;

da.Fill（ds）;

gvStudent.DataSource = ds;

gvStudent.DataBind（）;

解决方案

我想在提供的解决方案中添加几点：



（1）数据Set 由 DataTable 组成，因为你只从SQL中选择了一个表 SELECT 查询，然后使用 DataTable 而不是 DataSet 更有意义。



（2）习惯于放置食用资源的对象，例如 SqlConnection ， SqlCommand 和 SqlDataAdapter 以确保对象在使用后正确处理。



您的代码现在看起来像这样：

  string  dbConnectionString = ConfigurationManager.ConnectionStrings [  DBCS]。ConnectionString; 
  string  sqlStatement =   SELECT * FROM tblStudent ; 
 使用（SqlConnection connection =  new  SqlConnection（dbConnectionString））{
 使用（SqlCommand cmd =  new  SqlCommand（sqlStatement，connection））{
  using （SqlDataAdapter da =  new  SqlDataAdapter（cmd））{
 DataTable dt =  new  DataTable（）; 
 da.Fill（dt）; 
  if （dt.Rows.Count >   0 ）{
 gvStudent.DataSource = dt; 
 gvStudent.DataBind（）; 
} 
 其他 {
  //  未找到结果 
} 
} 
} 
} 

快速提示：如果您在Page_Load事件中绑定 GridView ，请确保在中包装代码以进行绑定！IsPostback 阻止：

 受保护  void  Page_Load（ object  sender，EventArgs e）{
  if （！IsPostBack）{
  //  您的GridView绑定代码 
} 
} 




编译并不意味着您的代码是正确的！ ：笑：

将开发过程想象成编写电子邮件：成功编译意味着您使用正确的语言编写电子邮件 - 例如英语而不是德语 - 而不是电子邮件包含您的邮件想发送。



所以现在你进入第二阶段的发展（实际上它是第四或第五阶段，但你将在之后的阶段进入）：测试和调试。



首先查看它的作用，以及它与你想要的有何不同。这很重要，因为它可以为您提供有关其原因的信息。例如，如果程序旨在让用户输入一个数字并将其翻倍并打印答案，那么如果输入/输出是这样的：

输入预期输出实际输出
 1 2 1 
 2 4 4 
 3 6 9 
 4 8 16 

然后很明显问题出在将它加倍的位 - 它不会将自身加到自身上，或者将它乘以2，它会将它自身相乘并返回输入的平方。

所以，你可以查看代码和很明显，它在某处：

  private   int   Double （ int   value ） 
 {
  return   value  *  value ; 
} 

一旦你知道可能出现的问题，就开始使用调试器找出原因。在方法的第一行放置一个断点，然后运行你的应用程序。当它到达断点时，调试器将停止，并将控制权移交给您。您现在可以逐行运行代码（称为单步执行）并根据需要查看（甚至更改）变量内容（哎呀，您甚至可以更改代码并在需要时再试一次）。 />
在执行代码之前，请考虑代码中的每一行应该做什么，并将其与使用Step over按钮依次执行每一行时实际执行的操作进行比较。它符合您的期望吗？如果是这样，请转到下一行。

如果没有，为什么不呢？它有什么不同？

希望这可以帮助你找到代码的哪个部分有问题，以及问题是什么。

这是一项技能，它是一个值得开发的，因为它可以帮助你在现实世界和发展中。和所有技能一样，它只能通过使用来改进！




是的，你的代码错了。



尝试移动你的数据库操作进入使用块。

您还需要在尝试填充数据集之前打开连接

< pre lang =c＃> 使用（SqlConnection con = new SqlConnection（CS））
{ // SQL命令属于此处。不要忘记打开/关闭连接
}

SqlDataAdapter da = new SqlDataAdapter（ 选择*来自tblStudent，con）;




Line 32: {
Line 33: }
Line 34: SqlDataAdapter da = new SqlDataAdapter("Select * from tblStudent", con);
Line 35: DataSet ds = new DataSet();
Line 36: da.Fill(ds);

What I have tried:

private void BindGridViewData()
{
string CS = ConfigurationManager.ConnectionStrings["DBCS"].ConnectionString;
using (SqlConnection con = new SqlConnection(CS))
{
}

SqlDataAdapter da = new SqlDataAdapter("Select * from tblStudent", con);
DataSet ds = new DataSet();
da.Fill(ds);
gvStudent.DataSource = ds;
gvStudent.DataBind();

解决方案

I'd like to add a couple of points to the solutions provided:

(1) DataSet is composed of DataTables, and since you were only selecting one Table from your SQL SELECT query, then it makes more sense to use DataTable instead of DataSet.

(2) Make it a habit to put objects that eat resources such as SqlConnection, SqlCommand and SqlDataAdapter within a using block to ensure that objects will be properly disposed and after they are used.

Your code would now look something like this:

string dbConnectionString = ConfigurationManager.ConnectionStrings["DBCS"].ConnectionString;
string sqlStatement = "SELECT * FROM tblStudent";
using(SqlConnection connection = new SqlConnection(dbConnectionString)){
      using(SqlCommand cmd = new SqlCommand(sqlStatement ,connection)){
			using(SqlDataAdapter da = new SqlDataAdapter(cmd)){
				DataTable dt = new DataTable();
				da.Fill(dt);
				if(dt.Rows.Count > 0){
					gvStudent.DataSource = dt;
					gvStudent.DataBind();
				}
				else{
					//no result found		
				}		
			}
      }
}

Quick tip: If you are binding your GridView in your Page_Load event, then make sure to wrap your code for binding within !IsPostback block:

protected void Page_Load(object sender, EventArgs e){
        if (!IsPostBack){
            // Your code for binding your GridView here
        }
}




Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

private int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!




Yep, your code is wrong.

Try moving your database operations into the using block.
You will also need to open the connection before you try to fill the dataset

using (SqlConnection con = new SqlConnection(CS))
{ // SQL commands belong here. Don't forget to open/close the connection
}

SqlDataAdapter da = new SqlDataAdapter("Select * from tblStudent", con);




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