看不到下一个上一个或上一个和第一个记录 [英] can't see next previous or last and first records

问题描述

我在线尝试本教程，添加删除搜索和导航数据库。我已成功建立连接。我可以从Form_load调用NavitegateRecords但是btnNext或btnLast没有发生这种情况。我得到一个NullReferenceException bcoz dRow有空值。另外，只是为了检查是否传递了正确的值我使用了一个messageBox来检查objConnect.Sql的内容......但这是一个错误，说属性不能在这个上下文中使用，因为它缺少get访问器（所以我没有了解如何解决它暂时评论它）。我的代码如下：

I am trying this tutorial from online to add delete search and navigate a database. I have successfully made the connection. I could call the NavitegateRecords from Form_load But btnNext or btnLast such is not happening. Im getting a NullReferenceException bcoz the dRow has null value. Also just to check if correct value is passed I used a messageBox to check the content of objConnect.Sql...But this is giving an error saying "property cannot be used in this context because it lacks the get accessor"(So I not understanding how to solve it commented it out for the time being). My code is as follows:

    DatabaseConnection objConnect;
    string conString;

    DataSet ds;
    DataRow dRow;
        
    int MaxRows;
    int inc = 0;
    SqlConnection cnn = new SqlConnection();
    SqlDataAdapter daAdapter = new SqlDataAdapter();
        
    private void Form1_Load(object sender, EventArgs e)
    {
        DataSet ds=new DataSet();
        String SQ;
            
        objConnect = new DatabaseConnection();
        conString = Properties.Settings.Default.EmployeesConnectionString;
        //MessageBox.Show(conString);
        objConnect.connection_string = conString;
        SQ=Properties.Settings.Default.SQL;
        objConnect.Sql = SQ;
        MessageBox.Show(objConnect.Sql);
        ds = objConnect.GetConnection;
                
        MaxRows = ds.Tables[0].Rows.Count;
        MessageBox.Show(MaxRows.ToString());
        try
        {
            NavigateRecords(ds);
        }
        catch (Exception err)
        {
            MessageBox.Show(err.Message);
        }
    }
    private void NavigateRecords(DataSet ds)
    {
        dRow = ds.Tables[0].Rows[inc];
                       
        txtFirstName.Text = dRow.ItemArray.GetValue(1).ToString();
        txtSurname.Text = dRow.ItemArray.GetValue(2).ToString();
        txtJobTitle.Text = dRow.ItemArray.GetValue(3).ToString();
        txtDepartment.Text = dRow.ItemArray.GetValue(4).ToString();
    }

private void btnNext_Click(object sender, EventArgs e)
    {
        if (inc != (MaxRows-1))
        {
           inc= inc+1;
            NavigateRecords(ds);
        }
        else
        {
            if (inc != (MaxRows - 1))
            {
                inc = (MaxRows-1);
                NavigateRecords(ds);
            }
            MessageBox.Show("No More Rows");
        }
    }

    private void btnPrevious_Click(object sender, EventArgs e)
    {
        if (inc > 0)
        {
           inc= inc-1;
           NavigateRecords(ds);
        }
        else
        {
            if (inc != 0)
            {
                inc = 0;
                NavigateRecords(ds);
            }
            MessageBox.Show("First Record");
        }
    }

    private void btnLast_Click(object sender, EventArgs e)
    {
        if (inc != MaxRows - 1)
        {
            inc = MaxRows - 1;
            NavigateRecords(ds);
        }
    }

    private void btnFirst_Click(object sender, EventArgs e)
    {
        if (inc != 0)
        {
            inc = 0;
            NavigateRecords(ds);
        }
    }

推荐答案

从我提供的代码中我可以看到你没有在任何地方填充数据集。您确实设置了SQL语句和连接等，但我找不到对填写 [ ^ ]方法。如果这是真的，则没有从数据库中获取数据，从而使您的数据行不存在。

From the code you have provided as far as I can see you don't populate the dataset anywhere. You do set the SQL statement and the connection and so on but I can't find a call to Fill[^] method anywhere. If this is true there's no data fetched from the database thus leaving your data row non existent.

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