如何使用C#从数据表中选择数据库的第一行数据？

Question

How can I select the first row of the data in the datatable? And display the content on a labelbox, and radiobuttons?

OleDbDataAdapter dAdap = new OleDbDataAdapter(command);
DataTable dTable = new DataTable();
dAdap.Fill(dTable);
foreach(DataRow row in dTable.Rows)
{
    question = row["QUESTION"].ToString();
    c1 = row["C1"].ToString();
    c2 = row["C2"].ToString();
    c3 = row["C3"].ToString();
    c4 = row["C4"].ToString();
    ans = row["ANSWER"].ToString(); 
}
lblQuest.Text = question;
btnA.Text = c1;
btnB.Text = c2;
btnC.Text = c3;
btnD.Text = c4;

I tried this code, but it only displays the last row. Also when I try to rerun the query. It didn't refresh/replace/overwrite the values, it only displays the last row of the first query.

edit:

i = 0;
x = 0;
lblQuest.Text = dTable.Rows[i].Field<string>(x);
btnA.Text = dTable.Rows[i].Field<string>(x + 1);
btnB.Text = dTable.Rows[i].Field<string>(x + 2);
btnC.Text = dTable.Rows[i].Field<string>(x + 3);
btnD.Text = dTable.Rows[i].Field<string>(x + 4);

Answer 1

是的，因为变量将在每次迭代时被覆盖，而您最终只会拥有最后一次迭代的值

Answer 2

If you want to select only first row values use dTable[0][ColumnIndex]

To load next row on button click do:

int currentRow = 0;
DataTable myDt;

private void LoadNextRow()
{
    currentRow++;
    myLabel.Text = myDt[currentRow]["MyColumn"].ToString();
}

private void OnButtonClick(....)
{
    LoadNextRow();
}

Answer 3

Your issue is that your variables are being overwritten with each loop. Once the loop gets through the whole DataTable it ends with the last row and only displays that.

To get the functionality you want you will need to store the DataTable as a property instead of a local variable.

One approach from there is to keep track of the row you are currently viewing. Then when the next button is clicked just ++ that current number and reassign the values.

class YourClass
{
    private DataTable dt { get; set; }
    private int CurrentRow { get; set; }

    private void SomeMethod()
    {
        OleDbDataAdapter dAdap = new OleDbDataAdapter(command);
        dt = new DataTable();
        dAdap.Fill(dt);
        CurrentRow = 0;
        AssignToRow();
    }

    private void AssignToRow()
    {
        var row = dt.Rows[CurrentRow];
        lblQuest.Text = row["QUESTION"].ToString();
        btnA.Text = row["C1"].ToString();
        btnB.Text = row["C2"].ToString();
        btnC.Text = row["C3"].ToString();
        btnD.Text = row["C4"].ToString();
    }

    private void NextButton_Click(object sender, EventArgs e)
    {
        CurrentRow++;
        AssignToRow();
    }
}