C# 向现有数据表添加新行的问题

Question

我正在尝试在 onClick 时添加一个新行。但是，它取代了我现有的添加到新行的即时行。

代码如下：

Main.cs

protected void Button1_Click(object sender, EventArgs e)
{
    DateTime selectedDate = CalendarMain.SelectedDate;
    string SportType = ddlSportType.SelectedItem.ToString();
    string distance = ddlDistance.SelectedItem.ToString();

    plan wp = new plan();
    wp.Time_Start = selectedDate;
    wp.Duration = distance;
    wp.Activity = SportType;

    DataTable dt = wp.addPlanDetailDataRow();

    gvActivityList.DataSource = dt;
    gvActivityList.DataBind();
}

plan.cs

public DataTable addPlanDetailDataRow()
{
    DataTable dt = new DataTable();

    dt.Columns.Add("Activity");
    dt.Columns.Add("Duration");
    dt.Columns.Add("status");
    dt.Columns.Add("Time_Start");
    dt.Columns.Add("Plan_ID");

    DataRow newRow = dt.NewRow();

    dt.Rows.Add(newRow);

    return dt;
}

我不确定我错过了什么。请指导我了解我的错误。非常感谢

Answer 1

您的 DataTable 在 addPlanDetailDataRow 中本地定义。它应该在 class 范围和 instanstiated 中定义一次以保持以前的值。以某种方法在数据表中添加列，以便调用一次。

DataTable dt = new DataTable();
private InitDataTable() //This method should be called once
{
    dt.Columns.Add("Activity");
    dt.Columns.Add("Duration");
    dt.Columns.Add("status");
    dt.Columns.Add("Time_Start");
    dt.Columns.Add("Plan_ID");    
} 
public DataTable addPlanDetailDataRow()
{     
    DataRow newRow = dt.NewRow();    
    dt.Rows.Add(newRow);    
    return dt;
}

编辑

由于 DataTable 被声明为数据成员并且可供 class 的所有方法访问，因此您不需要 return 数据表。这将更改 addPlanDetailDataRow，如下所示。另请注意，您只是添加行而不是填充行。

public void addPlanDetailDataRow()
    DataRow newRow = dt.NewRow();
    newRow["Activity"] = "a1"; //These dummy values should be replaced by real values.
    newRow["Duration"] = "d1";
    newRow["status"] = "s1";
    newRow["Time_Start"] = "st1";
    newRow["Plan_ID"] = "p1";
    dt.Rows.Add(newRow);  
}

调用方法是

gvActivityList.DataSource = addPlanDetailDataRow();
gvActivityList.DataBind();

由于 DataBind 在 asp.net 中使用，您可能需要将 DataTable 放入 ViewState 或将数据放入 DataBase。

Answer 2

使用 ViewState 记住以前的值：

编辑 :-

  protected void Button1_Click(object sender, EventArgs e)
{
    DateTime selectedDate = CalendarMain.SelectedDate;
    string SportType = ddlSportType.SelectedItem.ToString();
    string distance = ddlDistance.SelectedItem.ToString();
    plan wp = new plan();
    wp.Time_Start = selectedDate;
    wp.Duration = distance;
    wp.Activity = SportType;

    DataTable dt = new DataTable();

    dt.Columns.Add("Activity");
    dt.Columns.Add("Duration");
    dt.Columns.Add("status");
    dt.Columns.Add("Time_Start");
    dt.Columns.Add("Plan_ID");


    DataTable dt1 = wp.addPlanDetailDataRow(dt);

    gvActivityList.DataSource = dt;
    gvActivityList.DataBind();
}
public DataTable addPlanDetailDataRow(DataTable dt)
{

     if (ViewState["Datatable"] != null)
    {
        dt = (DataTable)ViewState["Datatable"];
    }
    ViewState["Datatable"] = dt;
    DataRow dr = dt.NewRow();
    dr["Activity"]="value1";
    dr["Duration"]="value2";
    dr["status"]="value3";
    dr["Time_Start"]="value4";
    dr["Plan_ID"]="value5";

    dt.Rows.Add(dr);

    return dt;
}

Answer 3

我尝试了一个示例页面，它的工作原理见下面的代码。

//Persisting Data after PostBack 尝试将数据table放入Viewstate，查看

的大小

// Viewstate，通过启用 Tracing。如果不是太大且小于 1 MB，则使用 Viewstate，

// 因为它更高效并且不使用任何服务器资源。

Main.cs

 protected void btn1_Click(object sender, EventArgs e)
 {
    DateTime selectedDate = DateTime.Now;
    string SportType = "Dummy SportType";
    string distance = "Dymmy distance";
    plan wp = new plan();
    wp.Time_Start = selectedDate;
    wp.Duration = distance;
    wp.Activity = SportType;
    DataTable dt;
    if (ViewState["Datatable"] != null) // 
    {
        wp.dt = (DataTable)ViewState["Datatable"];
    }
    else
    {
        wp.InitDataTable();
    }        
    dt = wp.addPlanDetailDataRow();
    ViewState["Datatable"] = dt;
    gvActivityList.DataSource = dt;
    gvActivityList.DataBind();

}

plan.cs

public plan()
{
    //
    // TODO: Add constructor logic here
    //

}
public DataTable dt;
public void InitDataTable()
{
    dt = new DataTable();
    dt.Columns.Add("Activity");
    dt.Columns.Add("Duration");
    dt.Columns.Add("status");
    dt.Columns.Add("Time_Start");
    dt.Columns.Add("Plan_ID");
}
public DateTime Time_Start;
public string Duration;
public string Activity;

public DataTable addPlanDetailDataRow()
{
    DataRow newRow = dt.NewRow();
    newRow["Activity"] = this.Activity;
    newRow["Duration"] = this.Duration;
    newRow["status"] = "s1";
    newRow["Time_Start"] = this.Time_Start;
    newRow["Plan_ID"] = "p1";
    dt.Rows.Add(newRow);

    return dt;
}

C# 向现有数据表添加新行的问题

C# Issue with adding new row to existing datatable

.net

c#

asp.net