往databale中添加多行的问题

Question

为什么单击Button2_Click按钮后出错，不能添加一新行public partial class _Default : System.Web.UI.Page
{    public DataSet DS=new DataSet();
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            DS.Tables.Add(CreateDataTable());
            GridView1.DataSource = DS;
            GridView1.DataBind();        }
    }
    private DataTable CreateDataTable()
    {
        DataTable dt = new DataTable();    
        dt.Columns.Add("ID", typeof(int));
        dt.Columns.Add("图像路径", typeof(string));
        dt.Columns.Add("链接网址", typeof(string));
        DataRow dr =dt.NewRow();
        dr["ID"] = "1";
        dr["图像路径"] = "image/11.jpg";
        dr["链接网址"] = "http://baidu.com";
        dt.Rows.Add(dr);
        dr = dt.NewRow();
        dr["ID"] = "2";
        dr["图像路径"] = "image/221.jpg";
        dr["链接网址"] = "http://sohu.com";
        dt.Rows.Add(dr);
        return dt;
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        DataRow dr = DS.Tables[0].NewRow();
        dr["ID"] = this.TextBox1.Text;
        dr["图像路径"] = this.TextBox2.Text;
        dr["链接网址"] = TextBox3.Text;
        DS.Tables[0].Rows.Add(dr);
        GridView1.DataSource = DS;
        GridView1.DataBind();
        
    }
}

Answer 1

因为你点击BUTTON ，导致页面POSTBACKpublic DataSet DS=new DataSet();
这行代码被执行

Answer 2

public partial class _Default : System.Web.UI.Page
{    public DataSet DS=ViewState["ds"]==null?new DataSet():(DataSet)ViewState["ds"];
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            DS.Tables.Add(CreateDataTable());
            GridView1.DataSource = DS;
            GridView1.DataBind();
            ViewState["ds"]=DS;
        }
    }
    private DataTable CreateDataTable()
    {
        DataTable dt = new DataTable();    
        dt.Columns.Add("ID", typeof(int));
        dt.Columns.Add("图像路径", typeof(string));
        dt.Columns.Add("链接网址", typeof(string));
        DataRow dr =dt.NewRow();
        dr["ID"] = "1";
        dr["图像路径"] = "image/11.jpg";
        dr["链接网址"] = "http://baidu.com";
        dt.Rows.Add(dr);
        dr = dt.NewRow();
        dr["ID"] = "2";
        dr["图像路径"] = "image/221.jpg";
        dr["链接网址"] = "http://sohu.com";
        dt.Rows.Add(dr);
        return dt;
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        DataRow dr = DS.Tables[0].NewRow();
        dr["ID"] = this.TextBox1.Text;
        dr["图像路径"] = this.TextBox2.Text;
        dr["链接网址"] = TextBox3.Text;
        DS.Tables[0].Rows.Add(dr);
        GridView1.DataSource = DS;
        GridView1.DataBind();
        ViewState["ds"]=DS;
    }
}