一个放在用户控件中的HtmlInputFile在用户控件中代码,操作其,出错,未将对象引用设置到实例,在线等

Question

make sure the ascx's parent page has 
<form enctype="multipart/form-data" runat="server">

Answer 1

public string Text
            {
                  get
                  {
                    EnsureChildControls();
                        return label.Text;
                  }
                  set
                  {
                    EnsureChildControls();
                        label.Text = value;
                  }
            }protected override void CreateChildControls() 
            {
                  
                  Controls.Add(new LiteralControl("<h3>Enter a number : "));
                  
                  TextBox box1 = new TextBox();
                  box1.Text = "0";
                  Controls.Add(box1);
                  
                  Controls.Add(new LiteralControl("</h3>"));
                  
                  Controls.Add(new LiteralControl("<h3>Enter another number : "));
                  
                  TextBox box2 = new TextBox();
                  box2.Text = "0";
                  Controls.Add(box2);
                  
                  Controls.Add(new LiteralControl("</h3>"));
                  
                  Button button1 = new Button();
｝在引用之前调用EnsureChildControls();在CreateChildControls() 初始化子控件，这样，如果调用EnsureChildControls()时没有子控件，则系统调用CreateChildControls() 来创建子控件

Answer 2

<form enctype="multipart/form-data" runat="server">