维护包含控件的面板列表。丢失事件处理程序

Question

我在页面顶部有两个按钮添加控件和清除控件。

单击添加控件触发一个函数，该函数创建一个新面板和一个新的DropDownList。

我为DropDownList指定了SelectedIndexChanged的Eventhandler。

这个想法是，根据我的DropDownList中的选择，我将在该面板中创建另一个控件。

最终面板将包含一些可以作为查询参数传递的字段。

我将面板存储在每次回发时重新创建的面板列表中。

我的问题是我可以添加面板，删除面板，并清除我的列表中的所有面板，但我似乎无法得到SelectedIndexChanged触发器触发......它似乎永远不会被分配或它在每个Postback中丢失。

我已经耗尽了我的谷歌搜索专业知识，我对自己感到非常沮丧。我接受建议/修复。

谢谢。

List<Panel> persistControls = new List<Panel>(); 

protected override void OnInit(EventArgs e) 
{ 
    if (Session["persistControls"] != null) 
    { 
     persistControls = (List<Panel>)Session["persistControls"]; 
     int count = 0; 

     foreach (Panel dynamicControl in persistControls) 
     { 
      AddQuestionTypeDropDownList(count); 
      dynamicControl.ID = "panel" + count; 

      Button btnRemove = new Button(); 
      btnRemove.Click += new EventHandler(btnDelete_Click); 
      btnRemove.Text = "Remove"; 
      btnRemove.CommandArgument = count.ToString(); 

      // Pushing to Placeholder 
      myPlaceholder.Controls.Add(dynamicControl); 
      myPlaceholder.Controls.Add(btnRemove); 
      count++; 
     } 
    } 
    base.OnInit(e); 
} 

// Calls three functions responsible for pulling from the Database and binding the Datagrid. 
protected void Page_Load(object sender, EventArgs e) 
{ 
    if (!IsPostBack) 
    { 
     GetClustersFromDatabase(userid); 
     BindGrid(); 
     BindState();    
    } 
} 

private DropDownList AddQuestionTypeDropDownList(int count) 
{ 
    DropDownList list = new DropDownList(); 

    list.ID = "list" + count;  
    list.Items.Add(new ListItem("--Select One--", "")); 
    list.Items.Add(new ListItem("Title", "1")); 
    list.Items.Add(new ListItem("Contact", "2")); 
    list.Items.Add(new ListItem("Date Created", "3")); 
    list.SelectedIndexChanged += new EventHandler(list_SelectedIndexChanged); 
    list.AutoPostBack = true; 

    return list; 
} 

private DropDownList AddQuestionTypeDropDownList() 
{ 
    DropDownList list = new DropDownList(); 
    list.Items.Add(new ListItem("--Select One--", "")); 
    list.Items.Add(new ListItem("Title", "1")); 
    list.Items.Add(new ListItem("Contact", "2")); 
    list.Items.Add(new ListItem("Date Created", "3")); 
    list.SelectedIndexChanged += new EventHandler(list_SelectedIndexChanged); 
    list.AutoPostBack = true; 

    return list; 
} 

protected void btnAdd_Click(object sender, EventArgs e) 
{ 
    try 
    { 
     Panel panelContainer = new Panel(); 
     panelContainer.ID = "panel" + persistControls.Count; 

     panelContainer.Controls.Add(AddQuestionTypeDropDownList()); 

     Button btnRemove = new Button(); 
     btnRemove.Click += new EventHandler(btnDelete_Click); 
     btnRemove.Text = "Remove"; 
     btnRemove.CommandArgument = persistControls.Count.ToString(); 

     myPlaceholder.Controls.Add(panelContainer); // Pushes the Panel to the page. 
     persistControls.Add(panelContainer);// Adds our Panel to the Control list 

     myPlaceholder.Controls.Add(btnRemove); // Pushes our Button to the page. 
     Session["persistControls"] = persistControls; // put it in the session 
    } 
    catch 
    { 
     throw; 
    } 
} 

private void list_SelectedIndexChanged(object sender, EventArgs e) 
{ 
    //I have no code here but thats because I currently can't even get it to fire. 
    try 
    { 

    } 
    catch 
    { 
     throw; 
    } 
} 

protected void btnClear_Click(object sender, EventArgs e) 
{ 
    try 
    { 
     Session["persistControls"] = null; 
     Response.Redirect(Request.Url.ToString()); 
    } 
    catch 
    { 
     throw; 
    } 
} 

protected void btnDelete_Click(object sender, EventArgs e) 
{ 
    try 
    { 
     int deleteThisOne = int.Parse(((Button)sender).CommandArgument); 
     persistControls.Remove(persistControls[deleteThisOne]); 
     Session["persistControls"] = persistControls;   
     Response.Redirect(Request.Url.ToString()); 
    } 
    catch 
    { 
     throw; 
    } 
}  

Answer 1

我能够通过我在foreach面板的列表迭代并具有嵌套的foreach在该面板上每个控制迭代来解决问题。我检查控件的类型并在每次回发中修复事件处理程序。