问题
I am facing troubles in creation of dynamic web controls. I have a SQL Databounded DropDownlist with DataTextField ="All_Columns" and DataValueField="DATA_TYPE".
Upon DropDownList1_SelectedIndexChanged i must check for the datatype as decimal or Varchar for the Selected value. If it is decimal i must call Createdynamicwebcontrols_decimal() and create DropDownList2. If it is varchar i must call Createdynamicwebcontrols_varchar().
Current Issue: Upon DropDownList2_SelectedIndexChanged i must create two dynamic textboxes and input values must be retained and search and display the data in a JQGrid with the help of Button Click event. But the DDL control hides completely
How to achieve above all features. Help needed please. New to dynamic web controls.
Aspx Code:
<asp:DropDownList ID="DropDownList5" runat="server" DataSourceID="column_list_for_filter" DataTextField="All_Columns" DataValueField="DATA_TYPE" OnSelectedIndexChanged ="DropDownList5_SelectedIndexChanged" AutoPostBack="true" >
</asp:DropDownList>
<asp:SqlDataSource ID="column_list_for_filter" runat="server" ConnectionString="<%$ ConnectionStrings:DatabaseConnectionString %>" SelectCommand="SELECT COLUMN_NAME AS 'All_Columns', DATA_TYPE FROM INFORMATION_SCHEMA.COLUMNS WHERE (TABLE_NAME = 'TABLE')"></asp:SqlDataSource>
C# code:
protected void Page_Load(object sender, EventArgs e)
{
Panel6.Visible = false;
JQGrid9.Visible = false;
if (Session["DataforSearch"] != null)
{
Panel6.Visible = true;
JQGrid9.Visible = true;
JQGrid9.DataSource = Session["DataforSearch"] as string;
}
}
protected void Page_PreInit(object sender, EventArgs e)
{
//How to Proceed
}
protected void DropDownList5_SelectedIndexChanged(object sender, EventArgs e)
{
if(DropDownList5.SelectedValue == "decimal")
{
createdynamiccontrols_decimal();
}
else if(DropDownList5.SelectedValue == "int")
{
createdynamiccontrols_int();
}
else if(DropDownList5.SelectedValue == "varchar")
{
createdynamiccontrols_varchar();
}
//How to Proceed
}
protected void createdynamiccontrols_decimal()
{
int i = DropDownList5.SelectedIndex;
++i;
TableRow row;
row = new TableRow();
TableCell cell1;
cell1 = new TableCell();
//DropDownList2
DropDownList Range_DDL;
Range_DDL = new DropDownList();
Range_DDL.ID = "RandeDDL" + i.ToString();
Range_DDL.Items.Insert(0, new ListItem("--Select--", "--Select--"));
Range_DDL.Items.Insert(1, new ListItem("Equal", "Equal"));
Range_DDL.Items.Insert(2, new ListItem("NotEqual", "NotEqual"));
Range_DDL.Items.Insert(3, new ListItem("greater than", "greater than"));
Range_DDL.Items.Insert(2, new ListItem("lesser than", "lesser than"));
Range_DDL.Items.Insert(2, new ListItem("greater than or equal to", "greater than or equal to"));
Range_DDL.Items.Insert(2, new ListItem("lesser than or equal to", "lesser than or equal to"));
Range_DDL.Items.Insert(2, new ListItem("Contains", "Contains"));
Range_DDL.Items.Insert(2, new ListItem("Is Null", "Is Null"));
Range_DDL.Items.Insert(2, new ListItem("Is Not Null", "Is Not Null"));
Range_DDL.Items.Insert(2, new ListItem("Between", "Between"));
Range_DDL.AutoPostBack = true;
Range_DDL.SelectedIndexChanged += new System.EventHandler(Range_DDL_SelectedIndexChanged);
cell1.Controls.Add(Range_DDL);
//// Add the TableCell to the TableRow
row.Cells.Add(cell1);
dynamic_filter_table.Rows.Add(row);
dynamic_filter_table.EnableViewState = true;
ViewState["dynamic_filter_table"] = true;
}
//DropdownList2 to create dynamic text boxes
protected void Range_DDL_SelectedIndexChanged(object sender, EventArgs e)
{
int j = DropDownList5.SelectedIndex;
++j;
TableRow row;
row = new TableRow();
TableRow rowtwo;
rowtwo = new TableRow();
TableCell cell1;
cell1 = new TableCell();
TableCell cell2;
cell2 = new TableCell();
TableCell cell3;
cell3 = new TableCell();
TextBox tb1;
tb1 = new TextBox();
TextBox tb2;
tb2 = new TextBox();
Label lbl1;
lbl1 = new Label();
Label lbl2;
lbl2 = new Label();
//// Set a unique ID for each TextBox added
tb1.ID = "lowerbound_" + j.ToString();
tb2.ID = "upperbound_" + j.ToString();
lbl1.Text = "LowerBound:";
lbl1.Font.Size = FontUnit.Point(10);
lbl1.Font.Bold = true;
lbl1.Font.Name = "Arial";
lbl2.Text = "UpperBound:";
lbl2.Font.Size = FontUnit.Point(10);
lbl2.Font.Bold = true;
lbl2.Font.Name = "Arial";
Button addmore;
addmore = new Button();
addmore.ID = "Button" + j.ToString();
addmore.Text = "+";
addmore.Click += new System.EventHandler(addmore_click);
cell1.Controls.Add(lbl1);
cell2.Controls.Add(tb1);
cell2.Controls.Add(lbl2);
cell2.Controls.Add(tb2);
cell3.Controls.Add(addmore);
row.Cells.Add(cell1);
row.Cells.Add(cell2);
rowtwo.Cells.Add(cell3);
dynamic_filter_table.Rows.Add(row);
dynamic_filter_table.EnableViewState = true;
ViewState["dynamic_filter_table"] = true;
}
//Button Click to retrieve the input from dynamic generated text box and display in JQGrid.
protected void Button1_Click(object sender, EventArgs e)
{
int j = DropDownList5.SelectedIndex;
++j;
Panel6.Visible = true;
JQGrid9.Visible = true;
TextBox lowerboundd = dynamic_filter_table.FindControl("lowerbound_" + j.ToString()) as TextBox;
TextBox upperbound = dynamic_filter_table.FindControl("upperbound_" + j.ToString()) as TextBox;
con.Open();
SqlDataAdapter da = new SqlDataAdapter("SELECT a,b,c FROM TABLE WHERE " + DropDownList5.SelectedValue + " >= " + lowerboundd.Text + " AND " + DropDownList5.SelectedValue + " <= " + upperbound.Text, con);
**//Problems in retrieving the input of textboxes - Object Reference error**
DataSet ds = new DataSet();
da.Fill(ds);
con.Close();
Session["DataforSearch"] = ds.Tables[0];
}
回答1:
You can find the source code and example on following link : http://www.codeproject.com/Articles/20714/Dynamic-ASP-NET-control-creation-using-C
I also found this code online, I hope it would help you: You can modify this according to your needs in this code Button is added on the click of an another button.
Adding a new control to a form is really easy.
All you have to do is create a new instance of the control like any other class. Eg:
Button NewButton = new button();
Then you fill out the properties of the control.
NewButton.Text = "My New Button";
After this setup an event handler.
NewButton.Click += new EventHandler(NewButton_Click);
Then in the button handler to tell which dynamic button was pressed you use the sender parameter.
void NewButton_Click(object sender, EventArgs e)
{
Button CurrentButton = (Button)sender;
CurrentButton.Text = "I was clicked";
}
Then finally the last step in setting the button up is to add the control to the form.
this.Controls.Add(NewButton);
来源：https://stackoverflow.com/questions/23469282/dynamically-generated-dropdownlist-web-controls-hides-on-selected