无法从动态创建的文本框中获取值

Question

I have created a textbox programatically in page load as using the below code:

HtmlTableRow row = new HtmlTableRow();
HtmlTableCell cell1 = new HtmlTableCell();
HtmlTableCell cell2 = new HtmlTableCell();
cell1.Controls.Add(new Label() { ID = LableID1, Text = Name });
cell2.Controls.Add(new TextBox() { ID = TextBoxID1 });
row.Cells.Add(cell1);
row.Cells.Add(cell2);
dynamictable.Rows.Add(row);

And In the button click event i am trying to get the value from the Textbox and assign that value to anohter TextBox which is statically created as below:

string id = TextBoxID1                       
TextBox tb = (TextBox)dynamictable.FindControl(id);                        
string valuetext = tb.Text;
TextBox1.Text = valuetext;

Am getting Object Reference Error, I mean, i am not able to Find the control and create the TextBox.

I have tried to create the TextBox as below method also:

TextBox tb = (TextBox)form1.FindControl(id);                        
TextBox tb = (TextBox)this.form1.FindControl(id);                        
TextBox tb = (TextBox)page.FindControl(id);  

Any help would be highly helpful for me.

Answer 1

I think you might need to find the row and then the cell and then find the textbox.

Means inpite of doing this:

TextBox tb = (TextBox)dynamictable.FindControl(id);   

You need to find the specific row first like

// find by it or index etc
HtmlTableRow tb = (HtmlTableRow)dynamictable.FindControl(id);  

// Then find the Table cell and then find textbox..

I hope this will help you

Answer 2

You might have a method that creates the table, you need to call it on postback to ensure everything is setup.

protected HtmlTable dynamictable;
protected TextBox tb = new TextBox();


protected override void OnInit(EventArgs args)
{
 base.OnInit(args);
 CreateTableRows();
}

private void CreateTableRows()
{
 HtmlTableRow row = new HtmlTableRow();
 HtmlTableCell cell1 = new HtmlTableCell();
 HtmlTableCell cell2 = new HtmlTableCell();
 cell1.Controls.Add(new Label() { ID = LableID1, Text = Name });
 cell2.Controls.Add(tb });
 row.Cells.Add(cell1);
 row.Cells.Add(cell2);
 dynamictable.Rows.Add(row);
}

protected void OnClick(object sender, EventArgs args)
{
 return tb.Text;
}

Answer 3

In order to work with dynamic controls you need to fully understand the ASP.Net Page Life-cycle

Dynamic controls need to be recreated on each post , there's no magic behind responsible of creating your dynamic controls for you, sadly you have to create them explicitly.

Remember that a page is simply a class that is created when you perform a request and destroyed when the response is sent back to the user . Therefore controls need to be recreated every time. This is done for you when the controls are statically declared on the page. But with dynamic controls, you need to recreate them on each post

The code provided by @BobTodd is a good start point, however the recommendation from Microsoft is that dynamic controls should be created in the Page_Init event in order to sync their events with the rest of the static controls.

So your code would look like:

protected void Page_Init(object sender, EventArgs e)
{
 CreateTable();
}

Now, remember this simple rule of dumb, when working with dynamic controls, use always the same ID . This is really important because the page viewstate is loaded back based on the control's ID.

Another thing to consider is that all controls created in the Init event, won't load their viewstate until the LoadViewState method is called on every control on the page. This means that if you subscribe to the Page_PreLoad or Page_Load events, you can safely set the control's properties since their value were already loaded from the viewstate and therefore your new values won't be overridden.

This means that any property assigned to the controls before the PreLoad event, will be replaced by the page viewstate value . Therefore is considered a good practice to set your dynamic controls properties after the viewstate has been loaded.

As a quick view, check the ASP.Net page life-cycle:

Answer 4

use hidden field to store value of dynamically created text box in java script

also add runat="server" in hidden feild

and you can access your textbox value from hidden feild.

Another way is to store that value in query string using javascript and then reading from it at back end