What do (TextBox) and Controls[0] mean in this code?

Question

Hi, now at school we are learning how to use GridView. We have a table with all the information of all the users. When we want to update a row, we need to store name, last name and other data in separate variables. Our teacher does it this way:

GridViewRow changedRow = GridView1.Rows[e.RowIndex];
string firstName = ((TextBox)changedRow.Cells[1].Controls[0]).Text;

I don't understand what are (TextBox) and Controls[0]? What do they do? What are they used for?

Answer 1

(TextBox)

That's a "type boxing", means forcing to convert to a specific data type, see Boxing and Unboxing (C# Programming Guide)

Controls[0]

That's simply accessing the first (zero-based) element of an array, see Array Class

Answer 2

(TextBox) is a cast (not an box/unbox).

https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/types/casting-and-type-conversions

as you might guess Cells is an army of cells of a grid row. .Controls is a collection of Controls in the cell. the author assumes the first control in the second cell is a TextBox (which inherits from Control). The cast allows accessing unique TextBox properties like .Text. if the control is not a TextBox, the cast will throw a runtime error.

box/unbox is for converting value types to objects and back. most commonly used for numeric types. this is a feature f most typed languages. you either pass the actual value via the stack, or you pass a value pointer allocated on the heap.

Answer 3

Hi @MikeR

First of all

GridViewRow changedRow = GridView1.Rows[e.RowIndex];

Declare a variable of type GridViewRow whose value is the "e.RowIndex+1" row of GridView1.

string firstName = ((TextBox)changedRow.Cells[1].Controls[0]).Text;

Declare a string variable firstname. Strongly convert this GridViewRow variable to a TextBox variable via '(TextBox)changedRow'. (Provided you can convert this control to a TextBox control.)

‘Cells[1]. Controls[0]' represents the first Control of the second Row.

ForExample

Code:

<asp:GridView ID="GridView1" runat="server" DataSourceID="SqlDataSource1" AutoGenerateColumns="false">
            <Columns>
                <asp:TemplateField HeaderText="D1">
                    <ItemTemplate>
                        <asp:TextBox ID="D1" runat="server" Text='Test1'></asp:TextBox>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText="D2">
                    <ItemTemplate>
                        <asp:TextBox ID="D2" runat="server" Text='Test2'></asp:TextBox>
                    </ItemTemplate>
                </asp:TemplateField>
            </Columns>
</asp:GridView>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>

 GridViewRow a = GridView1.Rows[0];
            string firstname = ((TextBox)a.Cells[0].Controls[1]).Text;
            TextBox1.Text = firstname;

Result:

Best regards,
Qi You

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