Clever Geek Handbook

How to call a method when binding a TextBox

I would like to bind () a textbox to an EditItemTemplate, but I need to pass the original value of the textbox to a function before displaying it. My goal is to format the value before displaying it. This is a complex formatting rule, so I cannot use any of the built-in formatters. It's easy to do when dealing with Eval (), but with Bind () it's a different story. I know it can be done using events in code, but I tried to do it all from the aspx page.

Example:

<EditItemTemplate>
        <asp:TextBox ID="NameTextBox" Text=<%# Bind("Name") %> MaxLength="255" runat="server" />
</EditItemTemplate>

Thank...

+3


source to share


2 answers


Something like this should be very close to what you are looking for:

<asp:TextBox Id="TextBox1" runat="server" Text='<%# FormatValue(Eval("Name"), Container.DisplayItemIndex) %>' />


And in the code:

public object FormatValue(object value, int itemIndex)
{
    var input = GridView1.Rows[itemIndex].FindControl("TextBox1") as TextBox;
    if (input != null)
    {
        //do whatever you need with the old value
        var oldValue = input.Text.Trim();
    }

    //format the value and send it back
    return string.Format("My name is {0}", value);
}
+3


source


You cannot do this from markup. ASP.NET has custom syntax code Bind

and generates custom code for it. Therefore, two way data binding does not support anything but Bind()

. You can find more information on this in How ASP.NET Data Binding Works with Eval () and Bind () Assertions of Eilon Lipton's article:

To the surprise of many readers, there is no binding method in ASP.NET! When ASP.NET parses your file and sees that you are using a data binding the expression (in the format angle-bracket-percentage-pound "<%# %>"

) has special code to parse the syntax Bind

and generate some special code for it. When you use <%# Bind("Name") %>

it is not a real function call. If ASP.NET parses the code and finds the Bind()

statement splits the statement into two parts. The first part is the one-way part of data binding, which ends with just a regular Eval()

call. The second part is the reverse part, which is usually some code along the lines "string name = TextBox1.Text"

that takes the value back from where it was associated.

The Non-Bind () binding operators are literal code (we use CodeSnippetExpressions

in CodeDom

), so arbitrary code in the language of your choice. However, because ASP.NET must parse Bind()

, two-way data binding does not support anything other than Bind()

. For example, the following syntax is invalid because it tries to call arbitrary code and be used Bind()

at the same time: <%# FormatNameHelper(Bind("Name")) %>

The only formats supported in two-way data binding are Bind("field")

and Bind("field", "format string {0}")

.



So, think about it in code, or use a method instead Eval

.

+4


source






More articles:


All Articles