text changed event not fired

Question

I need to add 1 event for textbox into my webpage (created in ASP.NET with C#) and I was declared in the Page_Load function and into asp syntax:

 protected void Page_Load(object sender, EventArgs e)
    {
        textbox1.TextChanged += new EventHandler(textbox1_TextChanged);
    }

public void textbox1_TextChanged(object sender, EventArgs e)
{
    if (textbox1.Text == "ABCD")
    {
        Image1.Visible = true;
        textbox1.Enabled = false;
    }
}

and into asp page i used this statement:

<asp:TextBox Width="200" ID="textbox1" runat="server"></asp:TextBox>

I did debug and found that not execute textbox1_TextChanged function

Why ?

Answer 1

you need to set AutoPostBack to true .
see msdn for this:

To have the TextChanged event cause an immediate posting, set the TextBox control's AutoPostBack property to true.

Answer 2

Well, better late than never: you declared a method, strictly speaking, a handler for the event. But you didn't bind the event to the handler, like this:

<asp:TextBox Width="200" ID="textbox1" OnTextChanged="textbox1_TextChanged" runat="server"></asp:TextBox>

What you missed: OnTextChanged="textbox1_TextChanged"

In other words, your method would never be called because you never told the control that method was a handler for the event.

Answer 3

我认为值得一提的是，如果文本值实际未更改，则不会触发TextChanged事件，即您设置了文本，但将其设置为与以前相同的值。