Causing auto post back by typing text into TextBox without pressing enter or tab

问题

I want my asp.net TextBox to cause auto postback and activate a sever side event upon typing text into the TextBox without pressing enter or tab, similar to WinForms. Is this possible? If so is it possible to have this happen only after typing a certain number of characters such as three or four? Thank you.

回答1:

You cannot compare Windows-Applications and WebApplications. To post back to server when the user enters a char means that all HTML must be recreated from ASP.NET and send back to the client. But here is an example:

aspx:

<script type="text/javascript">
   var MIN_TEXTLENGTH = 3;

   function checkPostback(ctrl) {
     if (ctrl != null && ctrl.value && ctrl.value.length >= MIN_TEXTLENGTH) {
         __doPostBack(ctrl.id, '');
     }
   }
</script>


<asp:TextBox ID="TextBox1" OnKeyUp="checkPostback(this);" AutoPostBack="true" OnTextChanged="TextChanged" runat="server"></asp:TextBox>

Codebehind:

Protected Sub TextChanged(ByVal sender As Object, ByVal e As EventArgs)
    TextBox1.Attributes.Add("onfocus", "javascript:this.value=this.value;")
    TextBox1.Focus()
End Sub

回答2:

TextChange event of TextBox would become blur event in JavaScript. This means that it can fire a post back, only when you leave the control (TextBox which in client-side is an input or textarea) and the value is changed. So, that's not possible without tricks.

However, about your architecture (the way you want to post back the information to the server), I gotta say that it won't work buddy. Post backs are really expensive and you should avoid them as much as possible. My suggestion is to use ajax combined with keydown event of the input box.

回答3:

You could do this using Ajax & the onkeypress event plus some sort of counter.

So you wire a function to the onKeyPress event of your textarea, which increments a counter each time it fires, when this number gets to 3 or 4, you cal an ajax function which posts the form to the server in the background and then reset the counter again.

This will cause the form to be posted in the background for every 3rd or 4th keypress that happens while the textarea is in use, which is every keypress - space, enter, backspace etc...