Develop Reference

NavigateUrl and Eval in a button

So I have this line of code which uses a hyperlink
<asp:HyperLink style="text-decoration:none" runat="server" Text="View Order" NavigateUrl='<%# "OrderDetails2.aspx?oID=" + Eval("oID") %>'>/asp:HyperLink>
Works perfectly fine but when I try to use a button to do the same thing (since I have to use an OnClick method), it doesn't allow me to use NavigateUrl and Eval in it. Any alternative methods?

Thats because asp:button does not have a property called NavigateUrl, its only a valid property for an hyperlink.
You can use JavaScript click event for an asp:hyperlink.

Not sure what you're trying to do.
If you are trying to add a link to another page, just use asp:hyperlink but use CSS to make it look like a button.
If you really do want a button with a server-side click event, you can add the following to the end of the click event handler:
Response.Redirect(String.Format("OrderDetails2.aspx?oID={0}", oID));

Retain html client control values on postback

How can I retain client side html controls on postback? I have tried setting enableviewstate="true" but that did not work. A workaround I've done was to build a server side function that takes all the posted values and resets them via ClientScript.RegisterStartupScript and call this on every postback method. Is there an easier and more time efficient way of doing this?

You have have html control to keep their values on postback by making them runat="server" e.g.
<input type="text" id="txt1" runat="server" />

You need to create the controls at every postback. If you're looking for something a little easier to implement, take a look at the DynamicControlsPlaceholder control. It's a nifty little control that takes away most of the pain associated with persisting dynamic content.

Can you use HiddenField?
Now on clicking any button at client side, Preserve the data in HiddenField.
Use JQuery document.ready function to set the value again from HiddenField again. JQuery docuemnt.ready will be called on each Postback.

Adding javascript functions to asp control

iv'e got an asp button which performs another task besides postback
i have done this by adding javascript code to the button as follows
if( !IsPostBack )
btn1.Attributes.Add("onclick", "f();");
i'm not sure of 2 things
the first :
where in the cs code i should add the function f() , currently i'm doing it in page load
while ignoring postbacks because then the function would have already been added(i might be wrong)
the second :
is there any to make the function execute only if the page was validated ? (after postback)
thanks in advance
eran.

I would use OnClientClick instead of adding the click event throug the attributes. As for your JavaScript, I would add it in the ASPX part. Depending on what the function does, you might be able to avoid the code behind all together and do something like this:
<asp:Button ID="Button1" runat="server" Text="Hi" OnClientClick="javascript:return f();" OnClick="Button1_Click" />
From your f() function, kick off the validation, and return true if validation passes, otherwise return false. If OnClientClick returns true the page will post back, and if it returns false the page will not post back.

1st Question
You will need to add it each time.
btn1.Attributes.Add("onclick", "f();");
2nd Question
You can check the validity of a page by checking the Page.IsValid Property

Unobtrusive JavaScript
If you're serious about javascript then you don't want to write inline javascript.
You will want to create an event handler in javascript code inside the script tags or in a external file.
If you're using .NET 4 server control id:s will be good, else I would use jquery's
contains selector. Search for the given server control ID.

page postback in asp.net?

in my application i have the playvideo page where video will play, below that i have the option for sharing the video like adding to favorite ,playlist and sending mail.
when i click on any of the link the page is postbacking and video will start from the first.
i place update panel for link button even though it is not working (video is playing from the first i.e., page is postbacking. can u help me. thank you

Actually, the part of page that is within the UpdatePanel does the postback. Make sure you have only those controls(for instance, your links) inside the UpdatePanel.
Alternatively, you can use multiple UpdatePanels; for instance one for your video and one for the links. In this case note that, when one UpdatePanel gets updated other UpdatePanels also gets updated, which you may not want; so all you have to do then is to mark the UpdateMode property to Conditional and call YourDesiredUpdatePanel.Update() method manually - whenever required.
Btw, updating selected portions of the page also reduces the load on the server
Or you may want to look into using client callbacks instead of a postback. But since client callback uses XMLHTTP, which means Microsoft implementation of AJAX, therefore callbacks are just awesome as long as your are working with IE.

You might want to try taking advantage of Page Methods to do the work you need done server side.
http://encosia.com/2008/05/29/using-jquery-to-directly-call-aspnet-ajax-page-methods/
Also, if you want to prevent a control from posting back, you can add return false to the end of your javascript onclick event on the control.
For example, if you had an asp button you were using you could do this:
<asp:Button ID="myButton" runat="server" OnClientClick="DoThingsInJavascript(); return false;" />
Or if you were just using a standard button you could say:
<input type="button" onclick="DoThingsInJavascript(); return false;" />

I've never really liked the update panel and I have sometimes found it's behaviour awful. Have you thought of trying something like a proper ajax call from Javascript

calling javascript function on selected index change of select input type in ASP.NET

Is there a way to call a javascript function when the selectedIndex of a select input has been changed?
Using this code in the c# code behind file
riskSeverityDropDown.SelectedValue = Convert.ToString(planRisk.Severity);
riskSeverityDropDown.SelectedIndexChanged += new EventHandler(riskSeverityDropDown_SelectedIndexChanged);
riskSeverityDropDown.AutoPostBack = true;
want to change something else on the page with javascript when the index is changed.
Any help would be much appreciated.
Thanks in advance

You're already going to server code (AutoPostBack is true), which means you're going to rebuild the entire page anyway. Running javascript at this point would be a little silly, because any changes you make to the DOM will be lost and any ajax requests you want to send can instead be handled by normal server code. If you really want to do this, you can just register the script to run when the page loads after the postback.
On the other hand, if you can do this without any server code at all then set AutoPostBack to false and the basic html select control has a nice onchange event you can handle.

Simply add an onchange to your asp:dropdownlist.
<asp:DropDownList ID="riskSeverityDropdown"
AutoPostBack="True"
SelectedIndexChanged="riskSeverityDropDown_SelectedIndexChanged"
onChange="functionName()"
runat="server" />
or to do this from codebehind use:
riskSeverityDropdown.Attributes["onchange"] = "functionName()";

You want to add an attribute to that drop down called "onchange" and set it to call a JavaScript method of your choosing.

Use JQuery. It exposes a rich set of events that you can use to code against practically anything in a uniform manner. It is also quite easy to learn, compact, and popular.
In short you can't go wrong if you use JQuery. It is meant to solve problems like this well.