Is it possible to add drop down items throught javascript, and then get it on server side?
I have
<asp:DropDownList ID="testDropDown" CssClass="listClass" runat="server"/>
<asp:Button ID="saveButton" runat="server" Text="Добавить" OnClick="saveButtonClick" />
After page load javascript add items to drop down
$('.listClass').append("<option value='value1'>Text1</option>");
But after saveButton click i have empty drop down on server
Any dynamic changes that happen on the client-side will not be automatically replicated on the server side.
You need to record the fact the action took place somehow (using, for instance an <asp:HiddenField> control)... then on the post-back, check for whether the action happened and replicate the value that took place on the client.
Also, be careful, as ASP.NET will probably throw an exception due to the fact that control is returning a value that ASP.NET did not populate the control with in the first place. To counteract this, either set the EnableEventValidation="false" in your <#Page> declaration, or add all possible values using Page.ClientScript.RegisterForEventValidation
You cannot do this in ASP.NET because the values are contructed using the ViewState on the server side.
Check this. It may be helpful for you: Options added to <select> by javascript lost in postback
Related
Currently I have a site that loads everything on initial load (when it's not a postback). Then it proceeds to load more data that should be fine to load regardless if it's postback or not. I thought everytime the page is refreshed or the button is pressed there is a postback. What I thought that if the user doesn't go to another page, any action he takes will be a postback.
However I'm getting very inconsistent errors when the site is actually on a server and was curious if perhaps, when clicking a button after a bit of inactivity, will the server possibly forget about the previous activity and treat the action as the person hitting the site for the first time again?
Below is how the button is defined....
<asp:Button CssClass="btn btn-default controls" ID="btnAddAdditionalCom" runat="server" Text="Add Comment" OnClick="btnAddAdditionalCom_Click"/>
Any asp:button click will cause a postback to the server because asp is a server side language so it has to talk to the server to execute the button click. If you want to do button clicks without talking to the server use something like javascript
You cant modify it.
Because this is a essential concepts in asp.net.
Even you cant change the value of IsPostback Property (It has no setter).
If you want to treat Postback as page load then u forgot the need of IsPostback
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.
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.
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
How do I setup a default setting so that if I do not set an OnClick (i.e the asp.net OnClick attribute) explicitly for an asp:LinkButton tag, it will not render an onclick(html attribute for javascript) attribute client side? By default, asp.net adds an onclick='doPostBack....' for the LinkButton.
Case for use:
There is a LinkButton tag on the page. For this page, if the user has one friend, I only want to run client side code if the button is clicked and would not for any reason want to make a post back. If the user has more than one friend I would want a click to trigger a postback.
Solutions that include the following are not helpful:
Using any asp.net Ajaxtoolkit
Dynamically switching the control type (i.e. if friends == 1 use a asp:Hyperlink)
-I want to avoid this because it is not scalable. There might be many cases where I want an asp:Link tag to do a postback or to not do a postback depending on the user context or user attributes
Using OnClientClick (I am using jQuery would like to avoid this)
Solution that would be helpful if possible:
If I could see server side at runtime whether an OnClick event was explicitly set on an asp:LinkButton tag, this would solve my problem, too. any ideas?
How about rather than dynamically switching the controls (as you mentioned is a solution you don't want), you could always use an asp:HyperLink and set the NavigateUrl property to redirect your page back to itself with a query string of some sort indicating what was clicked.
If you don't want the post to happen at all, simply leave the NavigateUrl property blank.
Of course, this will be pretty worthless if the rest of the page is dependent on ViewState and such.
http://forums.asp.net/t/1129106.aspx
This link explains how to see server side at runtime whether an OnClick event was explicitly set using reflection