What's a simple good way to find out if a html button (the newer not input) caused the postback?
If the button is a HtmlButton control then you can just handle its ServerClick event:
<button id="MyButton" runat="server" onserverclick="MyButton_Click">Foo</button>
And then in your code-behind:
protected void MyButton_Click(object sender, EventArgs e)
{
// if you reach here it means that MyButton was clicked
}
Easiest way to do it is to add an OnClick event and just add sample code in the code behind. Then I usually add a breakpoint in the code.
I'm assuming you want to know how server-side ASP.NET code can determine if a given HTML button was pressed to cause the post back?
I can't think of any excellent solutions. Two sub-par solutions below:
1.) Add a client-side onclick to the button and have it modify a form element that the server has access to (i.e. hdnButtonClicked). The page_load will check that element and the value will allow it to determine if the HTML button was clicked.
2.) Have the button trigger a server-side method. Easiest way is to convert the button to an ASP.NET control and wire it up with an event handler but I'm sure you could work up some JavaScript to trigger a server-side method.
Unfortunately, I don't think information pertaining to how an HTML form was submitted is available on post back without some form of client side preparation. ASP.NET does this behind the scenes.
Related
There is an event onSelectedIndexChange for DropDownList in ASP.NET which triggers when a selected index is changed for a dropdown.
I have encountered a situation where I need to trigger similar kind of event when SelectedIndex of DropDown does not change upon selection.
I am totally puzzled what to do in such a case?
Any help/references will highly be appreciated.
Thank you.
I think that is normal. The event is SelectedIndexChanged and you said you selected the same item that was previously selected before. So the index remains the same, not changed, and the event won't fire. May be you look at OnClick.
The issue is that you have not changed the index when you clicked the second time, so the dropdown is still waiting for you to change it
Assuming you have another server-side control on your page that causes a postback, you could write a routine in the postback event for the other control that compares the current selection with the previous selection and fire a custom-event (or the routines you want to happen) if the value has not changed.
That said, I have to imagine there's an easier way to accomplish the overall goal you're trying to achieve, but you'll have to be a little more specific in your question.
UPDATE
I have to assume that you are using the value from the dropdown when you are processing the form. Why not start off with the dropdown hidden and the linkbutton shown? Just select a default from the dropdown list and allow the user to change it as needed.
Here's a fiddle showing that behavior: http://jsfiddle.net/rjaum/
That's fairly easy.
You can achieve this using javascript/jquery/server side code etc. Assuming user does click the control.
Something like this on pageLoad
PageLoad()
{
YourDropDownList.Attributes.Add("onclick","javascript:CallHelloWorld();return false;");
}
Then on server side you can decorate a method with WebMethod attribute
[WebMethod()]
public static string HelloWorld()
{
return "Hello foo";
}
On your client side aspx you can use jQuery to call your webmethod
<script language="text/javascript">
function CallHelloWorld()
{
// Call HelloWorld webmethod using jQuery $.ajax
}
</script>
Edit
You can use a radiobutton list instead of dropdownlist. That way, on client side you can check the event when the radio button is clicked that it is checked or not (if its checked fire your event).
Edit
Also try looking at this thread if you want to use dropdown list specificallyFire event each time dropdown list is selected with JQuery
assign an a event handler to the selected index changed event and set autopostback to true
in markup
or code behind
mydropdownlist.SelctedIndexChanged += NameOfMethod
the handler is then defined like this
protected void NameOfMethod(object sender, EventArgs e)
{
//your code here
}
update
by definition the selectedindexchanged event would only fire when the index changes. if you want to force the postback that will require some javascript. here is an example of how to do that with jquery
$(function() {
$('select').change();
});
I would like to disable postback on a onClick event of a button.
I did some research online and most are using onClientClick and using javascript. Is there a way to call a asp.net function "btnCommit_Click" on the onClick instead of using onclientclick and using javascript?
If not, how would I be able to incorporate a asp.net function with javascript?
<asp:Button ID="btnCommit" runat="server" Text="Save" TabIndex="5"
onclick="btnCommit_Click" />
UPDATED
I have a GridView which contains checkboxes, once the user makes their changes and click on a "Save Button" a Post Back occurs and I loose all the selections made to the checkboxes I was thinking of disabling the postback on the OnClick Event of the button would solve that issue...
I didn't exactly get what you are trying to achieve. But if you want to have both js and server-side to gether on an asp.net button, use OnClientClick and Onclick together. if you want to cancel the postback, return false in the OnClientClick js function. This way, the server-side OnClick event will never be called. otherwise, return true and the postback will occur.
Update:
Based on the comments and you update, if you want to persist the state of checkboxes in your gridview, you have to avoid overwriting anything that can affect you controls' states in the Page_Load event. What this simply means that you have to check for (IsPostback) in Page_Load event, and if it's true, you shouldn't do anything on your UI elements or you will lose their states.
Sounds like your problem is not putting your databinding and page setup inside a check for first page load.
http://msdn.microsoft.com/en-us/library/system.web.ui.page.ispostback.aspx
private void Page_Load()
{
if (!IsPostBack)
{
// Do your databinding etc here to stop it occuring during postback
}
}
I have a GridView which contains checkboxes, once the user makes their
changes and click on a "Save Button" a Post Back occurs and I loose
all the selections made to the checkboxes
You have to keep the Page_Load under Page.IsPostback during is's value to false like below..
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
//Your code
}
}
This will not cause to loose you grid checkbox selection made after clicking the button.
Your GridView EnableViewState must be True
Your template fields must be in designer page
While you can use VBScript with Internet Explorer only (I don't believe any other browsers support it), it is considered bad practice. To run VB/C#.net, you have to do some sort of postback/callback to the server. Other than that, use Javascript.
Dont use Autopostback=true to any form controls,if you want to send the form data to the server side function
*Form Page*
asp:Button ID="btn" runat="server" Text="Post Scrap" OnClick="btn_Click"
*Server side*
Sub btn_Click()
//code here
End Sub
In most of my cases, what I do is convert the button to an
<input type='button' />
so that I can access it via javascript or jquery. This may not be your case tough.
If you dont want to page load or postback a page when click on asp button, you just have to change a property called CausesValidation to false.
How do I conditionally trigger a full page postback from a link button inside of an update panel?
I have a custom control that contains its own updatepanel with a link button nested inside of it. When the link button is pressed I want its event handler to have the option of either letting the control update as normal or doing a full postback on the page.
Here is the control hierarchy:
Page
Custom Control
UpdatePanel
LinkButton
Event handler Pseudo code:
LinkButton Click Handler Begin
If is a partial post back AND a full postback is needed
Page.DoFullPostback
End If
End Handler
Note: I aways need the partial postback to happen. I was considering injecting a __DoPostback in the controls markup but this seems hacky to me.
Thanks for your help!
Sorry, I'm not familiar with the VB, so my example source will be written in C#:
protected void btnLink_Click(object sender, EventArgs e)
{
bool isAsync = ScriptManager.GetCurrent(Page).IsInAsyncPostBack;
bool postBackIsNeeded = true;
if (isAsync && postBackIsNeeded)
{
ScriptManager.GetCurrent(Page).RegisterPostBackControl(btnClick);
string postback = Page.ClientScript.GetPostBackEventReference(
btnClick,
string.Empty
);
ScriptManager.RegisterStartupScript(
btnClick,
btnClick.GetType(),
"postback",
postback,
true
);
}
}
The main idea is to change the type of postback of your LinkButton control. If neccessary it should be changed to full postback instead of partial during the async postback event. Right after this, another postback script should be generated and it should be executed as soon as the page will be returned to client.
And the last thing - use loop detection condition (if (isAsync && postBackIsNeeded) in my case) otherwise postback will be infinite.
The easiest approach is to create a hidden button somewhere on your page, outside of any UpdatePanels. When you need to do a full postback, use JavaScript to either click the button or issue __doPostback() to it. You can achieve a partial postpack programmatically in JavaScript by calling __doPostback() on an UpdatePanel itself, or to a button inside one.
I am calling my user control in a web page dynamically.
For the first time when I click the button on user control, the event is not firing. When I click the same for a second time, the events are firing..
Can anyone help me?
Sounds like the hookup to the button OnClick event is not occurring on every page load, which is required.
Can you guarantee that the hookup is being performed when you add the control and after a poastback to the page? I always put my event hooks in the Page_Init or Page_Load event handlers and outside of any Postback check. Try putting a breakpoint on the Handler hook up and see if the breakpoint gets "hit" twice.
An event hookup for a button would look similar to:
protected void Page_Load(object sender, EventArgs e)
{
btnSearch.Click += new EventHandler(btnSearch_Click); // breakpoint on this line
}
The client id of the control is derived from the ID of all containing controls that are marked with the INamingContainer interface. So, make sure that ALL controls in the hierarchy have a fixed ID.
For example if you have a Button control inside a Repeater, the ID of the button and the repeater are concatenated to make the client ID for the button. So both the repeater and the button should have the same ID across postbacks.
You can compare the HTML for the first request with the HTML of the second request to quickly determine if this is the problem.
Assign an ID for your dynamically created control -- otherwise no events will be fired.
Are you waiting for the download of full page before pressing the button?
The events are javascript functions hidden by ASP.Net in the page, that maybe not present at the time of your clicking.
I have command button added in my asp.net grids. After performing an action using that button, we refresh the grid to reflect the new data. (basically this action duplicates the grid row).
Now when user refresh the page using F5, an alert message is displayed (to resend the information to server) if we select "retry", the action is repeated automatically.
I know this is a common problem in asp.net, how can we best handle this?
Search for GET after POST - http://en.wikipedia.org/wiki/Post/Redirect/Get - basically, redirect to the current page after you're finished processing your event.
Something like:
Response.Redirect(Request.RawUrl)
If you think you don't need postback paradigm, you might want to look at ASP.NET MVC.
The problem is that asp.net buttons perform form posts when you push a button. If you replace the button with a link your problem should go away. You can also use a button that performs a javascript function that sets the document.location to the address of your page.
If I well understood, you simply have to check if you are in a post-back situation before populating your grid.
Assuming you do that on Page_Load, simply surround the operation with post-back test like this:
private void Page_Load(object sender, EventArgs e)
{
if(!this.IsPostBack)
{
// populate grid
}
}
You need to call response.Redirect(Request.Url.ToString());
or you can wrap the grid with updatepanel and after every command bind the datasource to grid
Inside your <asp:Repeater> tag put this:
EnableViewState="false"
This will cause your control to refresh every time the page loads, no matter if it's a postback or not.
for example:
if you click on 'button' system will catch the event 'button_click'.
if you refresh the page, system will re execute again the same event.
to don t have this problem, in your event insert :
on your event
private void button_click(object sender, System.EventArgs e)
{
button.Enabled =false;
button.Enabled =true;
}
is what you meant?