Im trying to add buttons to a placeholder, each with an eventhandler to the same method.
if (!this.IsPostBack)
{
foreach (Entry ent in results)
{
HtmlButton btn = new HtmlButton();
btn.ServerClick += new EventHandler(resultSelected);
btn.InnerText = ent.name;
btn.ID = ent.ID.ToString();
PlaceHolder1.Controls.Add(btn);
}
}
1)
The button is added to the page but when its clicked the method (resultSelected) is not called, only Page_Load again. And when it enters Page_Load the PlaceHolder is empty (the button is not displayed on the page). How do I accomplish what Ive tried to do?
2) How do I assign CSS classes to buttons created in this way?
It's quite common issue when you start working with ASP.NET for the first time - adding dynamic controls on server side.
First thing is that You have to add those controls and assign eventhandler on every page request - on every postback as well. For proper event handling and restoring ViewState, you have to assign to them the same IDs and apply the same hierarchy.
Controls needs to be added before Page Load event - most convinient would be adding them on in overriden CreateChildControls() method, which is fired on Postback before OnLoad method.
Events are fired after OnLoaded method, so if you will create any control in for example OnPreRender/Render method - any event won't be fired.
This is most straightforward approach with some details skipped in my description. For more detailed information please read about ASP.NET Application Life Cycle.
As for the second part of your question, you can either use explicit styles setting with Style Property or it should be also possible to add class attribute using Attributes Property, but right now i'm guessing, cause i think HtmlButton doesn't have CssClass property.
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 am using web forms to develop a web application.
From the very beginning, I have always been surprised by the page_load event being fired twice, and finally today I found out that all gridviews and texts are rendered after first page_load, and it takes another page_load to render all the dynamic asp.net charts..
why is it so, is there an attribute on the chart web server control that I can use to bypass this?
Check to see if you "AutoEventWireup" set to true. If this is a control, check the parent control/page also. Even if the control itself is set to false, but the parent is set to true, it seems to fire anyway.
Also check where you assign listener to Page_Load event:
this.Load += new System.EventHandler(this.Page_Load);
Should be in InitializeComponent method
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 have an ASP.NET web form which I am adding a variable number User Controls to. I have two problems:
The User Controls are added to a PlaceHolder on the form in the first PageLoad event (I only add them when "(!this.IsPostback)", but then when the form is posted back, the controls are gone. Is this normal? Since other controls on the form keep their state, I would expect these dynamically added ones to stay on the form as well. Do I have to add them for every postback?
I also have a button and an event handler for the button click event, but this event handler is never called when I click on the button. Is there something special I have to do to catch events on dynamically added controls?
Yes, you need to add them in every postback.
Yes... the control needs to be in the control hierarchy before asp.net dispatches the event (i.e. create the dynamic controls as early in the page lifecycle as possible).
1) You should add the controls on the Pre-init (Page life cycle)
2) You have to attach the event handler to the event of the created button.(events might occur much later in the page life cycle than the same events for controls created declaratively)
To achieve this, add your controls at page init instead of page load. (re-add at postback)
You'll need to know the id of the buttons added to bind them to the event.
I ran into a similar problem. I had a page that displayed a collection of custom web controls. My solution was to add an additional invisible web control so that when I clicked a button to add another control that I would just use the invisible one. Then on post back my load function would add another invisible control to the collection.
I figured out yesterday that you can actually make your app work like normal by loading the control tree right after the loadviewstateevent is fired. if you override the loadviewstate event, call mybase.loadviewstate and then put your own code to regenerate the controls right after it, the values for those controls will be available on page load. In one of my apps I use a viewstate field to hold the ID or the array info that can be used to recreate those controls.
Protected Overrides Sub LoadViewState(ByVal savedState As Object)
MyBase.LoadViewState(savedState)
If IsPostBack Then
CreateMyControls()
End If
End Sub
I ran into the exact same problem and struggled through like 5-6 hours.
I'm posting this maybe someone like me could get help.
1) You should initialize your controls at Page.PreInit event. (In my case I had to add my controls to a place holder so I extended PreInit to load those controls before but you don't need to do that. It depends on your scenario.)
2) You should bind those exact methods to your controls after you initialize them in your Page.PreInit event.
Here is my sample code:
protected override void OnPreInit(EventArgs e)
{
// Loading controls...
this.PrepareChildControlsDuringPreInit();
// Getting ddl container from session and creating them...
if (GetDDLSession().Count != 0)
{
foreach (DropDownList ddl in GetDDLSession())
{
ddl.SelectedIndexChanged += SelectedIndexChanged;
phDropDowns.Controls.Add(ddl);
}
}
base.OnPreInit(e);
}
public static void PrepareChildControlsDuringPreInit(this Page page)
{
// Walk up the master page chain and tickle the getter on each one
MasterPage master = page.Master;
while (master != null) master = master.Master;
}
I am trying to build a server control that, depending on a "QuestionTypeId" display either a text box, date picker or Yes-No radio buttons.
I have my control displaying how I want it to, but when the submit button is pressed on the form, the text box, date picker or radio buttons that were generated in the RenderContents method are all null.
I have attempted to store the generated controls in view state, that stopped them being null, but the user inputs were not being stored.
I will post code if it is needed. Just ask.
I think you need to create (and add) the controls in CreateChildControls. This will mean you'll need to store the value of the QuestionTypeId in either Viewstate or ControlState (I'd argue that ControlState is applicable in this case, as your control can't work without this value).
When you add controls dynamically, you need to make sure they are recreated before the viewstate is restored.
I haven't done this in a while, but from memory I think you should recreate your controls in the OnInit method. This happens before postback data has been loaded and before the controls have their values set from viewstate.
It may be worth doing some reading on the asp.net page lifecycle:
http://msdn.microsoft.com/en-us/library/ms178472.aspx
You can create a user control and use server controls for textbox, datepicker, radiobuttons.
If you create a cusom server control then you have to add the posted data to your control properties. You can do this at your control OnInit event:
MyProperty = Request.Form("myControl");
A simpler method would be to create all the controls at design time and make the controls invisible based on you requirements.
Example code:
protected void Page_Load(object sender, EventArgs e)
{
txtBox.Visible = QuestionTypeID == 1;
chkBox.Visible = QuestionTypeID == 2;
}
If you do use dynamic controls you should do as David pointed out, save the value QuestionTypeID in ViewState or ControlState and then create the control you want based on that value.
(the control needs to be created every time the page loads even on a post back and they cannot be created later in the page life cycle then the Page_Load method if you want their ViewState persisted and recovered)
Example code:
protected void Page_Load(object sender, EventArgs e)
{
var questionId = ViewState["QuestionTypeID"];
if(questionId == /* Value to create TextBox */) {
var txt = new TextBox { ID = "txt" };
placeHolder.Controls.Add(txt);
} else if(questionId == /* Value to create Calender */) {
var cal = new Calender { ID = "cal" };
placeHolder.Controls.Add(cal);
}
/* Once the controls are added they will be populated with the posted values */
}
P.S.
It's always a good idea with dynamic controls to specify the ID.
You can save the added controls to member variables and use them elsewhere (after they are assigned)
You can subscribe to their events and if the user posted a new value your method will be called
I have followed your advice and done the following:
1) Question Type is stored in view state in my server control.
2) on CreateChildControls now creates a new instance of my control and adds it to a place holder on the page.
My problem now is that things seem to fire in bit of an odd order:
1)On initial load of page, create child controls is fired and the RenderContents method of my server control fires.
2)A button is clicked to load a new contact, this triggers create child controls and RenderContents is fired.
3)details are entered and save is pressed, this triggers Create Child Controls but RenderContents is not triggered and a NullReferenceException is generated by trying to access my control to get the value out. (If i skip the code that access my controls, RenderContents is called and renders.
Seconly, another issue is that when I try an set a value (onDataBind) I try to access the Text box that has been generated in my server control and get another NullReferanceExeption
Thoughts?