I need to develop a page which has 2 dropdownlist.
Options of dropdownlist 2 are based on selection of dropdownlist 1.
I have 2 methods to change the dropdownlist 2. What will you choose?
1:
Postback when users select dropdownlist 1 and change dropdownlist 2.
Pros:
Can use the postback feature, can use the asp.net validator
Cons:
Need to communicate with server (more traffic)
Users will see the page loading in the status bar.
2:
Get all the data (not very much data) in a JSON object when loading the page and change the dropdownlist 2 using javascript.
Pros:
Don't need to communicate with server(less traffic)
Cons:
Can't use the postback feature and validator and more troublesome to write server validation.
Also, I usually write the JSON object to the page as follows:
var locations = <asp:Literal runat="server" id="litLocation" text="[]" />
And then set the "litLocation" in page_load after the data is processed by datacontractjsonserializer.
Do you do it in the same way?
I prefer the second option, no need to reload the whole page just to refresh one dropdown list. I'd also do the client side dev in jQuery, much easier. You can do the client side validation for the change event of the first dropdown in jQuery as well, and keep the form submit validation in ASP.NET.
Have a look at the selectChain plugin for jQuery (demo's etc here).
Why not have your javascript call the server when the select box is clicked on, using a GET method, and fill in the select box, using json as the response, then, when an option is picked then fill in the second select box with another ajax request.
This would be scalable, in that if you want to add more options you just change the server, and everything is centralized.
You will need to validate when the form is submitted anyway, as it is possible to change a value of a form to something illegal using some debugging tools, such as Firebug, so never trust anything from a webpage until you have validated it.
So, no point worrying about the validation until the form is actually submitted.
Related
I have a web page and a modal dialog page. On clicking the save button in the show modal dialog. closes the window and returns a value. Now when the
control reaches the JavaScript function of the parent window . I wnt to perform some database operation on the basis of this returned ID.
I am using the following approach to utilize this returned value.
Keeping it in the hidden field and populating the returned value in hidden control.
keeping a hidden button in the parent window, performing the click event when control comes back to JavaScript function of the parent page. Thus in the server side button handler get the value from hidden field and perform database operation on the basis of returned value.
Is this approach fine. Or I can get rid of hidden field
That's not terribly bad provided the ID returned is not sensitive information that someone can use to modify a record that doesn't belong to him. One can perfectly manipulate this ID on the client side for any other ID and have your logic update a different record from what you intended.
If all you are doing is calling a server side method passing this ID; why don't you do the whole update from the pop-window itself (at that point you already know the ID)?
If the parent window (page) is meant to be updated; you can just perform a normal refresh of the page (ie. use window.location to redirect the user to the same page so he can see the update or use Response.Redirect to the same page.)
What you're probably looking for is called AJAX. With AJAX you can communicate with your web server from within your JavaScript code directly. No HTML form posts are required then. You might want to look at frameworks like JQuery. These have easy implementations (cross browser wrappers) to send HTTP requests via AJAX.
Note: I just noticed, you are using ASP.NET. Take a look at ASP.Net AJAX Page Methods.
I'm working on a project where the page load certain controls depending on the index available. The loading occurs in the page load where the method PopulateSearchField is called.
Within this method, all the UserControl are added on the page using : Page.LoadControl("path");
The page load and all the required controls are on the page. My problem is when the user click on the Search button the event is triggered and a query is built based on the user input int those controls. Unfortunately, the method isn't able to produce a proper query as it is unable to find any of the controls on the page.
With a temporary ControlCollection variable, I've been able to see that the number of controls on my page is 3 when it should be something from 4 to 10. Those 3 controls in the collection are the static label and buttons on the page.
I don't know if something is wrong with the code or if it's a page cycle problem as this solution used to work on framework 1.1. Yeah, I know this isn't the best thing to do so, but they did it this way and I gotta make it work.
I'm not sure if it is the migration that has caused the problem or not.
Thanks a lot, David!
When you click the button, the controls are no longer available server side when your click handler is being processed. The page, server side, has no knowledge of the controls you created dynamically since there are no server side controls for the posted values to map to. If you want to find the values, you need to inspect the posted control data and not rely on the server side asp.net control heirarchy.
You could also write all the data you require to a hidden field via javascript and then read the hidden data server side since it will will be posted.
The following is occuring:
Creating controls dynamically
Posting controls data on click
ASP.NET maps the data to the existing controls it knows about.
Your controls are not found so the data is no mapped to anything.
You need to add your controls before the mapping occurs (in PreInit). Check out the Page Lifecycle and you will see how it ties all the controls and data together.
Are you re-adding the controls to the new page when the user clicks search?
Remember... every time the user hits your server for that page... a new Page object is created. If you're dynamically adding controls, you have to do it every time the page loads.
Additionally, since you seem to want to get values out of the controls, you're going to have to make sure that the controls are created with the exact same ID property every time, and created before viewstate is loaded, if you want them to retain their values.
I have a website in ASP.NET (WebForms, NOT MVC) which has a survey form divided in several slides. Each slide has a next button that, obviously does a transition (client-side, not post back or remote request) to the next slide.
In each slide I have several ASP.NET controls with their related validators. I want this validators to be triggered when I click the next button (or maybe when each input loses focus?).
I remembered ASP.NET doing client side validation on lost focus, but maybe I'm wrong... (I quit doing ASP.NET development about 3 years now, so I can't remember)
Thanks
UPDATE:
It would be better to make ASP.NET trigger each validator when the associated control lost focus. I remember ASP.NET doing this (or am I dreaming? =P)
First you need to make sure all of your validators have target controls specified using the "TargetControlID" Attribute on the validators.
Then you can set up a validation group per page and specify the group name in your next button and on the controls themselves.
If you are using regular expression validators you can choose them from this website
To Validate Client Side
If you are using custom validators you can create a client function and specify it on the custom validator using the ClientValidationFunction attribute and by setting EnableclientScript = "true" on the custom validator.
Just be sure your client function has sender and args parameters.
It looks like there's a supplied JavaScript function called Page_ClientValidate which should be callable to check the validation manually from JavaScript. I haven't used it, though, so YMMV.
put all your client-side validators into the same validationgroup and with your 'next' button add the same validation group. When you click the button it will automatically trigger all the validators before it does the post-back.
as to manually triggering the validation...
you might also be able to use ValidatorOnSubmit(). I remember doing this in another project but i'm having a hard time finding the code.
It seems that enabling 'SetFocusOnError' on each validator triggers the validation whenever I try to leave the field.
In short decorate your model, now Data Annotations are supported from Asp.Net 4.5
Check my Answer here..Client side webform validations
I have an aspx page with a set of controls.
A small JS script written on top of jQuery allows the user to drag "li" elements from one list to another.
What I would like now is for my C# code to be able to figure out which items the user has placed in which list after the page is posted back to the server.
Does anyone know how I can do this?
Thanks.
Without some specifics, its hard to get into details. But for ASP.NET server-side controls, the trick is properly maintaining viewstate (or just bypassing it). So strategically you've got two fundamental options:
1) Track the changes server-side by using AJAX to push updates to the server.
2) Track the data client-side by updating some element ASP.NET could understand. My personal favorite is to use a hidden form field that I add a user's "moves" to in a format that can be replayed in my web form.
The easiest way to do it would be to add a HiddenField to your page. Whenever the lists change, populate the HiddenField's value accordingly. When a postback occurs, the HiddenField's value will be available on the server side.
What i've done in the past with drag & drop functionality in ASP.NET, is read the DOM elements via jQuery, and do an AJAX postback with the values in those DOM elements as a parameter.
I'm struggling with an issue I just can find a solution for.
First of all, I can't use asp.net AJAX or anything else thant standard asp.net 2.0 as the server admin won't install anything else.
So here is, what I try to do. (For the curious, skip to the bold question below)
My page consists of several parts, each of which gets loaded by jquery.load(url). One of these page parts gets filled with an aspx that contains a form view. As I don't want to have postbacks, I switch to the EditTemplate of the form view by a simple click on a regular html button that submits a parameter indicating the aspx page to switch to edit mode, e.g.
Page_Load(...)
{
if(Request.Params["SwitchEditMode"]) SwitchEditMode();
}
This works perfectly! Now here the part where I'm stuck. The elements in the EditTemplate are based on a select from a database view and bound to the fields by <%# Bind("xx"). Then I have a html button (no asp control) that submits a parameter to the aspx page that tells it to invoke the DataSource update method. In the dataSource_updating method I look for the controls that contain the values I want to save. But these values are always the same, as when I switch to the edit view. No changes I make in the textboxes or dropdowns are preserved.
A long story short, the question how to save the values from EditTemplate back to the database with jquery?
Up to now I tried several approches, that didn't work out.
In the updating() method look for the controls by FindControl and set e.Command.Parameter["xyz"] = foundcontrol.SelectedValue;. The values are always the same as in the beginning.
Set <asp:parameter name="SampleValue" /> and in the EditTemplate <asp:TextBox Value='<%# Bind("SampleValue")#> The values are always null.
Set a hidden input field with the selected value via javascript. This doesn't work as the control within EditTemplate are only visible after the switch into edit mode
So maybe I'm totally wrong with my ideas, heading into a totally wrong direction and this can be accomplished much easier, but up to now I don't know how to achieve this. I could do it without ajax, but for the user experience I'd prefer the version with jquery.
For all that have read this far and not got confused :-), thanks for your effort!
Best regards,
Andreas
I would forget using a form view and just use a regular html form with regular input controls. Return an object from your web service that has all of your values and populate the controls with ajax and then subjmit with ajax. Either do fully asp.net or fully html/jquery with asmx back end. Otherwise it's just too confusing.
If you load both "modes" of the FormView into the same page using AJAX, you're probably getting duplicate field names. One of them contains the unchanged values which are being saved. How will ASP.NET know the difference? You only want to submit the ones from the EditTemplate, which will require a separate form (or some other hack).
Or perhaps your HTML submit button isn't giving ASP.NET what it needs to repopulate the controls. Are you using ViewState in the page with the FormView?
All in all, this sounds like a hairy combination of technologies... as you well know.