I want to generate a drop down list from another drop down list. That is I have a dropdown of countries. When selecting a country,another dropdown must come with values as states of that specific country. How to do that in asp.net using c#?
for each country you have, add a new list item to the drop down list, with text the country and the value some id of the country. On the second drop down list, set the auto post back property to true and add an event to the on selected item change. In the event code, get the selected item and by the second ddl.
Try it!
Tip: add a hidden field on the page, and on the selected item changed event from the first ddl, set the value of the hidden field, the selected value. On the page_load event, verify if the value is string.empty and if is an id in the value. If it is, bind the second ddl.
The technology you're looking for is called a Cascading Dropdown.
If you are using WebForms then Ajax Control Toolkit then this has one built in:
http://www.asp.net/ajaxLibrary/AjaxControlToolkitSampleSite/CascadingDropDown/CascadingDropDown.aspx
Otherwise you might need to do a further search if you are using MVC.
PS I'm not particularly proud of posting a link to the Ajax Control Toolkit as its not the best library out there but it is an easy drop in for what you want. If you're serious about doing a good job then I'd search for better options for cascading dropdowns.
Related
I have 3 drop-down lists on my page and a data-list. All of them are populated from SQL database based on selected item from previous drop-down.
AutoPostBack is set to true on all three dropdowns, and on first page load they are displayed correctly i.e. on all three dropdowns first item is selected and the result is displayed in data-list based on that selection. But when I change selection in the first drop-down, only second drop-down gets updated (sometimes it updates the third but its inconsistent), and to get the update on the third one I need to change the selection on the second one. The result in data-list mostly remains the same, and updates when I change selection in third drop-down.
What do I need to do to get the data-list updated when I change the selection in first drop down?
Withoug looking at your code it is difficult to answer the question. But by looking at the description of your question, it looks like you are setting AutoPostBack=true, but not handling the OnSelectedIndexChanged event.
First of all you should add OnSelectedIndexChanged event for all the three dropdowns like below.
protected void dropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
}
In each selectedindex changed event, you need to bind the next dropdown lists.
May be you can have one common function for binding the list view, which you need to call in each SelectedIndexChanged event.
If you just set AutoPostBack=true and not handling the selectedindex changed, then it does not work properly as expected
To get the data-list updated when the first drop-down is changed, you must fire the post-back event manually(for the second and 3rd drop-downs)!
Assuming the data on the 3rd drop-down is based on the selection from the 2nd,on the client Page in JavaScript : Try to have the first item or a default item selected. This would populate the 3rd list.
A good practice would be to have a default element, that is not specific!
It is also a matter of design. If its a typical list where the second and 3rd lists would be changed often locally, then it is best to have it pre-fetched and stored in a local Json object!
to get the list populated on the selection_index changed of the first dropdown change. Call the populating method of the other two dropdown lists...
and on the selection_change event of the second dropdown call the populating method of the third dropdown
Check your selectedIndexchanged method and whenever you are binding data to datalist before that clear the datalist items and then do binding. so you could have clear idea which data is not populating. and post your code here so it wolud give a clear idea
Lets say I have three DropDownList controls in a web user control and they depend on each other.
Categories
Brands
Products
Explanation:
After I choose a category from Categories dropdown list, related brands are loaded in Brands DropDownList and same happens when I choose specific brand and they are all located in a web user control since I am using it too much on different pages, I don't want to copy and paste the same code on all the pages.
Problem: The pages can contain a GridView and DataSource control which needs an additional Where parameter to fetch all the data needed in and that parameter could depend on selected product within the Products DropDownList control.
Question: So how can I get that Selected Product Value from Products DropDownList to bind it to SQLDataSource or any other DataSource control.
My Thoughts: I belive I can solve this problem in the ways following.
I can use static variable which is updated once Products selected. That field variable could be public so everyone can reach it
Selected Products DropDownList can create a QueryString Field for me to grap the selected value.
In the same way, the dropdownlist can create a Session variable on the fly and I can fetch the value
It can create a hidden field maybe.
But: Well those are some of my thoughts but I found them so naive to implement. I need something elegant and satisfying to solve this problem. It should be something like a gateway from the Web User Control to outside world.
Maybe a separate class or a Property can help me in the gateway solution.
Anyways, I am waiting for your answers.
If I'm understanding the question correctly:
You can add a property to the user control that exposes the products DDL selected value.
You can also add and raise an event from the user control that fires when the products DDL selected value changes. Creating a custom event argument that contains the product value, allows it to get passed directly to the event handler.
Then your pages can handle the event raised by the user control, have the product value, and bind the grid.
You could bind the DropDownList.SelectedIndexChanged events to the same function, and test the SelectedValue properties of each DropDownList. If their SelectedValues are valid, bind the grid to your DataSource.
I've done this in the past when I needed users to input a certain amount of data before I could query the database. I set the Hidden property on my GridView if the DropDownLists weren't valid, and reset it when they were properly bound.
The basic problem: selecting a few items from a list of thousands.
The potential solution:
I have an autocomplete field that searches the db, and returns a name/id pair. This is working fine.
The next step is to preserve the selected IDs, and allow the user to remove some if needed. For this, I've been looking at using a select, and was hoping a UI something like that provided by this, but it doesn't work: it allows you to select items that already exist in the select, but doesn't work with a dynamically created select.
The final step is a traditional postback (using a submit button, this is in asp.net webforms) where I'll need to have access to the final list of IDs.
Are there other options for this?
Based on your comments below, there are a lot of ways to skin this cat. The following approach is similar to the SelectList idea only it doesn't use a dropdown list. The nice thing about the Listbox versus the DropdownList is that the user will be able to view many items at once. Of course, the choice of using a Listbox or a DropdownList doesn't really matter as they both essentially provide the same functionality. The key about this answer is that values are stored on the client until you're ready to submit.
Create an autocomplete textbox that dynamically fills a Listbox as you type.
Clicking on a Listbox item results in two things happeing:
The ID of the selected item is stored in a client-side array
A list of items are rendered/re-rendered on the page exactly like the SelectList. Clicking the red 'X' will remove the ID from the array and re-render the list. You'll have to do a bit of jQuery coding on your side but it isn't much.
The above steps are repeated until the user has selected all of their items.
Upon clicking "Save", only the selected items are submitted to the server for processsing.
I have the following scenario.
I have a search page which is split into two divs. In the first, a user can create query parameters using a range of drop down menus. In the second div a user can enter text to source the query parameter and narrow the search further. On the drop down selectedindex change event, a radio button is selected indicating which search is being looked at.
i.e.
div1 div2
ddl1 tbx1
ddl2 ddl4
ddl3
rad1 rad2
Based upon their selection, the user can then click a button, btnReturn, that returns the query.
So therefore, I have the following questions.
If I have a range of drop downs, in div1, what sort of validation do I need to set up so that at least one of these drop downs needs to be selected in order for a query to be selected. I cannae just put in required fields as not all of these fields are required, a minium of one of these is need to product a reasonable search.
I am assuming I can do all of this using .net validation?
I am thinking I can use Validation Groups for div1 & div2 but is it possible to assign both groups to one control i.e. btn click? Is it a case of doing the last part programmatically?
And that concludes today's essay! any help, as always, greatly appreciated.
Create a user control (or custom control) wrapping all dropdowns. Then create a Custom Validator, set its validated control to the wrapper you created. Write a javascript function to check that at least one value is selected in the dropdowns and set the ClientValidationFunction property of the custom validator to use it.
Yes.
No, this wouldn't work in your case (unless you want a postback when switching between the DIVs). Create two submit buttons, and hide them on the client depending on the selected DIV.
Can anyone tell me how to populate one listbox from another listbox item using JavaScript or ASP.NET 2.0?
Duplicate
How would I move one list box items to another listbox items in JavaScript?
For ex--My 1st listbox is Region then accourding to region selection the second listbox country will be display and accourding to country seletion state listbox will display all will come from database depends on Region Id or Country id n all
You may be interested in the 'Cascading Dropdown' control from the ASP.net AJAX Control Toolkit. http://www.asp.net/AJAX/AjaxControlToolkit/Samples/CascadingDropDown/CascadingDropDown.aspx
You could also probably do this without the toolkit, using the standard UpdatePanel from ASP.net AJAX and specifing the "onChange" event of the first dropdown as a "trigger" for that UpdatePanel to be updated. Be sure you set AutoPostback="true" on the dropdown so it is fired properly is you go this route also.
Your question leaves out a lot of detail, but basically you would wire a function to the onchange event of the first listbox, that would populate the second listbox. If the contents would need to be dynamically loaded, you would then need to use AJAX (or similar) to pull them from the server and push them into the second box; alternatively if your contents are statically defined and not too weighty, it would be more responsive to serve them with the original document (perhaps as an associative array keyed on the values of the first listbox) and then update the second listbox based on an array lookup.