Adding dynamic form elements using AHAH

I have the example above copied almost line for line except step 9.

When I do the ahah submit the first time, I get the following message without the return value I specified:
Page test has been updated.

Then, every submit after that I get the return value and the message:
This content has been modified by another user, changes cannot be saved.

Any idea what I could be doing wrong?

Also, the ahah bits are part of a custom CCK widget. Don't know if that matters.

Say you've defined your own content type and you'd like to manipulate an element on the node add form using AHAH. In my case, I want to change the value in a textfield based on the value of another element.

The process is:
1. Create a CCK field whose value you want to change.
2. Force drupal to cache your form (in hook_form_alter)
3. Create your menu item (in hook_menu)
4. Link to the menu url in your ahah property of the element you want to trigger the change
5. Write a function to change the value of the element, and make sure that gets stored in $form

Say that we want to change the value of field_flowers to "roses" when a button is clicked (yes, it's a pretty arbitrary example, but the logic will apply for changing the value of any other form element based on an AHAH event). Fleshing out each of the above steps:

1. Create a CCK field whose value you want to change.
In admin/content/types choose the CCK content type you want to work with, and add a text field - call it field_flower. We'll be assigning it the value of 'roses' later.

2. Force drupal to cache your form (in hook_form_alter) by putting a $form['#cache'] = TRUE; in the relevant spot, like so:

We force drupal to cache the form because it doesn't for a node add form. Once we've clicked on the element which triggers the change, we need to access $form and change some things within it - and we can only access $form if it's cached.

3. Create your menu item (in hook_menu)

4. Link to the menu url in your ahah property of the element you want to trigger the change

In your hook_form_alter() function, add the following (after the $form['#cache'] = TRUE; line):

In this case we've added AHAH to a new button (called 'field_my_button') and asked it to load up the url 'ahah-change-flower' (which is loaded in the background because that's the nature of AHAH - it's not a full page reload). Once that url is requested drupal calls the function mymodule_change_flower() - which is our next step.

Note that the value of 'wrapper' is the id of the div which field_flower sits in. To find the value of that particular id, view the source code of your form and look for field_flower. Firebug is your friend!

5. Write a function to change the value of the element, and make sure that gets stored in $form

Somewhere in your module, add this:

Note how similar this code is to the 9 steps above, yet also different. Firstly, since we're adding or editing a content type, we need to include the relevant form generating function, which is in node.pages.inc (the function is called node_form() if you're interested).

Note that step 5 and step 6/7/8 are commented out - we don't need them. I found that executing these is unnecessary and actually removes the values I want to access in $form. Simply retrieving $form from the cache is enough to make the changes; then save $form to the cache again, rebuild the form, and render it.

This code was taken from Wim Leers post on his AHAH helper module, about why AHAH in drupal is so hard.

6. Summary
So what we've done is set field_flower to the value of "roses" when a button is clicked. Equally, we could change the value of field_flower if we were change the value of a select list, by attaching the #ahah property to the relevant select list.

This logic will work for most CCK field types, but it doesn't work for what I originally researched this for: changing the values in a node reference select list when another element's values change. I hope to find a solution for that soon!

.

In the fapi reference, it is said that #ahah can react to a 'change' event. So I understand that I could use '#ahah" on a select.
But there is no '#submit' options for selects, so I understand that it will use the default submit handler, which would submit the form, which is obviously not what is wanted.

Are there any examples of AHAH with selects around ?
Or is it just an inconsistency, meaning that AHAH can't be used with a change event ?

I have a little problem with "form building function should create subsequent steps based on the contents of $form_state" part:
when rebuilding the form while processing the ahah callback function my form building function receives no 'values' in $form_state.
here's the code for form building:

As you can note, I'm adding the current value of $form_state after my wrapper element. During callback execution I'm getting following $form_state data:

array ( 'storage' => NULL, 'submitted' => false, 'post' => array ( ), )

And here's the code for ahah callback:

Thanks for this great tutorial, it works really great and it helped me building very nice features.

Just one problem that only occures rarely and I don't know why that happens while 99% of the time the very same code works without an error at all. When preparing for #5 there are the following two lines of code:

and the second fires an error message that a wrong parameter has been used. Is suspect, that in that case $form['#parameters'] hasn't been an array. However, on the site where this happaned once or twice, there is only one single form which makes use of ahah and it usually works without that error. In other words, that variable seems to be an array but not always.

I know that sounds crazy but that's what happened. Any idea?

Hello, First of all GREAT Tutorial, I am very new to Drupal. I would like to add that I am very impressed with the community. I have a Form using AHAH with a callback that performs a search of an external database table and displays the results in a div wrapper. All this works great when I click the submit button. Once the results are displayed the pagination is at bottom (from pager_query) like expected but when I click any page number, it just displays the single line of code accross the top of browser: "{ "status": true, "data": "\x3cfieldset\x3e\x3cdiv\x3e\n \x3ctable class=..........."

I have done a var_dump of the form values and everything looks ok from the cache, including the form_id and form_build_id.

The resulting line is correct, it just needs to be written to my div wrapper below my form just like when I click submit the first time.

Here is my callback:

Here is my submit button in my form:

Thank you for any help that anyone can provide and for your time in advance.

When drupal_process_form is called, what submit handlers will be called? I have a small example (included below), which is a select element with an ahah binding, as well as a few submit buttons. The submit handler that gets called when the select is changed is the first one declared in code. This doesn't seem right. What if I had two ahah select elements. They call the same function! Maybe there is something I don't understand. If I switch the order of the two submit buttons, then submit_b is called. Please examine the code, and let me know what I am overlooking here.

Also, looking at the quicktabs module, I see that the submit handlers use these lines near the tops of the functions:

Thanks