Sunday, July 19, 2009

Ext JS Image Field

Yesterday I spent way too much time on another simple thing in EXT that I would have expected to work out of the box. What I needed was to upload a company logo to a profile and, of course, display that logo in the form. While it's very simple to display an image in a panel or box, it's a totally different thing to display the in image in the form and update it together with other form fields. What I needed is something like this:
and after form submit it should automatically load the new image:
For image upload I used the image upload plugin from EXT examples. To display the image I needed to extend the field component like this:
Ext.form.ImageField = Ext.extend(Ext.form.Field, {
    autoCreate: {tag: 'img'}
    ,setValue: function(new_value){
        if (new_value == undefined || new_value == null) {
            this.el.dom.src = '/images/no_image.png';
        } else {
            this.el.dom.src = '/images/thumbnail/' + new_value;
    ,initValue : function(){

    ,initComponent: function() {
        Ext.apply(this, {



Ext.reg('image_field', Ext.form.ImageField);

This is a bit simplified version as I removed the rails specific code, but anyway the main points are here:
line 2 creates image tag (rather than the default text field tag)
line 5 defaults the image src property to a placeholder (in case there's no image uploaded)
line 7 - in case there is a valid image it will change the src path to that image - in my case it's routed to Images controller and action thumbnail which returns a downscaled version of the image.
Other than this don't forget to set the FormPanel's fileUpload: true and refresh the form on submit success. I usually send the updated object JSON in the response to update action.:
  def update
    contact = Contact.find(params[:id])
    success =
    contact = Contact.find( if success"saved")
    respond_to do |format|
      format.ext_json do
        json = contact.to_ext_json(:success => success,
                                   :methods => [:image_id],
                                   :includes => [:address],
                                   :messages => {:notice => l(:contact_updated), :warning => l(:contact_update_error)})
        render :json => json #:json => {:success => success}
        headers["Content-Type" ] = "text/html"

!!!Notice line 16 - you have to manually set the content type to "text/html" because rails will default to "text/javascript" which will not work with file uploads!!! It works with fileUpload: false but it doesn't with fileUpload: true. I don't really know if Rails or EXT is right here but did take me some time to figure this out.
this will produce the following JSON (I removed the unnecessary fields):
{"success": true,
    "messages": {"notice": "Contact was successfully updated.", "warning": "contact_update_error"},
    "data": {"contact[image_id]": 15, "contact[active]": false, "contact[client_account_id]": 2, "contact[client_account_no]": "100",
        "contact[created_at]": "2009-07-07T10:31:54+08:00", "contact[credit_term_id]": 1}}
Now in the forms success method I can use the to update the form:
success: function(form, action) {


  1. Tried this however it doesn't work to well on a ViewPort layout nested within TabPanels, the ImageField always duplicates itself when you flip between the two. Otherwise just using it within a window it works fine.

  2. Thanks for the example, saved me some work.

    One small improvement, if you need to use more than 1 in a form, or as I did. different images in different forms in a tab panel the you need to change

    autoCreate: {tag: 'img'}


    defaultAutoCreate: { tag:'img' }

    otherwise all the images share the same dom element and only 1 changes when the data for any form changes.