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Odoo 13开发者文档：自定义网页客户端

Alan
本文来自Odoo 13官方文档之开发者文档系列文章
注：本节是真的真的很老了。它会在某天进行更新，但此时学习本课程可能会让人不悦，因为写的时间太早了。本指南有关为Odoo客户端创建模块。要通过Odoo创建网站，请参见, 构造网站；要添加业务功能或继承Odoo的业务系统，请参见构建模块。

一个简单模块

我们先创建一个包含基本网页配置的Odoo模块并测试其web框架。

示例模块可在线获取，通过如下命令即可下载：

执行以上命令时将创建一个petstore 文件夹。然后需要在Odoo的 addons path下添加该文件夹、新建一个数据库并安装 oepetstore 模块。

如果查看petstore文件夹，将看到如下内容：

The module already holds various server customizations. We’ll come back to these later, for now let’s focus on the web-related content, in the static folder.

Files used in the “web” side of an Odoo module must be placed in a static folder so they are available to a web browser, files outside that folder can not be fetched by browsers. The src/css, src/js and src/xml sub-folders are conventional and not strictly necessary.

oepetstore/static/css/petstore.css
Currently empty, will hold the CSS for pet store content
oepetstore/static/xml/petstore.xml
Mostly empty, will hold QWeb templates
oepetstore/static/js/petstore.js
The most important (and interesting) part, contains the logic of the application (or at least its web-browser side) as javascript. It should currently look like:

Which only prints a small message in the browser’s console.

The files in the static folder, need to be defined within the module in order for them to be loaded correctly. Everything in src/xml is defined in __manifest__.py while the contents of src/css and src/js are defined in petstore.xml, or a similar file.

Odoo JavaScript Module

Javascript doesn’t have built-in modules. As a result variables defined in different files are all mashed together and may conflict. This has given rise to various module patterns used to build clean namespaces and limit risks of naming conflicts.

The Odoo framework uses one such pattern to define modules within web addons, in order to both namespace code and correctly order its loading.

oepetstore/static/js/petstore.js contains a module declaration:

In Odoo web, modules are declared as functions set on the global odoo variable. The function’s name must be the same as the addon (in this case oepetstore) so the framework can find it, and automatically initialize it.

When the web client loads your module it will call the root function and provide two parameters:

  • the first parameter is the current instance of the Odoo web client, it gives access to various capabilities defined by the Odoo (translations, network services) as well as objects defined by the core or by other modules.
  • the second parameter is your own local namespace automatically created by the web client. Objects and variables which should be accessible from outside your module (either because the Odoo web client needs to call them or because others may want to customize them) should be set inside that namespace.

Classes

Much as modules, and contrary to most object-oriented languages, javascript does not build in classes1 although it provides roughly equivalent (if lower-level and more verbose) mechanisms.

For simplicity and developer-friendliness Odoo web provides a class system based on John Resig’s Simple JavaScript Inheritance.

New classes are defined by calling the extend() method of odoo.web.Class():

The extend() method takes a dictionary describing the new class’s content (methods and static attributes). In this case, it will only have a say_hello method which takes no parameters.

Classes are instantiated using the new operator:

And attributes of the instance can be accessed via this:

Classes can provide an initializer to perform the initial setup of the instance, by defining an init() method. The initializer receives the parameters passed when using the new operator:

It is also possible to create subclasses from existing (used-defined) classes by calling extend() on the parent class, as is done to subclass Class():

When overriding a method using inheritance, you can use this._super() to call the original method:

Widgets Basics

The Odoo web client bundles jQuery for easy DOM manipulation. It is useful and provides a better API than standard W3C DOM2, but insufficient to structure complex applications leading to difficult maintenance.

Much like object-oriented desktop UI toolkits (e.g. Qt, Cocoa or GTK), Odoo Web makes specific components responsible for sections of a page. In Odoo web, the base for such components is the Widget() class, a component specialized in handling a page section and displaying information for the user.

Your First Widget

The initial demonstration module already provides a basic widget:

It extends Widget() and overrides the standard method start(), which — much like the previous MyClass — does little for now.

This line at the end of the file:

registers our basic widget as a client action. Client actions will be explained later, for now this is just what allows our widget to be called and displayed when we select the Pet Store ‣ Pet Store ‣ Home Page menu.

Display Content

Widgets have a number of methods and features, but the basics are simple:

  • set up a widget
  • format the widget’s data
  • display the widget

The HomePage widget already has a start() method. That method is part of the normal widget lifecycle and automatically called once the widget is inserted in the page. We can use it to display some content.

All widgets have a $el which represents the section of page they’re in charge of (as a jQuery object). Widget content should be inserted there. By default, $el is an empty <div> element.

A <div> element is usually invisible to the user if it has no content (or without specific styles giving it a size) which is why nothing is displayed on the page when HomePage is launched.

Let’s add some content to the widget’s root element, using jQuery:

That message will now appear when you open Pet Store ‣ Pet Store ‣ Home Page

The HomePage widget is used by Odoo Web and managed automatically. To learn how to use a widget “from scratch” let’s create a new one:

We can now add our GreetingsWidget to the HomePage by using the GreetingsWidget’s appendTo() method:

  • HomePage first adds its own content to its DOM root
  • HomePage then instantiates GreetingsWidget
  • Finally it tells GreetingsWidget where to insert itself, delegating part of its $el to the GreetingsWidget.

When the appendTo() method is called, it asks the widget to insert itself at the specified position and to display its content. The start() method will be called during the call to appendTo().

To see what happens under the displayed interface, we will use the browser’s DOM Explorer. But first let’s alter our widgets slightly so we can more easily find where they are, by adding a class to their root elements:

If you can find the relevant section of the DOM (right-click on the text then Inspect Element), it should look like this:

Which clearly shows the two <div> elements automatically created by Widget(), because we added some classes on them.

We can also see the two message-holding divs we added ourselves

Finally, note the <div class="oe_petstore_greetings"> element which represents the GreetingsWidget instance is inside the <div class="oe_petstore_homepage"> which represents the HomePage instance, since we appended

Widget Parents and Children

In the previous part, we instantiated a widget using this syntax:

The first argument is this, which in that case was a HomePage instance. This tells the widget being created which other widget is its parent.

As we’ve seen, widgets are usually inserted in the DOM by another widget and inside that other widget’s root element. This means most widgets are “part” of another widget, and exist on behalf of it. We call the container the parent, and the contained widget the child.

Due to multiple technical and conceptual reasons, it is necessary for a widget to know who is its parent and who are its children.

getParent()
can be used to get the parent of a widget:
getChildren()
can be used to get a list of its children:

When overriding the init() method of a widget it is of the utmost importance to pass the parent to the this._super() call, otherwise the relation will not be set up correctly:

Finally, if a widget does not have a parent (e.g. because it’s the root widget of the application), null can be provided as parent:

Destroying Widgets

If you can display content to your users, you should also be able to erase it. This is done via the destroy() method:

When a widget is destroyed it will first call destroy() on all its children. Then it erases itself from the DOM. If you have set up permanent structures in init() or start() which must be explicitly cleaned up (because the garbage collector will not handle them), you can override destroy().

The QWeb Template Engine

In the previous section we added content to our widgets by directly manipulating (and adding to) their DOM:

This allows generating and displaying any type of content, but gets unwieldy when generating significant amounts of DOM (lots of duplication, quoting issues, …)

As many other environments, Odoo’s solution is to use a template engine. Odoo’s template engine is called QWeb.

QWeb is an XML-based templating language, similar to Genshi, Thymeleaf or Facelets. It has the following characteristics:

  • It’s implemented fully in JavaScript and rendered in the browser
  • Each template file (XML files) contains multiple templates
  • It has special support in Odoo Web’s Widget(), though it can be used outside of Odoo’s web client (and it’s possible to use Widget() without relying on QWeb)

Using QWeb

First let’s define a simple QWeb template in the almost-empty oepetstore/static/src/xml/petstore.xml file:

Now we can use this template inside of the HomePage widget. Using the QWeb loader variable defined at the top of the page, we can call to the template defined in the XML file:

QWeb.render() looks for the specified template, renders it to a string and returns the result.

However, because Widget() has special integration for QWeb the template can be set directly on the widget via its template attribute:

Although the result looks similar, there are two differences between these usages:

  • with the second version, the template is rendered right before start() is called
  • in the first version the template’s content is added to the widget’s root element, whereas in the second version the template’s root element is directly set as the widget’s root element. Which is why the “greetings” sub-widget also gets a red background

QWeb Context

QWeb templates can be given data and can contain basic display logic.

For explicit calls to QWeb.render(), the template data is passed as second parameter:

with the template modified to:

will result in:

When using Widget()’s integration it is not possible to provide additional data to the template. The template will be given a single widget context variable, referencing the widget being rendered right before start() is called (the widget’s state will essentially be that set up by init()):

Result:

Template Declaration

We’ve seen how to render QWeb templates, let’s now see the syntax of the templates themselves.

A QWeb template is composed of regular XML mixed with QWeb directives. A QWeb directive is declared with XML attributes starting with t-.

The most basic directive is t-name, used to declare new templates in a template file:

t-name takes the name of the template being defined, and declares that it can be called using QWeb.render(). It can only be used at the top-level of a template file.

Escaping

The t-esc directive can be used to output text:

It takes a Javascript expression which is evaluated, the result of the expression is then HTML-escaped and inserted in the document. Since it’s an expression it’s possible to provide just a variable name as above, or a more complex expression like a computation:

or method calls:

Outputting HTML

To inject HTML in the page being rendered, use t-raw. Like t-esc it takes an arbitrary Javascript expression as parameter, but it does not perform an HTML-escape step.

Conditionals

QWeb can have conditional blocks using t-if. The directive takes an arbitrary expression, if the expression is falsy (false, null, 0 or an empty string) the whole block is suppressed, otherwise it is displayed.

Iteration

To iterate on a list, use t-foreach and t-as. t-foreach takes an expression returning a list to iterate on t-as takes a variable name to bind to each item during iteration.

Defining attributes

QWeb provides two related directives to define computed attributes: t-att-name and t-attf-name. In either case, name is the name of the attribute to create (e.g. t-att-id defines the attribute id after rendering).

t-att- takes a javascript expression whose result is set as the attribute’s value, it is most useful if all of the attribute’s value is computed:

t-attf- takes a format string. A format string is literal text with interpolation blocks inside, an interpolation block is a javascript expression between {{ and }}, which will be replaced by the result of the expression. It is most useful for attributes which are partially literal and partially computed such as a class:

Calling other templates

Templates can be split into sub-templates (for simplicity, maintainability, reusability or to avoid excessive markup nesting).

This is done using the t-call directive, which takes the name of the template to render:

rendering the A template will result in:

Sub-templates inherit the rendering context of their caller.

To Learn More About QWeb

For a QWeb reference, see QWeb.

Exercise

Widget Helpers

Widget’s jQuery Selector

Selecting DOM elements within a widget can be performed by calling the find() method on the widget’s DOM root:

But because it’s a common operation, Widget() provides an equivalent shortcut through the $() method:

Easier DOM Events Binding

We have previously bound DOM events using normal jQuery event handlers (e.g. .click() or .change()) on widget elements:

While this works it has a few issues:

  1. it is rather verbose
  2. it does not support replacing the widget’s root element at runtime as the binding is only performed when start() is run (during widget initialization)
  3. it requires dealing with this-binding issues

Widgets thus provide a shortcut to DOM event binding via events:

events is an object (mapping) of an event to the function or method to call when the event is triggered:

  • the key is an event name, possibly refined with a CSS selector in which case only if the event happens on a selected sub-element will the function or method run: click will handle all clicks within the widget, but click .my_button will only handle clicks in elements bearing the my_button class
  • the value is the action to perform when the event is triggeredIt can be either a function:

    or the name of a method on the object (see example above).

    In either case, the this is the widget instance and the handler is given a single parameter, the jQuery event object for the event.

Widget Events and Properties

Events

Widgets provide an event system (separate from the DOM/jQuery event system described above): a widget can fire events on itself, and other widgets (or itself) can bind themselves and listen for these events:

This widget acts as a facade, transforming user input (through DOM events) into a documentable internal event to which parent widgets can bind themselves.

trigger() takes the name of the event to trigger as its first (mandatory) argument, any further arguments are treated as event data and passed directly to listeners.

We can then set up a parent event instantiating our generic widget and listening to the user_chose event using on():

on() binds a function to be called when the event identified by event_name is. The func argument is the function to call and object is the object to which that function is related if it is a method. The bound function will be called with the additional arguments of trigger() if it has any. Example:

Properties

Properties are very similar to normal object attributes in that they allow storing data on a widget instance, however they have the additional feature that they trigger events when set:

  • set() sets the value of a property and triggers change:propname (where propname is the property name passed as first parameter to set()) and change
  • get() retrieves the value of a property.

Exercise

Modify existing widgets and classes

The class system of the Odoo web framework allows direct modification of existing classes using the include() method:

This system is similar to the inheritance mechanism, except it will alter the target class in-place instead of creating a new class.

In that case, this._super() will call the original implementation of a method being replaced/redefined. If the class already had sub-classes, all calls to this._super() in sub-classes will call the new implementations defined in the call to include(). This will also work if some instances of the class (or of any of its sub-classes) were created prior to the call to include().

Translations

The process to translate text in Python and JavaScript code is very similar. You could have noticed these lines at the beginning of the petstore.js file:

These lines are simply used to import the translation functions in the current JavaScript module. They are used thus:

In Odoo, translations files are automatically generated by scanning the source code. All piece of code that calls a certain function are detected and their content is added to a translation file that will then be sent to the translators. In Python, the function is _(). In JavaScript the function is _t() (and also _lt()).

_t() will return the translation defined for the text it is given. If no translation is defined for that text, it will return the original text as-is.

_lt() (“lazy translate”) is similar but somewhat more complex: instead of translating its parameter immediately, it returns an object which, when converted to a string, will perform the translation.

It is used to define translatable terms before the translations system is initialized, for class attributes for instance (as modules are loaded before the user’s language is configured and translations are downloaded).

Communication with the Odoo Server

Contacting Models

Most operations with Odoo involve communicating with models implementing business concern, these models will then (potentially) interact with some storage engine (usually PostgreSQL).

Although jQuery provides a $.ajax function for network interactions, communicating with Odoo requires additional metadata whose setup before every call would be verbose and error-prone. As a result, Odoo web provides higher-level communication primitives.

To demonstrate this, the file petstore.py already contains a small model with a sample method:

This declares a model with two fields, and a method my_method() which returns a literal dictionary.

Here is a sample widget that calls my_method() and displays the result:

The class used to call Odoo models is odoo.Model(). It is instantiated with the Odoo model’s name as first parameter (oepetstore.message_of_the_day here).

call() can be used to call any (public) method of an Odoo model. It takes the following positional arguments:

name
The name of the method to call, my_method here
args
an array of positional arguments to provide to the method. Because the example has no positional argument to provide, the args parameter is not provided.

Here is an other example with positional arguments:

kwargs
a mapping of keyword arguments to pass. The example provides a single named argument context.

call() returns a deferred resolved with the value returned by the model’s method as first argument.

CompoundContext

The previous section used a context argument which was not explained in the method call:

The context is like a “magic” argument that the web client will always give to the server when calling a method. The context is a dictionary containing multiple keys. One of the most important key is the language of the user, used by the server to translate all the messages of the application. Another one is the time zone of the user, used to compute correctly dates and times if Odoo is used by people in different countries.

The argument is necessary in all methods, otherwise bad things could happen (such as the application not being translated correctly). That’s why, when you call a model’s method, you should always provide that argument. The solution to achieve that is to use odoo.web.CompoundContext().

CompoundContext() is a class used to pass the user’s context (with language, time zone, etc…) to the server as well as adding new keys to the context (some models’ methods use arbitrary keys added to the context). It is created by giving to its constructor any number of dictionaries or other CompoundContext() instances. It will merge all those contexts before sending them to the server.

You can see the dictionary in the argument context contains some keys that are related to the configuration of the current user in Odoo plus the new_key key that was added when instantiating CompoundContext().

Queries

While call() is sufficient for any interaction with Odoo models, Odoo Web provides a helper for simpler and clearer querying of models (fetching of records based on various conditions): query() which acts as a shortcut for the common combination of search() and :read(). It provides a clearer syntax to search and read models:

versus:

  • query() takes an optional list of fields as parameter (if no field is provided, all fields of the model are fetched). It returns a odoo.web.Query() which can be further customized before being executed
  • Query() represents the query being built. It is immutable, methods to customize the query actually return a modified copy, so it’s possible to use the original and the new version side-by-side. See Query() for its customization options.

When the query is set up as desired, simply call all() to execute it and return a deferred to its result. The result is the same as read()’s, an array of dictionaries where each dictionary is a requested record, with each requested field a dictionary key.

Exercises

Existing web components

The Action Manager

In Odoo, many operations start from an action: opening a menu item (to a view), printing a report, …

Actions are pieces of data describing how a client should react to the activation of a piece of content. Actions can be stored (and read through a model) or they can be generated on-the fly (locally to the client by javascript code, or remotely by a method of a model).

In Odoo Web, the component responsible for handling and reacting to these actions is the Action Manager.

Using the Action Manager

The action manager can be invoked explicitly from javascript code by creating a dictionary describing an action of the right type, and calling an action manager instance with it.

do_action() is a shortcut of Widget() looking up the “current” action manager and executing the action:

The most common action type is ir.actions.act_window which provides views to a model (displays a model in various manners), its most common attributes are:

res_model
The model to display in views
res_id (optional)
For form views, a preselected record in res_model
views
Lists the views available through the action. A list of [view_id, view_type], view_id can either be the database identifier of a view of the right type, or false to use the view by default for the specified type. View types can not be present multiple times. The action will open the first view of the list by default.
target
Either current (the default) which replaces the “content” section of the web client by the action, or new to open the action in a dialog box.
context
Additional context data to use within the action.

Client Actions

Throughout this guide, we used a simple HomePage widget which the web client automatically starts when we select the right menu item. But how did the Odoo web know to start this widget? Because the widget is registered as a client action.

A client action is (as its name implies) an action type defined almost entirely in the client, in javascript for Odoo web. The server simply sends an action tag (an arbitrary name), and optionally adds a few parameters, but beyond that everything is handled by custom client code.

Our widget is registered as the handler for the client action through this:

instance.web.client_actions is a Registry() in which the action manager looks up client action handlers when it needs to execute one. The first parameter of add() is the name (tag) of the client action, and the second parameter is the path to the widget from the Odoo web client root.

When a client action must be executed, the action manager looks up its tag in the registry, walks the specified path and displays the widget it finds at the end.

On the server side, we had simply defined an ir.actions.client action:

and a menu opening the action:

Architecture of the Views

Much of Odoo web’s usefulness (and complexity) resides in views. Each view type is a way of displaying a model in the client.

The View Manager

When an ActionManager instance receive an action of type ir.actions.act_window, it delegates the synchronization and handling of the views themselves to a view manager, which will then set up one or multiple views depending on the original action’s requirements:

The Views

Most Odoo views are implemented through a subclass of odoo.web.View() which provides a bit of generic basic structure for handling events and displaying model information.

The search view is considered a view type by the main Odoo framework, but handled separately by the web client (as it’s a more permanent fixture and can interact with other views, which regular views don’t do).

A view is responsible for loading its own description XML (using fields_view_get) and any other data source it needs. To that purpose, views are provided with an optional view identifier set as the view_id attribute.

Views are also provided with a DataSet() instance which holds most necessary model information (the model name and possibly various record ids).

Views may also want to handle search queries by overriding do_search(), and updating their DataSet() as necessary.

The Form View Fields

A common need is the extension of the web form view to add new ways of displaying fields.

All built-in fields have a default display implementation, a new form widget may be necessary to correctly interact with a new field type (e.g. a GIS field) or to provide new representations and ways to interact with existing field types (e.g. validate Char fields which should contain email addresses and display them as email links).

To explicitly specify which form widget should be used to display a field, simply use the widget attribute in the view’s XML description:

Fields are instantiated by the form view after it has read its XML description and constructed the corresponding HTML representing that description. After that, the form view will communicate with the field objects using some methods. These methods are defined by the FieldInterface interface. Almost all fields inherit the AbstractField abstract class. That class defines some default mechanisms that need to be implemented by most fields.

Here are some of the responsibilities of a field class:

  • The field class must display and allow the user to edit the value of the field.
  • It must correctly implement the 3 field attributes available in all fields of Odoo. The AbstractField class already implements an algorithm that dynamically calculates the value of these attributes (they can change at any moment because their value change according to the value of other fields). Their values are stored in Widget Properties (the widget properties were explained earlier in this guide). It is the responsibility of each field class to check these widget properties and dynamically adapt depending of their values. Here is a description of each of these attributes:
    • required: The field must have a value before saving. If required is true and the field doesn’t have a value, the method is_valid() of the field must return false.
    • invisible: When this is true, the field must be invisible. The AbstractField class already has a basic implementation of this behavior that fits most fields.
    • readonly: When true, the field must not be editable by the user. Most fields in Odoo have a completely different behavior depending on the value of readonly. As example, the FieldChar displays an HTML <input> when it is editable and simply displays the text when it is read-only. This also means it has much more code it would need to implement only one behavior, but this is necessary to ensure a good user experience.
  • Fields have two methods, set_value() and get_value(), which are called by the form view to give it the value to display and get back the new value entered by the user. These methods must be able to handle the value as given by the Odoo server when a read() is performed on a model and give back a valid value for a write(). Remember that the JavaScript/Python data types used to represent the values given by read() and given to write() is not necessarily the same in Odoo. As example, when you read a many2one, it is always a tuple whose first value is the id of the pointed record and the second one is the name get (ie: (15, "Agrolait")). But when you write a many2one it must be a single integer, not a tuple anymore. AbstractField has a default implementation of these methods that works well for simple data type and set a widget property named value.

Please note that, to better understand how to implement fields, you are strongly encouraged to look at the definition of the FieldInterface interface and the AbstractField class directly in the code of the Odoo web client.

Creating a New Type of Field

In this part we will explain how to create a new type of field. The example here will be to re-implement the FieldChar class and progressively explain each part.

Simple Read-Only Field

Here is a first implementation that will only display text. The user will not be able to modify the content of the field.

In this example, we declare a class named FieldChar2 inheriting from AbstractField. We also register this class in the registry instance.web.form.widgets under the key char2. That will allow us to use this new field in any form view by specifying widget="char2" in the <field/> tag in the XML declaration of the view.

In this example, we define a single method: render_value(). All it does is display the widget property value. Those are two tools defined by the AbstractField class. As explained before, the form view will call the method set_value() of the field to set the value to display. This method already has a default implementation in AbstractField which simply sets the widget property value. AbstractField also watch the change:value event on itself and calls the render_value() when it occurs. So, render_value() is a convenience method to implement in child classes to perform some operation each time the value of the field changes.

In the init() method, we also define the default value of the field if none is specified by the form view (here we assume the default value of a char field should be an empty string).

Read-Write Field

Read-only fields, which only display content and don’t allow the user to modify it can be useful, but most fields in Odoo also allow editing. This makes the field classes more complicated, mostly because fields are supposed to handle both editable and non-editable mode, those modes are often completely different (for design and usability purpose) and the fields must be able to switch between modes at any moment.

To know in which mode the current field should be, the AbstractField class sets a widget property named effective_readonly. The field should watch for changes in that widget property and display the correct mode accordingly. Example:

In the start() method (which is called immediately after a widget has been appended to the DOM), we bind on the event change:effective_readonly. That allows us to redisplay the field each time the widget property effective_readonly changes. This event handler will call display_field(), which is also called directly in start(). This display_field() was created specifically for this field, it’s not a method defined in AbstractField or any other class. We can use this method to display the content of the field depending on the current mode.

From now on the conception of this field is typical, except there is a lot of verifications to know the state of the effective_readonly property:

  • In the QWeb template used to display the content of the widget, it displays an <input type="text" /> if we are in read-write mode and nothing in particular in read-only mode.
  • In the display_field() method, we have to bind on the change event of the <input type="text" /> to know when the user has changed the value. When it happens, we call the internal_set_value() method with the new value of the field. This is a convenience method provided by the AbstractField class. That method will set a new value in the value property but will not trigger a call to render_value() (which is not necessary since the <input type="text" /> already contains the correct value).
  • In render_value(), we use a completely different code to display the value of the field depending if we are in read-only or in read-write mode.

The Form View Custom Widgets

Form fields are used to edit a single field, and are intrinsically linked to a field. Because this may be limiting, it is also possible to create form widgets which are not so restricted and have less ties to a specific lifecycle.

Custom form widgets can be added to a form view through the widget tag:

This type of widget will simply be created by the form view during the creation of the HTML according to the XML definition. They have properties in common with the fields (like the effective_readonly property) but they are not assigned a precise field. And so they don’t have methods like get_value() and set_value(). They must inherit from the FormWidget abstract class.

Form widgets can interact with form fields by listening for their changes and fetching or altering their values. They can access form fields through their field_manager attribute:

FormWidget is generally the FormView() itself, but features used from it should be limited to those defined by FieldManagerMixin(), the most useful being:

  • get_field_value(field_name)() which returns the value of a field.
  • set_values(values)() sets multiple field values, takes a mapping of {field_name: value_to_set}
  • An event field_changed:field_name is triggered any time the value of the field called field_name is changed
[1] as a separate concept from instances. In many languages classes are full-fledged objects and themselves instance (of metaclasses) but there remains two fairly separate hierarchies between classes and instances
[2] as well as papering over cross-browser differences, although this has become less necessary over time
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