angular-cn/public/docs/ts/latest/guide/forms.jade

include ../../../../_includes/_util-fns

<!-- http://plnkr.co/edit/wg154K -->
:marked
  We’ve all used a form to login, submit a help request, place an order, book a flight,
  schedule a meeting and perform countless other data entry tasks.
  Forms are the mainstay of business applications.

  Any seasoned web developer can slap together an HTML form with all the right tags.
  It's more challenging to create a cohesive data entry experience that guides the
  user efficiently and effectively through the workflow behind the form.

  *That* takes design skills that are, to be frank, well out of scope for this chapter.

  It also takes framework support for
  **two-way data binding, change tracking, validation, and error handling**
  ... which we shall cover in this chapter on Angular forms.

  We will build a simple form from scratch, one step at a time. Along the way we'll learn

  - how to build an Angular form with a component and template

  - the `ng-model` two-way data binding syntax for reading and writing values to input controls

  - the `ng-control` directive to track the change state and validity of form controls

  - the special CSS classes that `ng-control` adds to form controls and how we can use them to provide strong visual feedback

  - how to display validation errors to users and enable/disable form controls

  - how to share information across controls with template local variables

.l-main-section
:marked
  ## Template-Driven Forms

  Many of us will build forms by writing templates in the Angular [template syntax](./template-syntax.html) with
  the form-specific Directives and techniques described in this chapter.
.l-sub-section
  :marked
    That's not the only way to create a form but it's the way we'll cover in this chapter.
:marked
  We can build almost any form we need with an Angular template ... login forms, contact forms ... pretty much any business forms.
  We can lay out the controls creatively, bind them to data, specify validation rules and display validation errors,
  conditionally enable or disable specific controls, trigger built-in visual feedback, and much more.

  It will be pretty easy because Angular handles many of the repeative, boiler plate tasks we'd
  otherwise wrestle with ourselves.

  We'll discuss and learn to build the following template-driven form:

figure.image-display
  img(src="/resources/images/devguide/forms/hf-1.png" alt="Clean Form")

:marked
  Here at the *Hero Employment Agency* we use this form to maintain personal information about the
  heroes in our stable. Every hero needs a job. It's our company mission to match the right hero with the right crisis!

  Two of the three fields on this form are required. Required fields have a green bar on the left to make them easy to spot.

  If we delete the hero name, the form displays a validation error in an attention grabbing style:

figure.image-display
  img(src="/resources/images/devguide/forms/hf-2.png" alt="Invalid, Name Required")

:marked
  Note that the submit button is disabled and the "required" bar to the left of the input control changed from green to red.

.l-sub-section
  p We'll' customize the colors and location of the "required" bar with standard CSS.

:marked
  We will build this form in the following sequence of small steps

  1. Create the `Hero` model class
  1. Create the component that controls the form
  1. Create a template with the initial form layout
  1. Add the **ng-model** directive to each form input control
  1. Add the **ng-control** directive to each form input control
  1. Add custom CSS to provide visual feedback
  1. Show and hide validation error messages
  1. Handle form submission with **ng-submit**
  1. Disable the form’s submit button until the form is valid

:marked
  ## Setup
  Create a new project folder (`angular2-forms`) and follow the steps in the [QuickStart](../quickstart.html).

  ## Create the Hero Model Class

  As users enter form data, we capture their changes and update an instance of a model.
  We can't layout the form until we know what the model looks like.

  A model can be as simple as a "property bag" that holds facts about a thing of application importance.
  That describes well our `Hero` class with its three required fields (`id`, `name`, `power`)
  and one optional field (`alterEgo`).

  Create a new file called `hero.ts` and give it the following class definition:

+makeExample('forms/ts/src/app/hero.ts')

:marked
  It's an anemic model with few requirements and no behavior. Perfect for our demo.

  The TypeScript compiler generates a public field for each `public` constructor parameter and
  assigns the parameter’s value to that field automatically when we create new heroes like this:
  ```
  let myHero = new Hero(42, 'SkyDog', 'Fetch any object at any distance', 'Leslie Rollover');
  console.log('My hero is called ' + myHero.name); // "My hero is called SkyDog"
  ```
  The `alterEgo` is optional and the constructor lets us omit it; note the (?) in `alterEgo?`.

.l-main-section
:marked
  ## Create a Form component

  An Angular form has two parts: an HTML-based template and a code-based Component to handle data and user interactions.

  We begin with the Component because it states, in brief, what the Hero editor can do.

  Create a new file called `hero-form.component.ts` and give it the following definition:

+makeExample('forms/ts/src/app/hero-form.component.ts', 'first')

:marked
  There’s nothing special about this component, nothing to distinguish it from any component we've written before,
  nothing form-specific about it ... except, perhaps, the tell-tale `FORM_DIRECTIVES` import.

  Understanding this component requires only the Angular 2 concepts we’ve learned in previous chapters

  1. We import a standard set of symbols from the Angular library.
  We don't have a template yet but we usually import `CORE_DIRECTIVES` and it doesn't surprise us to
  import something called `FORM_DIRECTIVES`, given that we'll be writing a form

  1. The `@Component` selector value of "hero-form" means we can drop this form in a parent template with a `<hero-form>` tag.

  1. The `templateUrl` property points to a separate file for template HTML called `hero-form.component.html`.

  1. We defined dummy data for `model` and `powers` as befits a demo.
  Down the road, we can inject a data service to get and save real data
  or perhaps expose these properties as [inputs and outputs](./template-syntax.html#inputs-outputs) for binding to a
  parent component. None of this concerns us now and these future changes won't affect our form.

  1. We threw in a `diagnostic` property at the end to return a JSON representation of our model.
  It'll help us see what we're doing during our development; we've left ourselves a cleanup note to discard it later.

  We may wonder why we aren't writing the template inline in the component file as we have often done
  elsewhere in the Developer Guide.

  There is no “right” answer for all occasions. We kind of like inline templates when they are short.
  Most form templates won't be short. TypeScript and JavaScript files generally aren't the best place to
  write (or read) large stretches of HTML and few editors are much help with files that have a mix of HTML and code.
  We also like short files with a clear and obvious purpose like this one.

  We made a good choice to put the HTML template elsewhere. Let's write it.

.l-main-section
:marked
  ## Revise the *app.ts*

  `app.ts` is the application's root component. It will host our new `HeroFormComponent`.

  Replace the contents of the "QuickStart" version with the following:
+makeExample('forms/ts/src/app/app.ts')

:marked
.l-sub-section
  :marked
    There are only three changes:

    1. We import the new `HeroFormComponent`.

    1. The `template` is simply the new element tag identified by the component's `select` property.

    1. The `directives` array tells Angular that our templated depends upon the `HeroFormComponent`
    which is itself a Directive (as are all Components).

.l-main-section
:marked
  ## Create an initial HTML Form Template

  Create a new template file called `hero-form.component.html` and give it the following definition:

+makeExample('forms/ts/src/app/hero-form.component.html', 'start')

:marked
  That is plain old HTML 5. We're presenting two of the `Hero` fields, `name` and `alterEgo`, and
  opening them up for user input in input boxes.

  The "Name" `<input>` control has the HTML5 `required` attribute;
  the "Alter Ego" `<input>` control does not because `alterEgo` is optional.

  We've got a "Submit" button at the bottom with some classes on it.

  **We are not using Angular yet**. There are no bindings. No extra directives. Just layout.

  The `container`,`form-group`, `form-control`, and `btn` classes are CSS Bootstrap. Purely cosmetic.
  We're using Bootstrap to gussy up our form.
  Hey, what's a form without a little style!

.l-sub-section
  :marked
    Since we're using [CSS Boostrap](http://getbootstrap.com/css/).
    now might be a good time to install it into our project.
    We can do that with npm.

    Open a terminal window and enter the command:
  code-example(language="html" escape="html").
    npm install bootstrap
  :marked
    <br>Open the `index.html` and add the following line wherever we like to put our CSS
  +makeExample('forms/ts/src/index.html', 'bootstrap')(format=".")

.callout.is-important
  header Angular Forms Does Not Require A Style Library
  :marked
    Angular makes no use of the `container`, `form-group`, `form-control`, and `btn` classes or
    the styles of any external library. We are welcome to use the CSS library we choose
    ... or none at all.

.l-main-section
:marked
  ## Add Powers with ***ng-for**
  Our hero may choose one super power from a fixed list of Agency-approved powers.
  We maintain that list internally (in `HeroFormComponent`).

  We'll add a `select` to our
  form and bind the options to the `powers` list using `NgFor`,
  a technique we might have seen before in the ["Displaying Data"](./displaying-data.html) chapter.

  Add the following HTML *immediately below* the "Alter Ego" group.
+makeExample('forms/ts/src/app/hero-form.component.html', 'powers')

:marked
  We are repeating the `<options>` tag for each power in the list of Powers.
  The `#p` local template variable is a different power in each iteration;
  we display its name using the interpolation syntax with the double-curly-braces.

.l-main-section
:marked
  ## Two-way data binding with ***ng-model**
  We might be disappointed if we ran the app right now.

figure.image-display
  img(src="/resources/images/devguide/forms/hf-3.png" alt="Early form with no binding")
:marked
  We quickly realize that we are not binding to the `Hero` yet.
  We know how to do that from earlier chapters.
  We learned show data on screen with a Property Binding in "[Displaying Data](./displaying-data.html)".
  We learned to listen for DOM events with an
  Event Binding and how to extract values from the screen
  in "[User Input](./user-input.html)".

  Now we need to display, listen, and extract at the same time.

  We could use those techniques again in our form.
  Instead we'll introduce something new, the `NgModel` directive, that
  makes binding our form to the model super-easy.

  Find the `<input>` tag for the "Name" and update it like this

+makeExample('forms/ts/src/app/hero-form.component.html', 'ng-model-1')

.l-sub-section
  :marked
    We appended a diagnostic interpolation after the input tag
    so we can see what we're doing.
    We left ourselves a note to throw it way when we're done.

:marked
  Focus on the binding syntax: `[(ng-model)]="..."`.

  If we ran the app right now and started typing in the "Name" input box,
  adding and deleting characters, we'd see them appearing and disappearing
  from the interpolated text.
  At some point it might look like this.
figure.image-display
  img(src="/resources/images/devguide/forms/ng-model-in-action.png" alt="ng-model in action")
:marked
  The diagnostic is evidence that we really are flowing values from the input box to the model and
  back again. **That's two-way data binding!**

  Let's add similar `[(ng-model)]` bindings to "Alter Ego" and "Hero Power".
  We'll ditch the input box binding message
  and add a new binding at the top to the component's `diagnostic` property.
  Then we can confirm that we are in fact two-way data binding *to the entire Hero model*.

  After revision the core of our form should have three `[(ng-model)]` bindings that
  look much like this:

+makeExample('forms/ts/src/app/hero-form.component.html', 'ng-model-2')

:marked
  If we ran the app right now and made a bunch of changes at some point it might look like this.
figure.image-display
  img(src="/resources/images/devguide/forms/ng-model-in-action-2.png" alt="ng-model in super action")
:marked
  We've changed every Hero model property and the diagnostic near the top of the form
  confirms that our changes are reflected in the model.

  ** We're done with the diagnostic binding. Delete it now.**

.alert.is-helpful
  :marked
    Although `NgModel` is officially a "Forms" directive we can use `[(ng-model)]` and two-way binding outside of forms too.
:marked
  ## Inside [(ng-model)]
  Do we *really want* to know? If we're just happy that it works, move on to the next topic in this chapter.

  Otherwise, stick around for this note.

.l-sub-section
  :marked
    The punctuation in the binding syntax, <span style="font-family:courier"><b>[()]</b></span>, is a good clue to what's going on.

    We write a Property Binding to flow data from the model to a target property on screen.
    We identify that target property by surrounding its name in brackets, <span style="font-family:courier"><b>[]</b></span>.
    This is a one-way data binding **from the model to the view**.

    We write an Event Binding to flow data from the target property on screen to the model.
    We identify that target property by surrounding its name in parentheses, <span style="font-family:courier"><b>()</b></span>.
    This is a one-way data binding in the opposite direction **from the view to the model**.

    No wonder Angular chose to combine the punctuation as <span style="font-family:courier"><b>[()]</b></span>
    to signify a two-way data binding and a **flow of data in both directions**.

    In fact, we can break the `NgModel` binding into its two separate modes
    as we do in this re-write of the "Name" `<input>` binding:
  +makeExample('forms/ts/src/app/hero-form.component.html', 'ng-model-3')

  :marked
    <br>The Property Binding should feel familiar. The Event Binding might seem strange.

    The name `ng-model-change` is not an event we recognize.
    It is a real event property ... of the `NgModel` directive.
    When Angular sees a binding target in the form <span style="font-family:courier">[(abc)]</span>,
    it expects the `abc` directive to have an `abc` input property and an `abc-change` output property.

    The other oddity is the template expression, `model.name = $event`.
    We're used to seeing an `$event` object coming from a DOM event.
    The `ng-model-change` property doesn't produce a DOM event; it's an Angular `EventEmitter`
    property that returns the input box value when it fires ... which is precisely what
    we should assign to the model's `name' property.

    Nice to know but is it practical? We'd always prefer the `[(ng-model)]`.
    We might split the binding if we had to do something special in
    the event handling such as debounce or throttle the key strokes.

    Learn more about `NgModel` and other template syntax in the
    [Template Syntax](./template-syntax.html) chapter.

.l-main-section
:marked
  ## Track change-state and validity with **ng-control**

  A form isn't just about data binding. We'd also like to know the state of the controls on our form.
  The `NgControl` directive keeps track of control state for us.

.callout.is-helpful
  header NgControl requires Form
  :marked
    The `NgControl` is one of a family of `NgForm` directives that can only be applied to
    a control within a `<form`> tag.
:marked
  Our application can ask an `NgControl` instance if
  * the user touched the control (`ng-touched` | `ng-untouched`)
  * the value changed (`ng-pristine` | `ng-dirty`)
  * is the value is valid (`ng-valid` | `ng-invalid`)

  `NgControl` doesn't just track state; it updates the control with special
  Angular CSS classes from the set we listed above.
  We can leverage those class names to change the appearance of the
  control and make messages appear or disappear.

  We'll explore those effects soon. Right now
  we should **add `ng-control`to all three of our form controls**,
  starting with the "Name" input box
+makeExample('forms/ts/src/app/hero-form.component.html', 'ng-control-1')
:marked
  Be sure to assign a unique name to each `ng-control` directive.

.l-sub-section
  :marked
    Angular registers controls under their `ng-control` names
    with the `NgForm`.
    We didn't add the `NgForm` directive explicitly but it's here
    and we'll talk it [later in this chapter](#ng-form).

.l-main-section
:marked
  ## Add Custom CSS for Visual Feedback

  `NgControl` doesn't just track state. It updates the control with three classes, one
  each from the following pairs of Angular form CSS classes.
  * control visited: (`ng-touched` | `ng-untouched`)
  * value changed: (`ng-pristine` | `ng-dirty`)
  * validity: (`ng-valid` | `ng-invalid`)

  Let's add a temporary [local template variable](./template-syntax.html#local-vars) named **spy**
  to the "Name" `<input>` tag and use the spy to display those classes with an interpolation binding.

+makeExample('forms/ts/src/app/hero-form.component.html', 'ng-control-2')

:marked
  If we ran the app, focused our attention on the "Name" input box, and followed the next four steps *precisely*

  1. Look but don't touched
  1. Click in the input box, then click outside the text input box
  1. Add slashes to the end of the name
  1. Erase the name

  ... we would see the following four sets of class names and their transitions:
figure.image-display
  img(src="/resources/images/devguide/forms/ng-control-class-changes.png" alt="Invalid Form")

:marked
  The (`ng-valid` | `ng-invalid`) pair are most interesting to us. We want to send a
  strong visual signal when the data are invalid and we want to mark required fields.

  We realize we can do both at the same time with a colored bar on the left of the input box:

figure.image-display
  img(src="/resources/images/devguide/forms/validity-required-indicator.png" alt="Invalid Form")

:marked
  We achieve this effect by adding two styles to a new `styles.css` file
  that we add to our project as a sibling to `index.html`.

+makeExample('forms/ts/src/styles.css')
:marked
  These styles select for the two Angular validity classes and the HTML 5 "required" attribute.

  We update the `<head>` of the `index.html` to include this style sheet.
+makeExample('forms/ts/src/index.html', 'styles')(format=".")
:marked
  ## Show and Hide Validation Error messages

  We can do better.

  The "Name" input box is required. Clearing it turns the bar red. That says *something* is wrong but we
  don't know *what* is wrong or what to do about it.
  We can leverage the `ng-invalid` class to reveal a helpful message.

  Here's the way it should look when the user deletes the name:
figure.image-display
  img(src="/resources/images/devguide/forms/name-required-error.png" alt="Name required")

:marked
  To achieve this effect we extend the `<input>` tag with
  1. a [local template variable](./template-syntax.html#local-vars)
  1. the "*is required*" message in a nearby `<div>` which we'll display only if the control is invalid.

  Here's how we do it for the "name" input box:
+makeExample('forms/ts/src/app/hero-form.component.html', 'name-with-error-msg')
:marked
  We initialized the template local variable with the word "form" (`#name="form"`)

  Angular recognizes that syntax and sets the `name` variable
  to the `Control` object identified by the `ng-control` directive which,
  not coincidentally, we called "name".

  We bind the `Control` object's `valid` property to the element's `hidden` property.
  While the control is valid, the message is hidden;
  if it becomes invalid, the message is revealed.
<a id="ng-form"></a>
.l-sub-section
  :marked
    Recall from the previous section that `ng-control` registered this input box with the
    `NgForm` directive as "name".

    We didn't add the **[`NgForm`](../api/core/NgForm-class.html) directive** explicitly.
    Angular added it surreptiously, wrapping it around the `<form>` element when we
    told the `HeroFormComponent` to use the `FORM_DIRECTIVES` like this

  +makeExample('forms/ts/src/app/hero-form.component.ts', 'directives')
  <br>
  :marked
    The `NgForm` directive  supplements the `form` element with additional features.
    It collects `Controls` (elements identified by an `ng-control` directive)
    and monitors their properties including their validity.
    It has its own `valid` property which is true only if every contained
    control is valid.

    In this example, we are pulling the "name" control out of its `controls` collection
    and assigning it to the template local variable so that we can
    access the control's properties ... such as the control's own `valid` property.
:marked
  The "AlterEgo" is optional so we can leave that be.

  "Power" selection is required.
  We can add the same kind of error handling to the `<select>` if we  want
  but it's not imperative because the selection box already constrains the
  power to valid value.

.l-main-section
:marked
  ## Submit the form with **ng-submit**
  The user should be able to submit this form after filling it in.
  The "Submit" button at the bottom of the form
  does nothing on its own but it will
  trigger a form submit because of its type (`type="submit"`).

  A "form submit" is meaningless at the moment.
  We'll update the `<form>` tag with another Angular directive, `NgSubmit`,
  and bind it to our `HeroFormComponent.submit()` method with an EventBinding
+makeExample('forms/ts/src/app/hero-form.component.html', 'ng-submit')

:marked
  We slipped in something extra there at the end!  We defined a
  template local variable, **`#hf`**, and initialized it with the value, "form".

  The variable `hf` is now a handle to the `NgForm` as we [discussed earlier](#ng-form)
  with respect to `ng-control` although this time we have a reference to the form
  rather than a control.

  We'll bind the Form's over-all validity via
  the `hf` variable to the button's `disabled` property
  using an Event Binding. Here's the code:
+makeExample('forms/ts/src/app/hero-form.component.html', 'submit-button')
:marked
  If we run the application now, we find that the button is enabled.
  It doesn't do anything useful yet but it's alive.

  Now if we delete the "Name", we violate the "required" rule which
  is duely noted in our error message.

  Check the "Submit" button. It should be disabled.

  Not impressed?  Think about it for a moment. What would we have to do to
  wire the button's enable/disabled state to the form's validity without Angular's help?

  For us, it was as simple as
  1. Define a template local variable on the (enhanced) form element
  2. Reference that variable in a button some 50 lines away.

.l-main-section
:marked
  ## Toggle two form regions (Extra Credit)
  Submitting the form isn't terribly dramatic at the moment.
.l-sub-section
  :marked
    An unsurprising observation for a demo. To be honest,
    jazzing it up won't teach us anything new about forms.
    But this is an opportunity to exercise some of our newly won
    binding skills.
    If we're not interested, we can skip to the chapter's conclusion
    and not miss a thing.
:marked
  Let's do something more strikingly visual.
  Let's hide the data entry area and display something else.

  Start by wrapping the form in a `<div>` and binding
  its `hidden` property to the `HeroFormComponent.submitted` property.

+makeExample('forms/ts/src/app/hero-form.component.html', 'edit-div')

:marked
  The main form is visible from the start because the
  the `submitted` property is false until we submit the form
  ... as this fragment from the `HeroFormComponent` reminds us:

+makeExample('forms/ts/src/app/hero-form.component.ts', 'submitted')

:marked
  When we click the "Submit" button, the `submitted` flag becomes true and the form disappears
  as planned.

  Now we need to show something else while the form is in the submitted state.
  Add the following block of HTML below the `<div>` wrapper we just wrote:
+makeExample('forms/ts/src/app/hero-form.component.html', 'submitted')

:marked
  There's our hero again, displayed read-only with interpolation bindings.
  This slug of HTML only appears while the component is in the submitted state.

  There's an "Edit" button whose click event we bound to an expression
  that clears the `submitted` flag.

  Click it and this block disappears and the editable form reappears.

  That's as much drama as we can muster for now.

.l-main-section
:marked
  ## Conclusion

  The Angular 2 form discussed in this chapter takes advantage of the following framework features to provide support for data modification, validation and more:

  - An Angular HTML form template.
  - A form component class with a `Component` decorator.
  - The `ng-submit` directive for handling the form submission.
  - Template local variables such as `#hf`, `#name`, `#alter-ego` and `#power`.
  - The `ng-model` directive for two-way data binding.
  - The `ng-control` for validation and form element change tracking.
  - The local variable’s `valid` property on input controls to check if a control is valid and show/hide error messages.
  - Property Binding  to disable the submit button when the form is invalid.
  - Custom CSS classes that provide visual feedback to users about required invalid controls.

  Here’s the final version of the application includes all of these framework features:

+makeTabs(
  `forms/ts/src/app/hero-form.component.html,
   forms/ts/src/app/hero-form.component.ts,
   forms/ts/src/app/hero.ts,
   forms/ts/src/app/app.ts,
   forms/ts/src/index.html,
   forms/ts/src/styles.css`,
  'final, final,,,,',
  `hero-form.component.html,
   hero-form.component.ts,
   hero.ts,
   app.ts,
   index.html,
   styles.css`)
:marked
  Our final project folder structure should look like this:
  ```
  angular2-forms
  ├── node_modules
  ├── src
  │    ├── app
  │    |    ├── app.ts
  │    |    ├── hero.ts
  │    |    ├── hero-form.component.html
  │    |    └── hero-form.component.ts
  │    ├── index.html
  │    ├── styles.css
  │    └── tsconfig.json
  └── package.json
  ```