168 lines
6.7 KiB
Markdown
168 lines
6.7 KiB
Markdown
@title
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Dynamic Forms
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@intro
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Render dynamic forms with FormGroup
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@description
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We can't always justify the cost and time to build handcrafted forms,
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especially if we'll need a great number of them, they're similar to each other, and they change frequently
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to meet rapidly changing business and regulatory requirements.
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It may be more economical to create the forms dynamically, based on metadata that describe the business object model.
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In this cookbook we show how to use `formGroup` to dynamically render a simple form with different control types and validation.
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It's a primitive start.
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It might evolve to support a much richer variety of questions, more graceful rendering, and superior user experience.
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All such greatness has humble beginnings.
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In our example we use a dynamic form to build an online application experience for heroes seeking employment.
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The agency is constantly tinkering with the application process.
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We can create the forms on the fly *without changing our application code*.
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<a id="toc"></a>## Table of contents
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[Bootstrap](#bootstrap)
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[Question Model](#object-model)
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[Form Component](#form-component)
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[Questionnaire Metadata](#questionnaire-metadata)
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[Dynamic Template](#dynamic-template)
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**See the <live-example name="cb-dynamic-form"></live-example>**.
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<a id="bootstrap"></a>## Bootstrap
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We start by creating an `NgModule` called `AppModule`.
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In our example we will be using Reactive Forms.
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Reactive Forms belongs to a different `NgModule` called `ReactiveFormsModule`, so in order to access any Reactive Forms directives, we have to import `ReactiveFormsModule` from the `@angular/forms` library.
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We bootstrap our `AppModule` in main.ts.
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<md-tab-group>
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<md-tab label="app.module.ts">
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{@example 'cb-dynamic-form/ts/src/app/app.module.ts'}
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</md-tab>
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<md-tab label="main.ts">
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{@example 'cb-dynamic-form/ts/src/main.ts'}
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</md-tab>
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</md-tab-group>
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<a id="object-model"></a>## Question Model
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The next step is to define an object model that can describe all scenarios needed by the form functionality.
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The hero application process involves a form with a lot of questions.
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The "question" is the most fundamental object in the model.
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We have created `QuestionBase` as the most fundamental question class.
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{@example 'cb-dynamic-form/ts/src/app/question-base.ts'}
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From this base we derived two new classes in `TextboxQuestion` and `DropdownQuestion` that represent Textbox and Dropdown questions.
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The idea is that the form will be bound to specific question types and render the appropriate controls dynamically.
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`TextboxQuestion` supports multiple html5 types like text, email, url etc via the `type` property.
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{@example 'cb-dynamic-form/ts/src/app/question-textbox.ts'}
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`DropdownQuestion` presents a list of choices in a select box.
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{@example 'cb-dynamic-form/ts/src/app/question-dropdown.ts'}
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Next we have defined `QuestionControlService`, a simple service for transforming our questions to a `FormGroup`.
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In a nutshell, the form group consumes the metadata from the question model and allows us to specify default values and validation rules.
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{@example 'cb-dynamic-form/ts/src/app/question-control.service.ts'}
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<a id="form-component"></a>## Question form components
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Now that we have defined the complete model we are ready to create components to represent the dynamic form.
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`DynamicFormComponent` is the entry point and the main container for the form.
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<md-tab-group>
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<md-tab label="dynamic-form.component.html">
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{@example 'cb-dynamic-form/ts/src/app/dynamic-form.component.html'}
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</md-tab>
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<md-tab label="dynamic-form.component.ts">
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{@example 'cb-dynamic-form/ts/src/app/dynamic-form.component.ts'}
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</md-tab>
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</md-tab-group>
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It presents a list of questions, each question bound to a `<df-question>` component element.
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The `<df-question>` tag matches the `DynamicFormQuestionComponent`,
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the component responsible for rendering the details of each _individual_ question based on values in the data-bound question object.
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<md-tab-group>
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<md-tab label="dynamic-form-question.component.html">
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{@example 'cb-dynamic-form/ts/src/app/dynamic-form-question.component.html'}
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</md-tab>
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<md-tab label="dynamic-form-question.component.ts">
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{@example 'cb-dynamic-form/ts/src/app/dynamic-form-question.component.ts'}
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</md-tab>
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</md-tab-group>
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Notice this component can present any type of question in our model.
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We only have two types of questions at this point but we can imagine many more.
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The `ngSwitch` determines which type of question to display.
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In both components we're relying on Angular's **formGroup** to connect the template HTML to the
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underlying control objects, populated from the question model with display and validation rules.
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`formControlName` and `formGroup` are directives defined in `ReactiveFormsModule`. Our templates can can access these directives directly since we imported `ReactiveFormsModule` from `AppModule`.
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<a id="questionnaire-metadata"></a>## Questionnaire data`DynamicFormComponent` expects the list of questions in the form of an array bound to `@Input() questions`.
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The set of questions we have defined for the job application is returned from the `QuestionService`.
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In a real app we'd retrieve these questions from storage.
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The key point is that we control the hero job application questions entirely through the objects returned from `QuestionService`.
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Questionnaire maintenance is a simple matter of adding, updating, and removing objects from the `questions` array.
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{@example 'cb-dynamic-form/ts/src/app/question.service.ts'}
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Finally, we display an instance of the form in the `AppComponent` shell.
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{@example 'cb-dynamic-form/ts/src/app/app.component.ts'}
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<a id="dynamic-template"></a>## Dynamic Template
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Although in this example we're modelling a job application for heroes, there are no references to any specific hero question
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outside the objects returned by `QuestionService`.
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This is very important since it allows us to repurpose the components for any type of survey
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as long as it's compatible with our *question* object model.
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The key is the dynamic data binding of metadata used to render the form
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without making any hardcoded assumptions about specific questions.
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In addition to control metadata, we are also adding validation dynamically.
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The *Save* button is disabled until the form is in a valid state.
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When the form is valid, we can click *Save* and the app renders the current form values as JSON.
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This proves that any user input is bound back to the data model.
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Saving and retrieving the data is an exercise for another time.
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The final form looks like this:
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<figure class='image-display'>
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<img src="assets/images/cookbooks/dynamic-form/dynamic-form.png" alt="Dynamic-Form"> </img>
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</figure>
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[Back to top](#top) |