How can I usecreate dynamic template to compile dynamic Component with Angular 20

Angular’s dynamic component creation empowers developers to build adaptable and flexible user interfaces. If you’re looking into how can I use/create dynamic template to compile dynamic Component with Angular 2.0 (and beyond, as the core concepts remain relevant), you’ve come to the right place. This guide walks you through the process of dynamically generating Angular components using templates defined at runtime. This capability is crucial for scenarios where the structure and content of a component depend on data fetched from a server, user input, or other dynamic factors. Mastering dynamic component creation opens doors to building highly customizable and data-driven applications, allowing for a more responsive and engaging user experience. We’ll cover the essential steps, from defining the component and its template to compiling and rendering it within your application. Let’s dive in and explore the power of dynamic components in Angular!

Understanding Dynamic Component Creation in Angular

Dynamic component creation in Angular refers to the process of generating and rendering components at runtime, rather than being pre-defined during the application’s build process. This is achieved by using Angular’s ComponentFactoryResolver to create component factories from component types and then injecting those components into the view. The ViewContainerRef is then used to anchor the dynamically created component within the DOM. A crucial aspect of dynamic component creation is the ability to define the template for the component dynamically, allowing for highly flexible and adaptable UIs. This is where the “dynamic template” aspect comes into play, enabling you to construct the visual representation of the component on the fly based on data or user interactions.

Consider a scenario where you have a dashboard that displays different types of widgets based on user preferences. Each widget could be a dynamic component with a template tailored to the specific widget type. By dynamically creating these components, you can easily add, remove, or modify widgets without requiring a rebuild of the application. This dynamic behavior is invaluable for creating extensible and customizable applications. According to a report by Statista, customizable software solutions are expected to grow by 15% annually, highlighting the increasing demand for dynamic and adaptable applications. This underscores the importance of understanding and implementing dynamic component creation in Angular development.

Angular’s architecture facilitates this dynamism through its dependency injection system and component factories. By injecting the ComponentFactoryResolver, a component can request the factory for any other component type. This factory then creates an instance of the component, which can be inserted into the view using the ViewContainerRef. The data for the dynamic component can be passed in using input bindings, and the component’s output events can be subscribed to, enabling seamless communication between the dynamic component and its host. This powerful mechanism enables developers to build sophisticated and responsive applications that adapt to changing requirements.

Creating a Dynamic Template

The heart of dynamic component creation lies in the ability to define and manipulate templates at runtime. A dynamic template is essentially a string of HTML that defines the structure and content of a component. This template can be constructed from various sources, such as data fetched from a server, user input, or a combination of both. To use a dynamic template, you’ll typically need to compile it into a component using Angular’s @NgModule and Compiler. This process involves creating a module and component on the fly, injecting the template into the component, and then compiling the module.

Let’s outline the general steps involved in creating a dynamic template and using it to compile a dynamic component:

Define the Dynamic Template: Construct an HTML string representing the template. This string can include Angular bindings, directives, and components.
Create a Dynamic Component: Define a component class that will use the dynamic template. This component will typically have input properties to receive data and output properties to emit events.
Create a Dynamic Module: Define a module that declares and exports the dynamic component. This module is necessary for compiling the component.
Compile the Dynamic Module: Use Angular’s Compiler to compile the dynamic module. This will generate a ModuleFactory.
Create the Component Instance: Use the ModuleFactory to create a module instance and then use the ComponentFactoryResolver to create a component factory for the dynamic component.
Insert the Component into the View: Use the ViewContainerRef to insert the dynamic component into the DOM.

For example, imagine you have a system that needs to render different form fields based on a configuration file. The configuration file might specify the type of input field (text, number, select, etc.) and its associated properties (label, validation rules, etc.). You can use this configuration to dynamically generate the HTML template for each form field, creating a dynamic form that adapts to the configuration. The following list outlines key considerations when creating dynamic templates:

Security: Be cautious when using dynamic templates, especially if the template source is user-provided. Sanitize the template to prevent cross-site scripting (XSS) attacks.
Performance: Compiling components dynamically can be resource-intensive. Consider caching compiled components or optimizing the template generation process to improve performance.
Maintainability: Dynamic templates can make code harder to understand and maintain. Use clear naming conventions and comments to document the purpose and structure of the templates.

Compiling the Dynamic Component

Compiling the dynamic component involves transforming the dynamic template and component class into a fully functional Angular component that can be rendered in the view. This is achieved using Angular’s Compiler, which is responsible for parsing the template, resolving dependencies, and generating the necessary code to create the component. The compilation process typically involves creating a dynamic module that declares and exports the dynamic component, and then using the Compiler to compile this module. The compiled module will then produce a ModuleFactory, which can be used to create an instance of the module and subsequently the component.

Here’s a more detailed breakdown of the compilation process. First, you define a dynamic module using @NgModule. This module includes the dynamic component in its declarations and exports arrays. Next, you inject the Compiler into your component or service. Then, you use the compileModuleAndAllComponentsAsync method of the Compiler to compile the dynamic module. This method returns a promise that resolves with a ModuleWithComponentFactories object. From this object, you can extract the ComponentFactory for your dynamic component. This ComponentFactory is then used to create an instance of the component and insert it into the view using ViewContainerRef.

The Compiler is a powerful tool, but it also requires careful handling. It’s important to ensure that the dynamic module is properly configured and that all dependencies are correctly resolved. Errors during compilation can be difficult to debug, so it’s essential to have a good understanding of Angular’s module system and component lifecycle. As noted in the Angular documentation, proper module configuration is critical for successful dynamic compilation [Angular Dynamic Component Loading]. The ability to dynamically compile components allows for highly adaptable and extensible applications that can respond to changing requirements without requiring a full rebuild.

For optimal performance, consider caching compiled components. Compiling a component is a relatively expensive operation, so if you need to create the same component multiple times, it’s more efficient to compile it once and then reuse the compiled ComponentFactory. You can use a simple cache to store the compiled factories and retrieve them when needed. This can significantly improve the performance of your application, especially if you are creating many dynamic components.

Rendering the Dynamic Component

Once you have compiled the dynamic component, the final step is to render it within your application’s view. This involves using the ViewContainerRef to insert the component into the DOM. The ViewContainerRef represents a container where you can attach dynamic components. To render the component, you first create an instance of the component using the ComponentFactory obtained from the compilation process. Then, you use the createComponent method of the ViewContainerRef to insert the component into the view. This method returns a ComponentRef, which provides access to the component instance and its associated view.

The createComponent method also allows you to specify an optional injector for the dynamic component. This injector can be used to provide dependencies to the component that are not available in the current scope. This is useful if your dynamic component requires specific services or configuration values. When creating the component instance, you can also pass data to the component using input bindings. This allows you to configure the component based on data fetched from a server or user input. The following is a summary of steps to render dynamic components:

Get a reference to the ViewContainerRef.
Use the ComponentFactory to create a component instance.
Set input properties on the component instance.
Insert the component into the view using ViewContainerRef.createComponent.

Properly rendering dynamic components ensures that they integrate seamlessly with the rest of your application. This requires careful management of component lifecycles, data binding, and event handling. As explained in this article about dynamic components, understanding component lifecycles is crucial dynamic components. For instance, you may need to implement the ngOnChanges lifecycle hook to respond to changes in input properties, or the ngOnDestroy hook to clean up resources when the component is destroyed. By carefully managing these aspects, you can create dynamic components that are both flexible and robust.

FAQ About Dynamic Templates and Components

**What is the main benefit of using dynamic components in Angular?**: Dynamic components allow for creating flexible and adaptable user interfaces that can change at runtime based on data or user input, without requiring a rebuild of the application.
**How do I prevent security vulnerabilities when using dynamic templates?**: Always sanitize the dynamic template, especially if the template source is user-provided, to prevent cross-site scripting (XSS) attacks. Use Angular's built-in sanitization features or a trusted library to sanitize the HTML.
**What is `ViewContainerRef` used for?**: `ViewContainerRef` represents a container where you can attach dynamic components. It provides methods for creating, inserting, and removing components from the view.
**What is the role of `ComponentFactoryResolver`?**: The `ComponentFactoryResolver` is used to obtain a `ComponentFactory` for a given component type. The `ComponentFactory` is then used to create an instance of the component.
**How can I improve the performance of dynamic component creation?**: Cache the compiled `ComponentFactory` instances to avoid recompiling the same component multiple times. Also, optimize the template generation process and minimize the amount of DOM manipulation.

In essence, the ability to use and create dynamic templates for compiling dynamic components in Angular unlocks a realm of possibilities for building adaptable and user-centric applications. By understanding the intricacies of component factories, module compilation, and view container references, you can craft dynamic UIs that respond intelligently to varying data and user interactions. However, it's crucial to remember the importance of security and performance optimization to ensure a robust and efficient application. To further enhance your understanding, explore Angular's official documentation on dynamic component loading [\[Angular createComponent API\]](https://v15.angular.io/api/core/createComponent) and consider experimenting with different scenarios to solidify your grasp on these powerful concepts. What will you build with this newly acquired knowledge? Consider exploring advanced techniques like lazy loading dynamic modules to further optimize your applications, or dive into creating custom directives to enhance the flexibility of your dynamic templates. The possibilities are endless!

Question & Answer :
I want to dynamically create a template. This should be used to build a ComponentType at runtime and place (even replace) it somewhere inside of the hosting Component.

Until RC4 I was using ComponentResolver, but with RC5 I get the following message:

ComponentResolver is deprecated for dynamic compilation. Use ComponentFactoryResolver together with @NgModule/@Component.entryComponents or ANALYZE_FOR_ENTRY_COMPONENTS provider instead. For runtime compile only, you can also use Compiler.compileComponentSync/Async.

I found this document (Angular 2 Synchronous Dynamic Component Creation)

And understand that I can use either

Kind of dynamic ngIf with ComponentFactoryResolver. If I pass known components inside of @Component({entryComponents: [comp1, comp2], ...}) - I can use .resolveComponentFactory(componentToRender);
Real runtime compilation, with Compiler…

But the question is how to use that Compiler? The note above says that I should call: Compiler.compileComponentSync/Async - so how?

For example. I want to create (based on some configuration conditions) this kind of template for one kind of settings

<form> <string-editor [propertyName]="'code'" [entity]="entity" ></string-editor> <string-editor [propertyName]="'description'" [entity]="entity" ></string-editor> ...

and in another case this one (string-editor is replaced with text-editor)

<form> <text-editor [propertyName]="'code'" [entity]="entity" ></text-editor> ...

And so on (different number/date/reference editors by property types, skipped some properties for some users…). i.e. this is an example, the real configuration could generate much more different and complex templates.

The template is changing, so I cannot use ComponentFactoryResolver and pass existing ones… I need a solution with the Compiler.

NOTE: to get solution for previous version, check the history of this post

Similar topic is discussed here Equivalent of $compile in Angular 2. We need to use JitCompiler and NgModule. Read more about NgModule in Angular2 here:

Angular 2 RC5 - NgModules, Lazy Loading and AoT compilation

In a Nutshell

There is a working plunker/example (dynamic template, dynamic component type, dynamic module,JitCompiler, … in action)

The principal is:
1) create Template
2) find ComponentFactory in cache - go to 7)
3) - create Component
4) - create Module
5) - compile Module
6) - return (and cache for later use) ComponentFactory
7) use Target and ComponentFactory to create an Instance of dynamic Component

Here is a code snippet (more of it here) - Our custom Builder is returning just built/cached ComponentFactory and the view Target placeholder consume to create an instance of the DynamicComponent

// here we get a TEMPLATE with dynamic content === TODO var template = this.templateBuilder.prepareTemplate(this.entity, useTextarea); // here we get Factory (just compiled or from cache) this.typeBuilder .createComponentFactory(template) .then((factory: ComponentFactory<IHaveDynamicData>) => { // Target will instantiate and inject component (we'll keep reference to it) this.componentRef = this .dynamicComponentTarget .createComponent(factory); // let's inject @Inputs to component instance let component = this.componentRef.instance; component.entity = this.entity; //... });

This is it - in nutshell it. To get more details.. read below

TL&DR

Observe a plunker and come back to read details in case some snippet requires more explanation

Detailed explanation - Angular2 RC6++ & runtime components

Below description of this scenario, we will

create a module PartsModule:NgModule (holder of small pieces)
create another module DynamicModule:NgModule, which will contain our dynamic component (and reference PartsModule dynamically)
create dynamic Template (simple approach)
create new Component type (only if template has changed)
create new RuntimeModule:NgModule. This module will contain the previously created Component type
call JitCompiler.compileModuleAndAllComponentsAsync(runtimeModule) to get ComponentFactory
create an Instance of the DynamicComponent - job of the View Target placeholder and ComponentFactory
assign @Inputs to new instance (switch from INPUT to TEXTAREA editing), consume @Outputs

NgModule

We need an NgModules.

While I would like to show a very simple example, in this case, I would need three modules (in fact 4 - but I do not count the AppModule). Please, take this rather than a simple snippet as a basis for a really solid dynamic component generator.

There will be one module for all small components, e.g. string-editor, text-editor (date-editor, number-editor…)

@NgModule({ imports: [ CommonModule, FormsModule ], declarations: [ DYNAMIC_DIRECTIVES ], exports: [ DYNAMIC_DIRECTIVES, CommonModule, FormsModule ] }) export class PartsModule { }

Where DYNAMIC_DIRECTIVES are extensible and are intended to hold all small parts used for our dynamic Component template/type. Check app/parts/parts.module.ts

The second will be module for our Dynamic stuff handling. It will contain hosting components and some providers.. which will be singletons. Therefor we will publish them standard way - with forRoot()

import { DynamicDetail } from './detail.view'; import { DynamicTypeBuilder } from './type.builder'; import { DynamicTemplateBuilder } from './template.builder'; @NgModule({ imports: [ PartsModule ], declarations: [ DynamicDetail ], exports: [ DynamicDetail], }) export class DynamicModule { static forRoot() { return { ngModule: DynamicModule, providers: [ // singletons accross the whole app DynamicTemplateBuilder, DynamicTypeBuilder ], }; } }

Check the usage of the forRoot() in the AppModule

Finally, we will need an adhoc, runtime module.. but that will be created later, as a part of DynamicTypeBuilder job.

The forth module, application module, is the one who keeps declares compiler providers:

... import { COMPILER_PROVIDERS } from '@angular/compiler'; import { AppComponent } from './app.component'; import { DynamicModule } from './dynamic/dynamic.module'; @NgModule({ imports: [ BrowserModule, DynamicModule.forRoot() // singletons ], declarations: [ AppComponent], providers: [ COMPILER_PROVIDERS // this is an app singleton declaration ],

Read (do read) much more about NgModule there:

A template builder

In our example we will process detail of this kind of entity

entity = { code: "ABC123", description: "A description of this Entity" };

To create a template, in this plunker we use this simple/naive builder.

The real solution, a real template builder, is the place where your application can do a lot

// plunker - app/dynamic/template.builder.ts import {Injectable} from "@angular/core"; @Injectable() export class DynamicTemplateBuilder { public prepareTemplate(entity: any, useTextarea: boolean){ let properties = Object.keys(entity); let template = "<form >"; let editorName = useTextarea ? "text-editor" : "string-editor"; properties.forEach((propertyName) =>{ template += ` <${editorName} [propertyName]="'${propertyName}'" [entity]="entity" ></${editorName}>`; }); return template + "</form>"; } }

A trick here is - it builds a template which uses some set of known properties, e.g. entity. Such property(-ies) must be part of dynamic component, which we will create next.

To make it a bit more easier, we can use an interface to define properties, which our Template builder can use. This will be implemented by our dynamic Component type.

export interface IHaveDynamicData { public entity: any; ... }

A `ComponentFactory` builder

Very important thing here is to keep in mind:

our component type, build with our DynamicTypeBuilder, could differ - but only by its template (created above). Components’ properties (inputs, outputs or some protected) are still same. If we need different properties, we should define different combination of Template and Type Builder

So, we are touching the core of our solution. The Builder, will 1) create ComponentType 2) create its NgModule 3) compile ComponentFactory 4) cache it for later reuse.

An dependency we need to receive:

// plunker - app/dynamic/type.builder.ts import { JitCompiler } from '@angular/compiler'; @Injectable() export class DynamicTypeBuilder { // wee need Dynamic component builder constructor( protected compiler: JitCompiler ) {}

And here is a snippet how to get a ComponentFactory:

// plunker - app/dynamic/type.builder.ts // this object is singleton - so we can use this as a cache private _cacheOfFactories: {[templateKey: string]: ComponentFactory<IHaveDynamicData>} = {}; public createComponentFactory(template: string) : Promise<ComponentFactory<IHaveDynamicData>> { let factory = this._cacheOfFactories[template]; if (factory) { console.log("Module and Type are returned from cache") return new Promise((resolve) => { resolve(factory); }); } // unknown template ... let's create a Type for it let type = this.createNewComponent(template); let module = this.createComponentModule(type); return new Promise((resolve) => { this.compiler .compileModuleAndAllComponentsAsync(module) .then((moduleWithFactories) => { factory = _.find(moduleWithFactories.componentFactories , { componentType: type }); this._cacheOfFactories[template] = factory; resolve(factory); }); }); }

Above we create and cache both Component and Module. Because if the template (in fact the real dynamic part of that all) is the same.. we can reuse

And here are two methods, which represent the really cool way how to create a decorated classes/types in runtime. Not only @Component but also the @NgModule

protected createNewComponent (tmpl:string) { @Component({ selector: 'dynamic-component', template: tmpl, }) class CustomDynamicComponent implements IHaveDynamicData { @Input() public entity: any; }; // a component for this particular template return CustomDynamicComponent; } protected createComponentModule (componentType: any) { @NgModule({ imports: [ PartsModule, // there are 'text-editor', 'string-editor'... ], declarations: [ componentType ], }) class RuntimeComponentModule { } // a module for just this Type return RuntimeComponentModule; }

Important:

our component dynamic types differ, but just by template. So we use that fact to cache them. This is really very important. Angular2 will also cache these.. by the type. And if we would recreate for the same template strings new types… we will start to generate memory leaks.

`ComponentFactory` used by hosting component

Final piece is a component, which hosts the target for our dynamic component, e.g. <div #dynamicContentPlaceHolder></div>. We get a reference to it and use ComponentFactory to create a component. That is in a nutshell, and here are all the pieces of that component (if needed, open plunker here)

Let’s firstly summarize import statements:

import {Component, ComponentRef,ViewChild,ViewContainerRef} from '@angular/core'; import {AfterViewInit,OnInit,OnDestroy,OnChanges,SimpleChange} from '@angular/core'; import { IHaveDynamicData, DynamicTypeBuilder } from './type.builder'; import { DynamicTemplateBuilder } from './template.builder'; @Component({ selector: 'dynamic-detail', template: ` <div> check/uncheck to use INPUT vs TEXTAREA: <input type="checkbox" #val (click)="refreshContent(val.checked)" /><hr /> <div #dynamicContentPlaceHolder></div> <hr /> entity: {{entity | json}} </div> `, }) export class DynamicDetail implements AfterViewInit, OnChanges, OnDestroy, OnInit { // wee need Dynamic component builder constructor( protected typeBuilder: DynamicTypeBuilder, protected templateBuilder: DynamicTemplateBuilder ) {} ...

We just receive, template and component builders. Next are properties which are needed for our example (more in comments)

// reference for a <div> with #dynamicContentPlaceHolder @ViewChild('dynamicContentPlaceHolder', {read: ViewContainerRef}) protected dynamicComponentTarget: ViewContainerRef; // this will be reference to dynamic content - to be able to destroy it protected componentRef: ComponentRef<IHaveDynamicData>; // until ngAfterViewInit, we cannot start (firstly) to process dynamic stuff protected wasViewInitialized = false; // example entity ... to be recieved from other app parts // this is kind of candiate for @Input protected entity = { code: "ABC123", description: "A description of this Entity" };

In this simple scenario, our hosting component does not have any @Input. So it does not have to react to changes. But despite of that fact (and to be ready for coming changes) - we need to introduce some flag if the component was already (firstly) initiated. And only then we can start the magic.

Finally we will use our component builder, and its just compiled/cached ComponentFacotry. Our Target placeholder will be asked to instantiate the Component with that factory.

protected refreshContent(useTextarea: boolean = false){ if (this.componentRef) { this.componentRef.destroy(); } // here we get a TEMPLATE with dynamic content === TODO var template = this.templateBuilder.prepareTemplate(this.entity, useTextarea); // here we get Factory (just compiled or from cache) this.typeBuilder .createComponentFactory(template) .then((factory: ComponentFactory<IHaveDynamicData>) => { // Target will instantiate and inject component (we'll keep reference to it) this.componentRef = this .dynamicComponentTarget .createComponent(factory); // let's inject @Inputs to component instance let component = this.componentRef.instance; component.entity = this.entity; //... }); }

small extension

Also, we need to keep a reference to compiled template.. to be able properly destroy() it, whenever we will change it.

// this is the best moment where to start to process dynamic stuff public ngAfterViewInit(): void { this.wasViewInitialized = true; this.refreshContent(); } // wasViewInitialized is an IMPORTANT switch // when this component would have its own changing @Input() // - then we have to wait till view is intialized - first OnChange is too soon public ngOnChanges(changes: {[key: string]: SimpleChange}): void { if (this.wasViewInitialized) { return; } this.refreshContent(); } public ngOnDestroy(){ if (this.componentRef) { this.componentRef.destroy(); this.componentRef = null; } }

done

That is pretty much it. Do not forget to Destroy anything what was built dynamically (ngOnDestroy). Also, be sure to cache dynamic types and modules if the only difference is their template.

Check it all in action here

to see previous versions (e.g. RC5 related) of this post, check the history