How can I use/create dynamic template to compile dynamic Component with Angular 2.0?

Question

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 ho

Answer 1

EDIT - related to 2.3.0 (2016-12-07)

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) =>
    {
        // 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

1. create a module PartsModule:NgModule (holder of small pieces)
2. create another module DynamicModule:NgModule, which will contain our dynamic component (and reference PartsModule dynamically)
3. create dynamic Template (simple approach)
4. create new Component type (only if template has changed)
5. create new RuntimeModule:NgModule. This module will contain the previously created Component type
6. call JitCompiler.compileModuleAndAllComponentsAsync(runtimeModule) to get ComponentFactory
7. create an Instance of the DynamicComponent - job of the View Target placeholder and ComponentFactory
8. 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:

• Angular 2 RC5 - NgModules, Lazy Loading and AoT compilation
• Angular Modules documentation

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 = "
";
      let editorName = useTextarea 
        ? "text-editor"
        : "string-editor";
        
      properties.forEach((propertyName) =>{
        template += `
          <${editorName}
              [propertyName]="'${propertyName}'"
              [entity]="entity"
          >`;
      });
  
      return template + "
";
    }
}

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} = {};
  
public createComponentFactory(template: string)
    : Promise> {    
    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.

. 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: `

  check/uncheck to use INPUT vs TEXTAREA:
  

  
  

  entity: 
{{entity | json}}

`,
})
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 
 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;

// 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) =>
    {
        // 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