Troubleshooting Angular Material Dialogs: Step-by-Step Guide to Fix "Did you add it to @NgModule.entryComponents?"

This error arises when you attempt to use a component as a dialog within Angular Material's MatDialog service, but Angular cannot locate the necessary information to create the dialog dynamically.

Breakdown:

• Angular2 (or Angular): The core web framework for building dynamic client-side web applications.
• Angular Material: A collection of pre-built UI components that integrate seamlessly with Angular, providing a consistent and Material Design-based look and feel.

@NgModule.entryComponents:

• An array property within the @NgModule decorator in Angular.
• It instructs Angular about components that need to be dynamically created (often at runtime) within the module.
• This is crucial for dialogs because MatDialog creates them on demand when you open a dialog.

Resolving the Error:

3. Add to entryComponents: Within the @NgModule decorator of that module, include the dialog component in the entryComponents array. Here's an example:

   import { NgModule } from '@angular/core';
   import { CommonModule } from '@angular/common';
   import { MyDialogComponent } from './my-dialog.component'; // Your dialog component
   import { MatDialogModule } from '@angular/material/dialog'; // Import for MatDialog
   
   @NgModule({
     imports: [
       CommonModule,
       MatDialogModule
     ],
     declarations: [MyDialogComponent], // Declare the dialog component
     entryComponents: [MyDialogComponent] // Add to entryComponents
   })
   export class MyModule { }
   

Explanation:

By adding the dialog component to entryComponents, Angular is informed that this component might be used dynamically (e.g., within a dialog) and should have the necessary factory registered for its creation.

Additional Considerations:

• If your dialog component is in a lazy-loaded module, ensure that module is loaded when attempting to open the dialog.

my-dialog.component.ts (Dialog component):

import { Component } from '@angular/core';

@Component({
  selector: 'app-my-dialog',
  templateUrl: './my-dialog.component.html',
  styleUrls: ['./my-dialog.component.css']
})
export class MyDialogComponent {
  // ... Your dialog content logic
}

my-module.component.ts (Module using the dialog, but missing entryComponents):

import { Component, OnInit } from '@angular/core';
import { MatDialog } from '@angular/material/dialog';
import { MyDialogComponent } from './my-dialog.component'; // Import the dialog component

@Component({
  selector: 'app-my-module',
  templateUrl: './my-module.component.html',
  styleUrls: ['./my-module.component.css']
})
export class MyModuleComponent implements OnInit {

  constructor(private dialog: MatDialog) {}

  ngOnInit() {}

  openDialog() {
    this.dialog.open(MyDialogComponent); // This will cause the error
  }
}

my-module.module.ts (Missing entryComponents):

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { MyModuleComponent } from './my-module.component';
import { MatDialogModule } from '@angular/material/dialog'; // Import MatDialogModule

@NgModule({
  imports: [
    CommonModule,
    MatDialogModule
  ],
  declarations: [MyModuleComponent], // Only declares MyModuleComponent
  exports: [MyModuleComponent]
})
export class MyModuleModule { }

In this scenario, attempting to open MyDialogComponent using MatDialog will result in the error because MyModule doesn't have it listed in entryComponents.

Scenario 2: Correct entryComponents Usage

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { MyModuleComponent } from './my-module.component';
import { MyDialogComponent } from './my-dialog.component'; // Import the dialog component
import { MatDialogModule } from '@angular/material/dialog'; // Import MatDialogModule

@NgModule({
  imports: [
    CommonModule,
    MatDialogModule
  ],
  declarations: [MyModuleComponent, MyDialogComponent], // Declare both components
  entryComponents: [MyDialogComponent] // Add MyDialogComponent to entryComponents
})
export class MyModuleModule { }

By adding MyDialogComponent to entryComponents in MyModule, Angular is aware of this component's potential dynamic usage and can create it successfully when the dialog is opened.

1. Component Pre-creation (Limited Use Case):

   • However, this approach has limitations:

     • It's not suitable for complex dialogs requiring dynamic content.
     • Pre-creating multiple instances can become memory-intensive.

2. Lazy Loading (Advanced):

3. Third-Party Dialog Libraries (Consider Alternatives):