mat-form-field must contain a MatFormFieldControl

📝 Title: Troubleshooting the "mat-form-field must contain a MatFormFieldControl" Error

👋 Hey there, tech enthusiasts! Are you in the process of building your own form-field components using Material Design's components? 🛠️ Are you encountering the frustrating "mat-form-field must contain a MatFormFieldControl" error? 😫 Don't worry, we've got you covered! In this guide, we'll walk you through common issues related to this error and provide you with easy solutions. Let's dive in! 💪

💡 Understanding the Error When working with custom form-field components, you might come across the "mat-form-field must contain a MatFormFieldControl" error. This error is typically thrown when the mat-form-field element does not directly contain a matInput-field control. However, in some cases, the control is nested within an ng-content projection. Let's take a closer look at an example scenario to better understand this issue.

👉 Here's an example of how a custom form-field component might be implemented:

<mat-form-field>
    <ng-content></ng-content>
    <mat-hint align="start"><strong>{{hint}}</strong></mat-hint>
    <mat-hint align="end">{{message.value.length}} / 256</mat-hint>
    <mat-error>This field is required</mat-error>
</mat-form-field>
<field hint="hint">
    <input matInput 
    [placeholder]="placeholder" 
    [value]="value"
    (change)="onChange($event)"
    (keydown)="onKeydown($event)"
    (keyup)="onKeyup($event)"
    (keypress)="onKeypress($event)">
</field>
<textbox value="test" hint="my hint"></textbox>

👉 When rendered, the custom component looks like this:

<textbox placeholder="Personnummer/samordningsnummer" value="" ng-reflect-placeholder="Personnummer/samordningsnummer">
  <field>
    <mat-form-field class="mat-input-container mat-form-field">
      <div class="mat-input-wrapper mat-form-field-wrapper">
        <div class="mat-input-flex mat-form-field-flex">
          <div class="mat-input-infix mat-form-field-infix">
            <input _ngcontent-c4="" class="mat-input-element mat-form-field-autofill-control" matinput="" ng-reflect-placeholder="Personnummer/samordningsnummer" ng-reflect-value="" id="mat-input-2" placeholder="Personnummer/samordningsnummer" aria-invalid="false">
            <span class="mat-input-placeholder-wrapper mat-form-field-placeholder-wrapper"></span>
          </div>
        </div>
        <div class="mat-input-underline mat-form-field-underline">
          <span class="mat-input-ripple mat-form-field-ripple"></span>
        </div>
        <div class="mat-input-subscript-wrapper mat-form-field-subscript-wrapper"></div>
      </div>
    </mat-form-field>
  </field>
</textbox>

❗ The Error Despite the control being present, you might encounter the infamous "mat-form-field must contain a MatFormFieldControl" error in your console. It's important to note that this error is thrown due to the ControlComponent not being directly present within the mat-form-field element.

🔧 Easy Solutions Don't panic! We have a couple of easy solutions for you to resolve this error once and for all. 💪

1️⃣ Solution 1: Reordering Elements One simple solution is to reorder the elements within your custom form-field component. Ensure that the ng-content projection containing the matInput element appears first within the mat-form-field element. Following the example above, modify your code as follows:

<field hint="hint">
    <mat-form-field>
        <ng-content></ng-content>
        <mat-hint align="start"><strong>{{hint}}</strong></mat-hint>
        <mat-hint align="end">{{message.value.length}} / 256</mat-hint>
        <mat-error>This field is required</mat-error>
    </mat-form-field>
</field>

2️⃣ Solution 2: Using MatFormFieldControl Another option is to implement the MatFormFieldControl interface in your custom component. By doing this, you can explicitly declare the matInput as the MatFormFieldControl within your component class. This tells Angular to treat the element as a valid control within the mat-form-field. Update your code accordingly:

import { ..., MatFormFieldControl } from '@angular/material/form-field';

@Component({
  ...
  providers: [
    { provide: MatFormFieldControl, useExisting: CustomFormFieldComponent },
  ],
})
export class CustomFormFieldComponent implements MatFormFieldControl<any> {
  // Implement the required properties and methods
  ...
}

🎉 Call-to-Action: Share your Success Stories! Now that you've learned how to tackle the "mat-form-field must contain a MatFormFieldControl" error, it's time to put your skills into action! 🚀 Have you successfully resolved this error? Share your experience and let us know how you overcame this hurdle in the comments below. You never know who might find your insights helpful! 😊

🔗 Explore and Experiment Ready to explore and experiment? Check out this StackBlitz with the problem scenario provided in the original question: StackBlitz Demo. Feel free to modify the code and see the error disappear once you apply the solutions provided in this guide.

That's a wrap, folks! We hope this guide has helped you understand and troubleshoot the "mat-form-field must contain a MatFormFieldControl" error. Remember, we're here to support you on your tech journey. Stay curious and keep coding! 💻🌟