Custom Form Components in Angular: Avoid These Common Mistakes

In Angular development, creating custom form components is a powerful way to encapsulate logic and maintain reusable UI elements. However, when integrating these components into Angular’s form ecosystem, many developers ask:
Should I use ControlValueAccessor , or is *FormGroupDirective * more appropriate for this use case?
The answer depends on the structure of your component and how it interacts with the Angular forms API.

✅ Use ControlValueAccessor for Single Form Control Components

If your custom component represents a single form control — such as an input field, toggle switch, dropdown, or similar —the correct and most idiomatic approach is to implement the *ControlValueAccessor * interface.
This allows Angular to treat your custom component as if it were a native input element, meaning you can use it seamlessly with FormControl, FormGroup, ngModel, etc.

Example Use Case

You're building a custom input with a prefix and suffix icon:

<my-custom-input formControlName="username"></my-custom-input>

Since this component only handles a single value, ControlValueAccessor is the ideal solution. You implement writeValue, registerOnChange, and registerOnTouched to hook it into Angular’s change detection and form updates.

🧠 Use FormGroupDirective (or ControlContainer) for Multi-Control Components

If your custom component is a composite control that internally manages multiple form controls, then using ControlValueAccessor is not suitable.

This is common for components like:

• A date range picker that has fromDate and toDate
• A time range selector with startTime and endTime
• An address form that collects street, city, and postal code

Why ControlValueAccessor Doesn’t Fit

ControlValueAccessor is designed to bind a single value to a form control. But in a date range picker, you're managing two values (from and to), each of which should be independently controllable, validated, and possibly bound to different parts of the parent form.

Solution: Accept Multiple FormControls via Inputs
You can structure your component like this:

<my-date-range 
  [fromControl]="startDate" 
  [toControl]="endDate">
</my-date-range>

In this pattern:

• The parent FormGroup manages both controls.
• The component accepts the FormControls as @Input() bindings.
• Inside the component, you use FormControlDirective or NgControl for validation display, state handling, etc.

Bonus Tip: Avoid Mixing the Two

If you try to mix ControlValueAccessor and manually managed multiple controls inside the same component, you’ll run into conflicts and validation issues. Keep it clean: choose one approach based on your component’s intent.

Final Thoughts

Understanding when to use ControlValueAccessor vs FormGroupDirective is essential for writing clean, scalable Angular forms.

• For simple, single-value inputs, implement ControlValueAccessor.
• For composite components managing multiple fields, pass FormControls or FormGroup directly and manage them internally.

This mental model will save you from form headaches and help you build highly reusable and Angular-friendly form components.