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ngForOf Not Working on tr: Angular Error Fix

By Filip on 10/05/2024

Learn how to resolve the common Angular error "'Can't bind to 'ngForOf' since it isn't a known property of 'tr'" and get your code working again.

ngForOf Not Working on tr: Angular Error Fix

Table of Contents

Introduction

The error "Can't bind to 'ngForOf' since it isn't a known property of '...'" in Angular indicates that the template engine cannot find the *ngFor directive. This usually happens for a few common reasons: Make sure you have imported the necessary modules, declared your component correctly, avoided typos, and are using a supported Angular version. If you're still facing issues, provide code snippets, module structure, and your Angular version for further assistance.

Step-by-Step Guide

The error "Can't bind to 'ngForOf' since it isn't a known property of '...'" in Angular indicates that the template engine cannot find the *ngFor directive. This usually happens for a few common reasons:

1. BrowserModule or CommonModule Not Imported

  • The *ngFor directive is part of Angular's core directives, which are available through either BrowserModule or CommonModule.
  • BrowserModule is intended for the root module of your application (usually AppModule).
  • CommonModule is for all other feature modules.

Example (app.module.ts):

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppComponent } from './app.component';

@NgModule({
  declarations: [AppComponent],
  imports: [BrowserModule], // Make sure BrowserModule is imported
  bootstrap: [AppComponent]
})
export class AppModule { }

Example (feature.module.ts):

import { CommonModule } from '@angular/common';
import { NgModule } from '@angular/core';

import { FeatureComponent } from './feature.component';

@NgModule({
  declarations: [FeatureComponent],
  imports: [CommonModule], // Make sure CommonModule is imported
  exports: [FeatureComponent]
})
export class FeatureModule { }

2. Component Not Declared in a Module

  • Every Angular component must belong to an NgModule. If you've created a new component and are trying to use *ngFor within its template, ensure it's declared in the declarations array of its corresponding module.

Example:

// ... other imports ...
import { MyComponent } from './my.component';

@NgModule({
  declarations: [
    AppComponent,
    MyComponent // Declare your component here
  ],
  // ... other module properties ...
})
export class AppModule { }

3. Typos and Case Sensitivity

  • Double-check for any typos in:
    • The directive name: It should be *ngFor (case-sensitive).
    • The ngForOf property: It should be exactly ngForOf.

Example (Correct Usage):

<ul>
  <li *ngFor="let item of items">{{ item }}</li>
</ul>

4. Outdated Angular Version

  • While rare, issues with *ngFor might arise from using a very outdated Angular version. Ensure you're using a recent, supported version.

Troubleshooting Steps:

  1. Check Imports: Verify that you've imported BrowserModule in your root module and CommonModule in any feature modules where you're using *ngFor.
  2. Component Declaration: Make sure the component where you're using *ngFor is declared in the declarations array of its module.
  3. Inspect for Typos: Carefully examine your code for any typos in the directive name or the ngForOf property.
  4. Restart Development Server: Sometimes, simply restarting your Angular development server can resolve strange errors.

If you've followed these steps and are still encountering the error, provide the following information for more specific assistance:

  • Relevant Code Snippets: Share your component's HTML template and TypeScript code.
  • Module Structure: Describe how your modules are organized and which module your component belongs to.
  • Angular Version: Specify the version of Angular you're using.

Code Example

This code snippet explains how to troubleshoot the Angular error "Can't bind to 'ngForOf' since it isn't a known property of '...'". The error happens when you use the *ngFor directive without importing CommonModule in your Angular module. The solution is to import CommonModule into the module where the component using *ngFor is declared. This makes the directive available for use in your component's template. The example provides code snippets to illustrate the error and the correction.

This example will showcase a simplified scenario where the error occurs and how to fix it.

File Structure:

angular-app/
├── src/
│   ├── app/
│   │   ├── app.module.ts
│   │   ├── app.component.ts
│   │   └── items/
│   │       ├── items.component.ts
│   │       └── items.component.html
│   └── main.ts
└── ...

1. The Error:

Let's say we have a component items.component.ts that tries to use *ngFor without importing CommonModule:

items.component.ts:

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

@Component({
  selector: 'app-items',
  templateUrl: './items.component.html'
})
export class ItemsComponent {
  items = ['Item 1', 'Item 2', 'Item 3'];
}

items.component.html:

<ul>
  <li *ngFor="let item of items">{{ item }}</li>
</ul>

items.module.ts (Incorrect):

import { NgModule } from '@angular/core';
import { ItemsComponent } from './items.component';

@NgModule({
  declarations: [ItemsComponent],
  exports: [ItemsComponent]
})
export class ItemsModule { }

This will result in the error: "Can't bind to 'ngForOf' since it isn't a known property of 'li'."

2. The Solution:

To fix this, we need to import CommonModule into items.module.ts:

items.module.ts (Corrected):

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common'; // Import CommonModule
import { ItemsComponent } from './items.component';

@NgModule({
  declarations: [ItemsComponent],
  imports: [CommonModule], // Add CommonModule to imports
  exports: [ItemsComponent]
})
export class ItemsModule { }

3. Additional Notes:

  • Make sure ItemsModule is imported into your AppModule.
  • Always double-check for typos in directive names and properties.
  • If you're still facing issues, provide the complete code snippets and your Angular version for further assistance.

This example demonstrates a common scenario where the error occurs. By ensuring the correct imports and declarations, you can resolve this issue and use the *ngFor directive effectively in your Angular applications.

Additional Notes

Understanding the Root Cause:

  • The error fundamentally means Angular can't recognize *ngFor as a valid directive within your component's template. This is almost always related to the directive not being accessible due to module imports or component declarations.

Beyond CommonModule and BrowserModule:

  • While CommonModule and BrowserModule are the most common sources of *ngFor, remember that any module exporting directives can potentially make *ngFor available. If you have custom modules with directives, ensure they are correctly imported and exported.

Angular CLI and Module Management:

  • If you're using the Angular CLI, it usually handles importing BrowserModule into AppModule and generating modules for new components. However, it's still essential to understand these concepts in case you encounter issues or are working with a manually configured project.

Lazy Loading and Shared Modules:

  • Be mindful of lazy-loaded modules. If you're using *ngFor within a lazy-loaded module, ensure CommonModule is imported into that module's imports, not just in your shared modules.

Debugging Tips:

  • Browser Console: Pay close attention to the browser console for any additional error messages that might provide more context.
  • Angular Language Service: If you're using an IDE with Angular Language Service, it might highlight the error directly in your template, offering helpful suggestions.

Best Practices:

  • Modular Design: Organize your application into well-defined modules to manage dependencies effectively and avoid potential conflicts.
  • Code Review: Regular code reviews can help catch these common errors early on.

Remember: This error is usually straightforward to fix once you understand the underlying cause. By following the troubleshooting steps and keeping these additional notes in mind, you can quickly resolve it and continue building your Angular applications.

Summary

This error means Angular can't find the *ngFor directive, essential for looping through data in templates. Here's a breakdown of common causes and how to fix them:

Causes:

  1. Missing Module Imports:

    • Solution: Ensure you've imported:
      • BrowserModule in your root module (AppModule).
      • CommonModule in all other feature modules using *ngFor.

  2. Component Not Declared:

    • Solution: Declare the component using *ngFor within the declarations array of its corresponding module.

  3. Typos:

    • Solution: Double-check for typos in:
      • Directive name: *ngFor (case-sensitive).
      • Property: ngForOf (case-sensitive).

  4. Outdated Angular Version:

    • Solution: Update to a recent, supported Angular version.

Troubleshooting Steps:

  1. Verify module imports (BrowserModule / CommonModule).
  2. Confirm component declaration in the module.
  3. Inspect for typos in *ngFor and ngForOf.
  4. Restart your Angular development server.

Need More Help?

Provide these details for further assistance:

  • Relevant code snippets (HTML template and TypeScript).
  • Module structure and component location.
  • Your Angular version.

Conclusion

By addressing these common causes and following the troubleshooting steps, you can effectively resolve the "Can't bind to 'ngForOf'" error and unlock the power of the *ngFor directive for dynamic rendering in your Angular applications. Remember to pay close attention to module imports, component declarations, and potential typos. If you encounter persistent issues, providing specific code snippets, module structure, and your Angular version will enable others to assist you more effectively.

References

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