Скачать или смотреть Resolving the mat-table Error: "Missing definitions for header, footer, and row"

Learn how to fix the `mat-table` error in Angular 9 related to missing definitions for headers, footers, and rows, ensuring your table renders properly.
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This video is based on the question https://stackoverflow.com/q/65763718/ asked by the user 'satish' ( https://stackoverflow.com/u/9420149/ ) and on the answer https://stackoverflow.com/a/65763804/ provided by the user 'Kishan' ( https://stackoverflow.com/u/2422788/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Dealing with the mat-table Error in Angular

If you're developing an Angular application and working with mat-table, you might have encountered a frustrating error that reads:

[[See Video to Reveal this Text or Code Snippet]]

This often signifies that the Angular Material table is unable to ascertain the structure of your data and how to render it effectively. In this guide, we'll break down the cause of this issue and guide you through the steps to resolve it so that your table can render correctly.

Understanding the Problem

When creating a mat-table, you need to provide not only the data source (i.e., the data to be displayed) but also the definitions for the headers and rows that will organize this data. Without these definitions, Angular cannot determine which columns to display, leading to the aforementioned error. In a nutshell, your code is missing essential elements that inform mat-table how to handle the data you're feeding it.

Step-by-Step Solution

To effectively resolve the error, follow these clear steps:

1. Add Row Definitions

You need to include row definitions in your mat-table to let Angular know how to display your rows and headers. This includes adding the <mat-header-row> and <mat-row> components to your code. Here's how it looks:

[[See Video to Reveal this Text or Code Snippet]]

2. Define the displayedColumns Variable

Next, you must define which columns should be displayed in your table. This is done by creating a variable in your component class, displayedColumns, which is an array of strings that match your column definitions. Update your TypeScript code as follows:

[[See Video to Reveal this Text or Code Snippet]]

3. Verify Your Data

Before running your application, ensure that the data returned from your API has a title attribute in each object as you have mentioned in your scenario. A successful subscription to your API should yield structured data that your mat-table can render accurately.

Conclusion

By following the steps outlined above—specifying row definitions and defining which columns should be displayed—you should be able to resolve the "Missing definitions" error associated with mat-table. Angular Material provides rich and flexible table components, making it a snap to display data once you’ve set up the necessary configurations correctly.

If you continue to encounter issues, double-check your HTML for typos or mismatches in your column definitions, and ensure your service is returning the expected data format. Happy coding!