How to Set a Default Value for mat-select in Angular Material

Struggling to set a default value for the dropdown in Angular Material's `mat-select`? Explore this step-by-step guide to effectively implement default values in your dropdown.
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How to Set a Default Value for mat-select in Angular Material

When working with Angular applications, you might encounter situations where you need to set a default value for dropdowns, particularly when using mat-select from Angular Material. This can often lead to confusion if the default value doesn’t populate as expected. In this post, we will address this common problem and guide you through the solution.

Understanding the Problem

In your Angular component, you created a dropdown using mat-select, but noticed that it didn't have a default value. You attempted to set a value like this:

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

However, despite your efforts, the dropdown did not show the intended default value of mydefaultvalue.

The Solution: Binding Using compareWith

To achieve the desired functionality, we need to use Angular's compareWith property. This property allows you to define a function that determines how values are compared — thereby enabling the setting of default values effectively.

Step 1: Update HTML Template

Make the following changes to your HTML template:

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

Key Changes Made:

Use [(ngModel)] instead of value="{{...}}" to bind your selected value properly.

Add [compareWith] to bind to a comparison function that we will define in the TypeScript file.

Step 2: Define the Comparison Function

Now, you need to define the comparison function in your TypeScript file. Add this method to your component:

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

Explanation of the Comparison Function:

The function checks if both objects are present.

It then compares their id properties (or any identifier you are using).

If they are equal, it returns true, allowing Angular to recognize the selected default item in the dropdown.

Confirming Your Default Value is Set

Finally, ensure that your dropdownSelectedName is set correctly in the component’s ngOnInit:

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

Important Note:

Make sure the dropdownSelectedName corresponds to an actual item in your itemList, and that it correctly reflects the identifier checked in your compareFn.

Conclusion

By following the steps outlined above, you will successfully set a default value for the mat-select dropdown in Angular Material. Utilizing the compareWith property is key to effective dropdown management in Angular, ensuring that your application is both user-friendly and functional.

Feel free to reach out with any questions or issues you may encounter. Happy coding!

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