Which action is required to validate that mandatory input fields are filled before submitting?

To ensure that mandatory input fields are filled before submitting a form, checking the Form.Valid property is a critical action. This property evaluates whether all the required input fields meet their validation criteria before any submission takes place. By referencing the Form.Valid property, developers can effectively ascertain that all mandatory inputs are filled, thus preventing any submission attempt that could lead to incomplete or erroneous data processing.

The Form.Valid property acts as a centralized validation mechanism, ensuring the user cannot proceed unless all conditions are satisfied. Only after confirming that this property returns true can developers proceed with operations like data submission, ensuring data integrity and enhancing user experience.

In contrast, calling validations in the screen action flow or using client actions may involve additional programming and complexity without directly addressing the requirement for field completeness. Similarly, submitting after handling invalid inputs does not prevent errors in the first place, as it allows submissions even when fields are not filled correctly, leading to potential data issues.