What Snackbars do:
Snackbars are providing information on the state of the system. From material.io:
Snackbars provide updates on an app’s processes
Snackbars can be used to confirm success (or failure) of a process:
In this instance, the error is not a result of a wrong input on behalf of the user, but a system problem. A snackbar can have a single action to help correct this (such as retry).
vs. Form error display
Form error display is different: The system cannot let a user proceed until the user fixes some inputs they're attempting to submit.
1. Top of the form error messages:
These are often used to get users attention since it's obvious and visible real estate. They can consolidate (and link to) the individual errors found in the form:
2. Errors at the input level:
These are the specific inputs, often with a message providing information about why the input given is invalid (invalid ranges, wrong casing, etc.).
For forms, it’s a good practice to use 1 and 2 together, especially when you have forms that are somewhat long, or broken into sections.
Try to prevent these blocking form errors in the first place
- proper inline validation
- clear help text at the input level
- the forgiving format pattern
can prevent errors in the first place. But if users do receive errors, they should be told what they need to do to correct.