Using the Charts module
Step 1: Create the tabular format of the view
First to address the "if it's possible to list last 7 days date in views at all or not" part of your question, you really need to first work on getting the view created correctly. That's also what's recommended in the Bonus tip within Steps to create charts using the views UI, i.e.:
You may find it easier to start with a "Table" display and convert it to a chart display after setting up the data. It can be easier to visualize what the result of the chart will be if it's been laid out in a table first. ...
Step 2: Add the chart to your view
Do not try to start this step if you didn't first complete the prior step.
There is an issue which might help to answer this question, or at least to understand the challenge here. I.e. Graph node input over time (support date formatting on a continuous axis).
In Comment #3 of that issue is stated: 'The trouble here is that neither Views nor Date modules provide aggregation options for date-based fields.'.
Using the Quant module
If using the Charts module you can't get it to work (or don't want to consider the suggestions above), then you may want to look at the Quant module as an alternative. Here are some excerpts from its project page:
... provides an engine for producing quantitative, time-based analytics for virtually any Drupal component. Quant takes raw data about normal Drupal actions, such as node creation, and plots the activity over time, with the selected time being configurable. See the screenshot provided for a better understanding.
- Content creation
- Comment creation
- Content creation by type
- Aggregate content creation
- User creation
- Page views (requires Statistics)
- User shouts (requires Shoutbox)
- User point transactions (requires User Points)
- Group creation (requires Organic groups)
- Group joins (requires Organic groups)
- Invites sent (requires Invite)
- Invites accepted (requires Invite)
- Statuses shared (requires Facebook-style statuses)
- Private messages (requires Private message)
Especially the "Page views* chart that is provided might be close to what you're looking for.
Using the Visitors module
If you're looking for info related to visitors of a website (registered users is a subset of them ...), the Visitors module might be a valid alternative to consider also (and/or addition to the above modules). In this case, all you have to do is to enable the module and review the various out-of-the-box reports (which include charts created with the pChart library).
The demo site contains some sample reports (charts) available to anonymous users also. This demo site also shows some additional blocks with reports also created by the Visitors module.
In this specific case, you probably would want to look at the Days of week report (and chart). Note that, as a bonus, you can specify the desired date filter (from / to) also.
Refer to the Visitors community docu for some more details.
Extra reporting features can be enabled via these sub-modules:
- The Visitors GeoIP module, to also report about countries and cities.
- The Visitors Browscap module, providing statistics on visiting browsers.
Evaluating other charting modules
If none of the above modules would work in your case, then you might want to look at the "Comparison of Charting modules" documentation.
Disclosure: I'm a (co-)maintainer of all modules mentioned above (and original author of the comparison),
I hope this does not violate the site's policy on self-promotion.