SharePoint 2010 Lists and Libraries contain a new style of form called a Dialog which allows you to view and edit the metadata of a list or library. The forms can be modified by using InfoPath 2010 allowing you to provide validation, conditional formatting, calculations on fields and many other operations. You can modify the form using InfoPath 2010 by clicking the command on the ribbon as shown below:
Many people believe that you cannot modify the forms for an External List. There is very good reason to think that, since the Customize Form command does not display for an External List. The Customize List category on the list ribbon for an external list looks like the below:
There is another way of modifying the forms for list. You can navigate to the List Settings page and click on the Form Settings link from the General Settings section as shown below.
Unfortunately, clicking this option for an External list returns an error to say that InfoPath does not support customizing the form used for this list.
So how do you modify the forms?
1. Choose Site Actions, Edit in SharePoint Designer to modify the current site in SharePoint Designer 2010.
2. Click External Content Types from the left hand navigation pane in SharePoint Designer.
3. Click the External Content Type for the External List that you want to modify.
4. Click the Create Lists and Forms command on the ribbon.
5. A dialog box will display asking if you would like to replace the InfoPath form for the selected External List or create a new External List. In my example I am going to replace the InfoPath form for the External List as shown below. Click Ok.
6. Click External Lists from the left hand navigation pane.
7. Click the External List you just created or modified.
8. Click the Design Forms in InfoPath command on the ribbon.
9. The Form will display in InfoPath.
10. Choose the Page Design ribbon and select a page design as shown below:
11. Click the Company Name field and set the style to Title
12. Make the Phone number required by clicking the Phone Number Field and choosing the Home ribbon.
13. Click Add Rule, Is Blank, and then Validation Error to add a rule.
14. Set the error message to “Phone number cannot be blank”.
15. Click the save icon to save the form to the file system.
16. Publish the form to the list by clicking File, and then Publish, and then External List.
17. Click the Open this form in the browser link to navigate to your External List.
18. Test your changes by modifying an item in the External List
This is a simple example of how to modify the External List form in InfoPath 2010. You can of course do a lot more while in InfoPath.
I hope this helps.