Getting items from another book, unlike another sheet in one book, is similar. This is a two-step process. First, you need to import the data that you want to use for the validation elements into the workbook where you want to use it, then plug it in as described in @ uselink126's answer.
Example: Workbook 2 contains a list of fruit names in a specific order. For reading, a named range of Fruits been assigned to the list, but this is optional. Workbook 1 , in Sheet 1 there is a column of cells in which we want to populate the drop-down list with elements from book 2.
Step 1 - Import Data
Add another sheet to book 1 and paste the following formula into cell A1:
=ImportRange("<key>","Sheet1!Fruits")
where <key> is the unique identifier of the Google documents assigned when creating the spreadsheet. In this example, items are sorted alphabetically as part of the import, and for this you must enter:
=Sort (ImportRange("<key>","Sheet1!Fruits"), 1, true)
1, means column 1 is sorting, true means ascending sorting. The cells in column 1 should be filled with sorted fruits.
Step 2 - Send data validation to the imported list
In Workbook 1, Sheet 1, select the cells in which you want the fruits to be their drop-down data source. - Right-click the selection and select Data Validation from the menu. Set Criteria to List from a range and enter Sheet2!A1:A20
What is it. Drop-down chevrons should appear in these cells, and when you click on them, a list of fruits appears.
Please note that this is βliveβ - adding a fruit item to the Workbook 2 list will also add it to the drop-down list.