App Inventor includes a Storage File component that can be used for reading and writing. One use of this component can be for reading CSV (Comma Separated File) as key value pairs.
Assume you have a a file called myDataFile.csv with contents that includes authors (key) and books (values) like below. Note that in below example, the value can be varible-size tokenized string (string with multiple values):
Hossein,Absolute App Inventor 2|Amazon|Google Play Book|Apple Book Store
Dave Wolber,App Inventor|Google
The code below shows how we can use a TEXT field to get a user-entered key and then search the data-file and return the search data into another TEXT filed. The code below will loop through the tokenized string value and print each token.