Question

Is there any way to run my app when the user taps on an e-mail attachment, so I can access the attached file?

What I want to do is implement some kind of backup / restore for app data:

1. The user sends an e-mail with an attached data file that has a special extension (I will be using the new iPhone 3.0 message composer class)
2. If the user loses his data, they will be able to go to their e-mail box and open the last e-mail they sent with the app data file
3. Then they simply tap on the attached file, which causes my app to run and restore from that file

Is it technically possible to perform the last step?

Thanks

Answer 1

Mobile Orchard has a great tutorial, describing how to restore your applications database through Custom URL handlers of a serialized SQL Lite database:
Lite To Paid iPhone Application Data Migrations With Custom URL Handlers

(paraphrased instructions from the article)

1. Setup a custom URL handler in your project’s Info.plist Setup a custom URL handler http://www.mobileorchard.com/wp-content/uploads/2009/01/result.png

2. In your email message convert your database or application data to NSData base64, and include it in a URL
   For example:

   [NSString stringWithFormat: @”myapplication://localhost/importDatabase?%@”,encodedStringData]

3. Add a handleOpenURL method to your AppDelegate implementation

Example AppDelegate Implementation:

#import "GTMBase64.h"

- (BOOL)application:(UIApplication *)application handleOpenURL:(NSURL *)url {
    if([@"/importDatabase" isEqual:[url path]]) {
        NSString *query = [url query];
        NSString *importUrlData = [GTMBase64 webSafeDecodeString:query];

        // NOTE: In practice you will want to prompt the user to confirm before you overwrite their files!
        [importUrlData writeToFile:@"/path/to/FullApplication/Documents/file" atomically:YES];
        return YES;
    }
    return NO;
}

Mobile Orchard on File size limitations:

We have transferred files of up to
100k this way, and the size of a URL
string is theoretically only limited
by available memory. That said, this
approach is most suitable for
applications with small to medium size
data transfer requirements. Best of
all though, it can be easily used for
SQLite databases, XML files, text
files, or even extended to handled
compressed archives.