在Parse.com上保存检索声音

Question

I am trying to download some short sound file on Parse.com in an iOS application. The file has previously been saved using the following code:

    NSData *soundData = [NSData dataWithContentsOfURL:myURL];
    parse_Sound = [PFFile fileWithName:@"XXYYZZ"
                                  data:soundData];
    [parse_Sound saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
        if (!succeeded) {
                NSLog(@"sound-upload NG”);
        } else {
                NSLog(@"sound-upload OK");
            }];
        }
    }];

Seeing the message on the debugging console, it appearently works. Now what kind of code do I need to run to retrieve(download) the sound file? I have browsed the net, but found nothing clear and working.

Answer 1

You need to keep a reference to that file somewhere (ideally in a column of the PFObject it belongs to).

If you don't keep a reference you're out of luck and you can't retrieve already uploaded files that have no association to any object.

I suggest you read through the Parse documentation for files on iOS https://www.parse.com/docs/ios_guide#files/iOS

Answer 2

To get data back from the server you need to need to run a query asking for that object but you haven't associated the uploaded file with a column in any Class yet. Uploading a PFFile is iOS is a two step process:

1) Upload the PFFile to the server

2) In the callback associated the PFFile with a column in a data object

NSData *soundData = [NSData dataWithContentsOfURL:myURL];
    parse_Sound = [PFFile fileWithName:@"XXYYZZ"
                                  data:soundData];
    [parse_Sound saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
        if (!succeeded) {
                NSLog(@"sound-upload NG”);
        } else {
                NSLog(@"sound-upload OK");

                PFObject *soundStuff = [PFObject objectWithClassName:@"Sounds"];

                soundStuff[@"soundFile"] = parse_Sound;
                [soundStuff saveInBackground];

            }];
        }
    }];

Now to get the data back you would run a query on the Sounds class that will have the sound data in the soundFile column:

PFQuery *query = [PFQuery queryWithClassName:@"Sounds"];
[query whereKey:@"someKey" equalTo:@"someValue"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
  if (!error) {
    // The find succeeded.

    // Do something with the found objects
    for (PFObject *object in objects) {
        NSLog(@"%@", object.objectId);
        PFFile *soundFile = object[@"soundFile"];
        NSData *soundData = [soundFile getData];

    }
  } else {
    // Log details of the failure
    NSLog(@"Error: %@ %@", error, [error userInfo]);
  }
}];

I haven't tested any of this code but it at least demonstrates the steps needed and should get you started.

Here are the examples from the documentation :

PFObject *jobApplication = [PFObject objectWithClassName:@"JobApplication"]
jobApplication[@"applicantName"] = @"Joe Smith";
jobApplication[@"applicantResumeFile"] = file;
[jobApplication saveInBackground];

Then to get the data back:

PFFile *applicantResume = anotherApplication[@"applicantResumeFile"];
NSData *resumeData = [applicantResume getData];

Notice that file is being associated with the applicantResumeFile column of the JobApplication class so that the file data can be retrieved in queries.