How to download google files in google drive sdk? - objective-c

Question

In this way, I download a image successfully:
GTLServiceDrive *drive = ...;
GTLDriveFile *file = ...;
NSString *url = [NSString stringWithFormat:#"https://www.googleapis.com/drive/v3/files/%#?alt=media",file.identifier];
GTMSessionFetcher *fetcher = [drive.fetcherService fetcherWithURLString:url];
[fetcher beginFetchWithCompletionHandler:^(NSData *data, NSError *error) {
if (error == nil) {
NSLog(#"Retrieved file content");
// Do something with data
} else {
NSLog(#"An error occurred: %#", error);
}
}];
the document of google drive sdk tell me to download a pdf or google docs should use another url:
NSString *url = [NSString stringWithFormat:#"https://www.googleapis.com/drive/v3/files/%#/export?alt=media&mimeType=application/pdf",file.identifier];
but I failed, error is this:
{
"error": {
"errors": [
{
"domain": "global",
"reason": "badRequest",
"message": "Bad Request"
}
],
"code": 400,
"message": "Bad Request"
}
}

Answer 1

In downloading file make sure your app must be authorized with a scope that allows reading of file content. For example, an app using the drive.readonly.metadata scope would not be authorized to download the file contents. Users with edit permission may restrict downloading by read-only users by setting the viewersCanCopyContent field to true.
There is another way to download a file by using the partial download. It involves downloading only a specified portion of a file. You can specify the portion of the file you want to dowload by using a byte range with the Range header.
This SO question is using partial download. I think it can help you.
This code demonstrate how to download a Google Document in PDF format.
String fileId = "1ZdR3L3qP4Bkq8noWLJHSr_iBau0DNT4Kli4SxNc2YEo";
OutputStream outputStream = new ByteArrayOutputStream();
driveService.files().export(fileId, "application/pdf")
.executeMediaAndDownloadTo(outputStream);