I am wondering how to do the following correctly: I have a method that is to return an NSData
object. It gets the NSData
object from a UIDocument
. The NSData
object can get large, so I want to make sure it is fully loaded before the response starts. I would therefore like to return the value of the method from within the block itself. So something like this:
- (NSData*)getMyData {
MyUIDocument *doc = [[MyUIDocument alloc] initWithFileURL:fileURL];
[doc openWithCompletionHandler:^(BOOL success) {
if (success) {
return doc.myResponseData; // this is to be the return for the method not the block
}
}];
}
This causes an error because the return
apparently refers to the block
's return
.
How can I accomplish this without having to make a thread blocking wait/while loop?
Thanks.
You can't. Embrace the fact that what you're trying to do is asynchronous and add a completion block parameter to your getMyData
method which is called when the inner completion handler is called. (And remove the return
from the method signature):
- (void)getMyDataWithCompletion:(void(^)(NSData *data))completion {
MyUIDocument *doc = [[MyUIDocument alloc] initWithFileURL:fileURL];
[doc openWithCompletionHandler:^(BOOL success) {
completion((success ? doc.myResponseData : nil));
}];
}
The same problem exists in swift and you can add a similar completion block:
func getMyData(completion: ((data: NSData?) -> Void) {
data = ...
completion(data)
}
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