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iOS - How to know when NSOperationQueue finish processing a few operations?

2014-11-02 18:02 471 查看

转自：http://stackoverflow.com/questions/9998532/ios-how-to-know-when-nsoperationqueue-finish-processing-a-few-operations

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I need in my application to download directories and their content. So I decided to implement a NSOperationQueue and I subclassed NSOperation to implement NSURLRequest etc...

The problem is I add all the operations at once and I can't figure out when all the files for one directory are downloaded in order to update the UI and enable this specific directory.

Now I have to wait that all the files from all the directories are downloaded in order to update the UI.

I already implemented key-value observing for the operationCount of the NSOperationQueue and the isFinished of the NSOperation but I don't know when a directory has all the files in it !

Do you have any idea ?

Thanks a lot

iphone ios ipad download nsoperation

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asked Apr 3 '12 at 17:42

Dabrut

472720

It is more convenient to use dispatch_group_async. See this link [link][1] [1]:stackoverflow.com/questions/9632235/… – Igor
Fedorchuk Mar
18 at 8:43

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4 Answers

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Add a "Done"

NSOperation

which
has all other

NSOperations

for
one directory as dependency.

Something like this:

NSInvocationOperation *doneOp = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(done:) object:nil];

NSInvocationOperation *op1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(doSomething:) object:nil];
[queue addOperation:op1];
[doneOp addDependency:op1];

NSInvocationOperation *op2 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(doSomething:) object:nil];
[queue addOperation:op2];
[doneOp addDependency:op2];

NSInvocationOperation *op3 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(doSomething:) object:nil];
[queue addOperation:op3];
[doneOp addDependency:op3];

[queue addOperation:doneOp];

doneOp

will
only run after

op1

op2

and

op3

have
finished executing.

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edited Apr
5 '12 at 5:24

Costique

16.4k24562

answered Apr 3 '12 at 20:02

Matthias Bauch

54.8k5122166

I forgot to mention that my operations are concurrent. Is your example still ok ? – Dabrut Apr
3 '12 at 21:37

Of course, that's the whole point of dependencies. In a non-concurrent operation queue you would just add your operations in the correct
order to achieve the same. But an operation will not run until all its dependencies have finished executing. – Matthias
Bauch Apr
4 '12 at 10:08

Kudos to you. That's exactly what I was looking for ! – Dabrut Apr
4 '12 at 20:14

Quite an elegant solution! – Costique Apr
5 '12 at 5:25

Many thanks for your answer help me – wod Jan
21 '13 at 7:12

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[opQueue operationCount]

Hope this helps

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answered Feb 5 '13 at 11:39

Radix

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One approach would be to create some sort of Directory class with a properties such as loadedCount (initially 0) and fileCount (initialized to however many files are in the directory) and create a dictionary mapping each NSOperation to the appropriate Directory
before adding the operation to the queue. Inside your callback for isFinished, you could pull the Directory object for the given NSOperation out of the dictionary and increment the directory.loadedCount by 1. If your directory.loadedCount == directory.fileCount,
trigger an update to the UI.

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answered Apr 3 '12 at 18:56

tronbabylove

80148

That was my first idea. But I was wondering if that was the correct way to do it or if there was a better way to do it. – Dabrut Apr
3 '12 at 19:08

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You can refactor your code to avoid enqueuing all requests at once. Enqueue only requests for a single directory at a time. When

operationCount

reaches
zero, you can be sure that all the requests either completed or failed, update the UI and enqueue the requests for the next directory. Proceed until the array of directories is empty.

The advantages are:

relative simplicity

you don't have to query the file system only to figure out what has been downloaded

if need be, you can re-enqueue failed requests without changing other logic.

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answered Apr 3 '12 at 19:56

Costique

16.4k24562

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