display UIView with UIActivityIndicatorView when it takes a long time to do something

I have some codes to process a large size file, it will take a long time. I hop开发者_Python百科e to display a view with UIActivityIndicatorView when the progress starts and hide the view when it completed

The code as below

[[NSNotificationCenter defaultCenter] postNotificationName:@"DisplayProcessing" object:nil];

[self dosomething];//take a long time                   

[[NSNotificationCenter defaultCenter] postNotificationName:@"HideProcessing" object:nil];

but its excution order is:

[[NSNotificationCenter defaultCenter] postNotificationName:@"DisplayProcessing" object:nil];

[[NSNotificationCenter defaultCenter] postNotificationName:@"HideProcessing" object:nil];

[self dosomething];//take a long time       

so there is nothing display

Welcome any comment

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why dont you use thread? start your indicator in method dosomething and then stop that indicator

start indicator in main method and replace

[self dosomething];

with

[self performSelectorOnMainThread:@selector(dosomething:) withObject:nil waitUntilDone:NO];

and stop your activity here