UiAlertView with UIProgressView for copying files locally - ios

Question

I've been trying to get this working for a day now and I'm still failing. I want to copy a number of files into the Documents folder of my app from the bundle when the app is installed, but this makes the user wait for a long time with the app showing the splash screen.
So I thought I'd make an initial UIAlertView with a UIProgressView as a subview that gets updated every time a file is copied into the documents folder. However the alert shows and the progress bar never gets updated. My logic was:
Set up the UIProgressView and UIAlertView as instance variables of my ViewController.
In ViewDidLoad, present the alert and set the delegate
In - (void)didPresentAlertView:(UIAlertView *)alertView perform a for loop that copies the files and updates the UI. the code was :
- (void)didPresentAlertView:(UIAlertView *)alertView{
NSString *src, *path;
src = // path to the Bundle folder where the docs are stored //
NSArray *docs = [[NSFileManager defaultManager]contentsOfDirectoryAtPath:src error:nil];
float total = (float)[docs count];
float index = 1;
for (NSString *filename in docs){
path = [src stringByAppendingPathComponent:filename];
if ([[NSFileManager defaultManager]fileExistsAtPath:path]) {
... // Copy files into documents folder
[self performSelectorOnMainThread:#selector(changeUI:) withObject:[NSNumber numberWithFloat:index/total] waitUntilDone:YES];
index++;
}
}
[alertView dismissWithClickedButtonIndex:-1 animated:YES];
}
And the code for ChangeUI is
- (void) changeUI: (NSNumber*)value{
NSLog(#"change ui %f", value.floatValue);
[progressBar setProgress:value.floatValue];
}
However this just updates the UI from 0 to 1, although the NSLog prints all the intermediate values. Does anyone here know what I'm doing wrong?
Thanks in advance.

Answer 1

The problem is that your loop is on the main thread, and thus the UI has no chance to update until the very end. Try doing the work on a background thread using GCD:
dispatch_async(DISPATCH_QUEUE_PRIORITY_DEFAULT, ^
{
NSString *src, *path;
src = // path to the Bundle folder where the docs are stored //
NSArray *docs = [[NSFileManager defaultManager]contentsOfDirectoryAtPath:src error:nil];
float total = (float)[docs count];
float index = 1;
for (NSString *filename in docs){
path = [src stringByAppendingPathComponent:filename];
if ([[NSFileManager defaultManager]fileExistsAtPath:path]) {
... // Copy files into documents folder
dispatch_async(dispatch_get_main_queue(), ^{ [self changeUI:[NSNumber numberWithFloat:index/total]]; } );
index++;
}
}
dispatch_async(dispatch_get_main_queue(), ^{ [alertView dismissWithClickedButtonIndex:-1 animated:YES]; } );
} );