Question

I have a read-only text field that I use as a log display. I have a operation that removes all the files in app’s document directory. I want to insert a line of log when I remove each file. But the text field is only updated when the whole operation got finished. How do I fix this?

Here is my code:

NSFileManager *fm = [[[NSFileManager alloc] init] autorelease];
NSError *error = nil;
for (NSString *fileName in array) {
    NSString *filePath = [DOCUMENT_PATH_VALUE stringByAppendingFormat:@"/%@", fileName];
    [fm removeItemAtPath:filePath error:&error];

    if (!error) {
        NSString *log = [NSString stringWithFormat:@"removed success: %@", fileName];
        [self logThis:log];
    }else{
        NSString *log = [NSString stringWithFormat:@"remove failed: %@, %@", fileName, [error localizedDescription] ];
        [self logThis:log];

---

-(void)logThis:(NSString*) text{
    NSRange range = NSMakeRange([updateLogTextView.text length], [text length]);
    updateLogTextView.text = [updateLogTextView.text stringByAppendingFormat:@"%@\n", text]; 

    [updateLogTextView scrollRangeToVisible:range];
}

Answer 1

You need to move your long-running operation into a background thread/queue and make sure that your UI-updating code is always executed on the main thread.

Example:

- (void)processFiles:(NSArray *)array
{
    //You need to create your own autorelease pool in background threads:
    NSAutoreleasePool *pool = [NSAutoreleasePool new];
    //...
    NSString *log = ...;
    [self performSelectorOnMainThread:@selector(logThis:) withObject:log waitUntilDone:NO];
    //...
    [pool release];
}

You would then start your operation using:

[self performSelectorInBackground:@selector(processFiles:) withObject:files];

Using Grand Central Dispatch with blocks would be another option.

Refer to the Threading Programming Guide and the Concurrency Programming Guide for more in-depth information.