How to repaint NSTableView immediately after reloadData - objective-c

Question

I have added a NSTableView and set the delegate and datasource correctly.
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
_items = [[NSMutableArray alloc] init];
[_items addObject:#"ready"];
[self.mainTableView reloadData];
}
- (NSInteger)numberOfRowsInTableView:(NSTableView *)tableView {
return [self.items count];
}
- (NSView *)tableView:(NSTableView *)tableView viewForTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row {
NSTableCellView *result = [tableView makeViewWithIdentifier:tableColumn.identifier owner:self];
result.textField.stringValue = [self.items objectAtIndex:row];
return result;
}
There is also a NSButton connected with the following code:
- (IBAction)buttonPressed:(id)sender {
for (int i = 1; i <= 10; i++) {
NSString *item = [NSString stringWithFormat:#"%d", i];
[_items replaceObjectAtIndex:0 withObject:item];
[self.mainTableView reloadData];
[NSThread sleepForTimeInterval:0.2f];
}
}
The program ran correctly and shown "ready" in the table view, but when I clicked the button, the content of the table view didn't change immediately. It changed after 2 second, and just show the last number - 10.
What I want is change the content of NSTableViw from 1 to 10 but not directly get the final number. How can I make it repaint immediately after reloadData?

Answer 1

[NSThread sleepForTimeInterval:0.2f];
You're sleeping the thread and wondering why things seem to be delayed?!
[_items replaceObjectAtIndex:0 withObject:item];
You're replacing every item in the array and wondering why only the last item is displayed?!
You shouldn't be sleeping the main thread at all. Remove that line; sending reloadData will make the table view redisplay itself as soon as possible.
To fill up the array, do this:
for (int i = 1; i <= 10; i++) {
NSString *item = [NSString stringWithFormat:#"%d", i];
[_items addObject:item];
}
[self.mainTableView reloadData];
Notice that I've moved the reloadData outside of the loop. You shouldn't send that until you've finished updating the data and are ready for the table view to redraw.

Answer 2

How can I make it repaint immediately after reloadData?
By returning after reloadData. There is no other way. You cannot cause the table view to redraw while your code is still running. Even if you used another thread, it wouldn't work the way you're envisioning.
If you want to modify the table over time, you can use an NSTimer to modify the data periodically, and then call reloadData (or better yet, reloadRowsAtIndexPaths:withRowAnimation:) after each change.
The user interface will never draw in the middle of your code. You have to return to let it update.
It is not possible for the UI to update while your code runs on the main thread. There are several approaches to providing UI updates during processing:
Do some work, schedule to do some more work with a timer or performSelector:withObject:afterDelay:, return so that the UI can update. This is what I described above.
Break your work into small units and schedule them using an NSOperationQueue or GCD queue. If you run these on the main queue, this is effectively the same as the first option; you're just letting the OS do the scheduling.
Run your processing on a background thread and update the data asynchronously. Periodically update the UI with a timer. This is good for simple progress meters, but it's hard to synchronize if you want the UI updates to be at specific points. This introduces all of the headaches of multi-threaded code, such as locking and atomicy.