Help With NSNotifcation and Asynchronous Downloading

问题

I am sending a notification from one view to another view. My problem is that the notification in the view that I am calling in my cellForRowAtIndexPath method is only getting sent when the tableview is scrolling. How can I stop this and make it send the notification once the images have downloaded? Here is my code: https://gist.github.com/756302

Thanks

MKDev

回答1:

as far as I understand your code, the message will trigger the reload of the whole table. That should lead to a refresh of the cells.

Thus, you'll need to check in line 76, if the cell is being drawn because a reload was triggered from the finish-message (and the image is now ready to display) or if you need to start the asynchronous download of the image.

The first thing which comes into my mind to check this is to set a property in reloadTableView:

- (void)reloadTableView
{
    [[NSUserDefaults standardUserDefaults] setBool:YES forKey:@"aaa"];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:@"name" object:nil];
    NSLog(@"removeobserver");
    loadImageFinished = YES;
    // if your table has several sections you'll need to adopt the section number 
    NSIndexSet *indices = [[NSIndexSet alloc] initWithIndex:0];
    [self.tableView reloadSections:indices withRowAnimation:UITableViewRowAnimationFade];
    [indices release];
}

and then to add in

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
   ...
   if (loadImageFinished) {
      ... 
   } else {
      [asyncImage loadImageFromURL:[NSURL URLWithString:pathImage]];
   }
   ...
}

Note that there could be other reasons why the table is being reloaded - the view could have been disappeared or unloaded and you might not wish to trigger your asynnchronous loading several times.

回答2:

Your code should work right, when the connectionDidFinishLoading, you call the NSNotificationCenter to send the notification, there is no post method in cellForRowAtIndexPath

来源：https://stackoverflow.com/questions/4540383/help-with-nsnotifcation-and-asynchronous-downloading