tableview静态单元格动态页脚

Question

I have a static cell with 2 sections. One section has 2 rows and the other has a single row. One of the cells in the first section perform an operation that could take up to a minute (decrypting lots of data from the database then encrypting it again.

In order to inform the user that the operation is ongoing and not stuck, I am trying to do the following: (The below is a pseudo of my actual code)

Issue:

the footerString in doStuff is not shown. However the one in callDoStuff is shown just fine... Any ideas what am I doing wrong?

- (void) doStuff
{
    for (int i=0; i<[resultsArray count]; i++)
    {
      rec1 = [decrypt record1];
      footerString = [@"Preparing item : " stringByAppendingString:rec1];
      [self.tableView reload];
      rec2 = [decrypt record2];
      ...
      ...
      ...
      rec10 = [decrypt record10];
    }
}

doStuff is called from another function

- (void) callDoStuff
{
    [self doStuff];
    footerString = @"Done preparing items";
    [self.tableView reload];
}

I do have the following in my tableviewcontroller

- (NSString *)tableView:(UITableView *)tableView titleForFooterInSection:(NSInteger)section
{
    if (section == 0)
        return footerString;
    else
        return @"";
}

Answer 1

You should make your calculation in a background thread. Here you assign a new value to your UILabel, but the main thread has no time to refresh the view.

- (void) callDoStuff
{
    [self doStuff];
}

- (void)doStuff {
    dispatch_async(dispatch_queue_create("myqueue", NULL) , ^(void) {
        // Here you enter in another thread
        for (int i=0; i<[resultsArray count]; i++)
        {
            rec1 = [decrypt record1];
            dispatch_async( dispatch_get_main_queue(), ^{
                // Here you send message to your UILabel in your main thread
                footerString = [@"Preparing item : " stringByAppendingString:rec1];
            });
            [self.tableView reload];
            rec2 = [decrypt record2];
            ...
            rec10 = [decrypt record10];
        }   
        dispatch_async( dispatch_get_main_queue(), ^{
            // Here you send a callback
            [self doOtherStuffAfterDoStuff];
        });
    });    
}

- (void)doOtherStuffAfterDoStuff {
    footerString = @"Done preparing items";
    [self.tableView reload];
}

Then your UI should finely update while your devrypting stuff is ongoing.