How do I get a variable out of a completion block? [duplicate] - ios

Question

This question already has answers here:
Change value of NSString inside block
(2 answers)
Closed 9 years ago.
(void)fetchLastMessageInChannel
{
__weak id weakSelf = self;
for (ANKChannel *channel in self.channelArray)
{
NSLog(#"channels %#",channel);
NSLog(#"channel last message %#",channel.latestMessageID);
[[ClientManager currentClient] fetchMessageWithID:channel.latestMessageID inChannel:channel
completion:^(id responseObject, ANKAPIResponseMeta *meta, NSError *error)
{
NSLog(#"message object %#",responseObject);
ANKMessage *message = responseObject;
dispatch_async(dispatch_get_main_queue(), ^{
[weakSelf populateTextViews:message.text];
});
NSLog(#"message text %#",message.text);
}];
}
}
-(void)populateTextViews:(NSString *)message
{
NSMutableArray *textViews = [#[] mutableCopy];
NSMutableAttributedString *postText = [[NSMutableAttributedString alloc] initWithString:message];
[postText addAttributes:#{
NSFontAttributeName : [UIFont preferredFontForTextStyle:UIFontTextStyleBody],
NSForegroundColorAttributeName : [UIColor darkTextColor]
}
range:NSMakeRange(0, postText.length)];
UITextView *postTextView = [[UITextView alloc] initWithFrame:CGRectMake(80, 30, kPostLabelMaxWidth, 44)];
postTextView.attributedText = postText;
postTextView.dataDetectorTypes = UIDataDetectorTypeAll;
postTextView.backgroundColor = [UIColor whiteColor];
postTextView.editable = NO;
postTextView.scrollEnabled = NO;
postTextView.clipsToBounds = NO; // So it doesn't clip the text selector
CGRect textViewBounds = postTextView.bounds;
textViewBounds.origin = CGPointMake(80, 30);
textViewBounds.size.width = MAX(textViewBounds.size.width, kPostLabelMaxWidth);
textViewBounds.size.height = postTextView.contentSize.height;
postTextView.bounds = textViewBounds;
[postTextView sizeToFit]; // Reload the content size
[textViews addObject:postTextView];
self.channelTextViewArray = [textViews copy];
}
This is where I stand now as far as my methods go with the help I've received. The self.channelTextViewArray is returning nil and causing a crash because the populateTextViews(NSString*)message never gets called.
Any ideas?

Answer 1

If ClientManager call is async, the populateTextViews method will complete before the async call returns, which is why you can't use the value set in its completion block.
Either put...
NSMutableAttributedString *postText = [[NSMutableAttributedString alloc] initWithString:messageText];
...inside the completion block, or call out to a method inside the completion block once you have the messageText. In doing that you will not have to declare the __block variable either.
If there will be a UI update, make sure that happens on the main thread.
EDIT
This the basic idea, but I'm guessing you're updating more than one text view so you may need to change the signatures around. If you get the basic idea -- calling an async method doesn't interrupt the flow of your code (basically it says "do this when you have a chance, possibly on another thread"). That's the reason you have a completion block -- it's a place in your code where you know that the async method you called has completed.
If what's inside the block isn't getting called at all, make sure that self.channelArray has values, and look at what fetchMessageWithID does if something goes wrong.
- (void)populateTextViews
{
__weak id weakSelf = self;
for (ANKChannel *channel in self.channelArray)
{
[[ClientManager currentClient] fetchMessageWithID:channel.latestMessageID inChannel:channel
completion:^(id responseObject, ANKAPIResponseMeta *meta, NSError *error)
{
NSLog(#"message object %#",responseObject);
ANKMessage *message = responseObject;
dispatch_async(dispatch_get_main_queue(), ^{
[weakSelf updateTextView:message.text];
});
}];
}
}
- (void)updateTextView:(NSString *)message
{
// Make an attributed string from the post text content
NSMutableAttributedString *postText = [[NSMutableAttributedString alloc] initWithString:messageText];
self.textView.attributedText = postText;
}