How update a label periodically on iOS (every second)? [duplicate]

Question

I use a NSTimer which fires every second and updates a label which displays the remaining time until an event.

I works fine so far. The problem is while I am scrolling the TableView my Label does not update, because the MainThread is blocked by the touch/scroll event.

I thought about creating a second thread for the Timer but I couldn't update the label from a background thread anyways. I had to queue it with performSelector... on the MainThread where it would stuck like before.

Is there any way to update the label while scrolling?

Answer 1

The problem is that a scheduledTimer will not get called while the main thread is tracking touches. You need to schedule the timer in the main run loop.

So instead of doing

[NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(updateLabel:) userInfo:nil repeats:YES];

use

NSTimer* timer = [NSTimer timerWithTimeInterval:1.0f target:self selector:@selector(updateLabel:) userInfo:nil repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];