UIScreenEdgePanGestureRecognizer in Objective-C - ios

Question

I am learning objective-c and do not know what this code does. I understand what UIScreenEdgePanGestureRecognizer does. However, I am confused as to what this code is doing with the UIScreenEdgePanGesture.
UIScreenEdgePanGestureRecognizer *rightRecog =
[[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:self action:#selector(resetChart:)];
[rightRecog setEdges:UIRectEdgeRight];
[rightRecog setCancelsTouchesInView:YES];
[self.chartView addGestureRecognizer:rightRecog];
UIScreenEdgePanGestureRecognizer *leftRecog = [[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:self action:#selector(resetChart:)];
[leftRecog setEdges:UIRectEdgeLeft];
[leftRecog setCancelsTouchesInView:YES];
[self.chartView addGestureRecognizer:leftRecog];

Answer 1

This is a code pattern used to define a UIPanGestureRecognizer that checks for finger/pen touches on the devices screen edges from right inside and from left inside the screen center but will cancel any touch event happening inside the view the same time.
The recognizer binds to self.chartView to observe those gestures.
It also defines a method #selector(resetChart:) that will act (action) in case the fingers are sliding in on one side of the chartView. But the method -resetChart: will be part of the ViewController Class or View Class you defined the recogniser inside defined as (self).
UIScreenEdgePanGestureRecognizer *rightRecog =
[[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:self action:#selector(resetChart:)];
[rightRecog setEdges:UIRectEdgeRight];
[rightRecog setCancelsTouchesInView:YES];
[self.chartView addGestureRecognizer:rightRecog];
the above code is setting up the recognizer from the right side.
The code below does the same thing for the left side but will trigger the same method.
UIScreenEdgePanGestureRecognizer *leftRecog = [[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:self action:#selector(resetChart:)];
[leftRecog setEdges:UIRectEdgeLeft];
[leftRecog setCancelsTouchesInView:YES];
[self.chartView addGestureRecognizer:leftRecog];
so it could be melt together like so..
UIScreenEdgePanGestureRecognizer *rightLeftRecog =
[[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:self action:#selector(resetChart:)];
[rightLeftRecog setEdges:UIRectEdgeRight|UIRectEdgeLeft];
[rightLeftRecog setCancelsTouchesInView:YES];
[self.chartView addGestureRecognizer:rightLeftRecog];
because -resetChart: is just doing the same.
which will look like
-(void)resetChart:(UIScreenEdgePanGestureRecognizer*)gesture {
//do some stuff with the gesture or amount of fingers used.
}