redraw a custom uiview when changing a device orientation

Question

1. If I draw my chart inside - (void)drawRect:(CGRect)rect is just enough to set [_chartView setContentMode:UIViewContentModeRedraw] and this method will be called when device changes it's orienatation and it's possible to calculate f.e. new center point for my chart.
2. If I create a view like a subview using - (id)initWithFrame:(CGRect)frame and then add it in view controller like [self.view addSubview:chartView];. How in this case I can handle rotation to redraw my chart?

Answer 1

Zero Lines of Code

Use .redraw

Programmatically invoking myView.contentMode = .redraw when creating the custom view should suffice. It is a single flag in IB and, as such, the 0 lines of code prefered way. See Stack Overflow How to trigger drawRect on UIView subclass.

Answer 2

To make your chart rendered correctly when device orientation changes you need to update chart's layout, here is the code that you should add to your view controller:

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];

    _chartView.frame = self.view.bounds;
    [_chartView strokeChart];
}