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

While a preferred solution requires zero lines of code, if you must trigger a redraw, do so in setNeedsDisplay, which in turn invokes drawRect.
No need to listen to notifications nor refactor the code.

Swift

override func layoutSubviews() {
    super.layoutSubviews()
    self.setNeedsDisplay()
}

Objective-C

- (void)layoutSubviews {
    [super layoutSubviews];
    [self setNeedsDisplay];
}

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Note:
layoutSubviews is a UIView method, not a UIViewController method.