setNeedsDisplay在UIImageView的子类上不起作用

Question

import UIKit
class CustomView: UIView {
    override func drawRect(rect: CGRect) {
        print("Draw")
    }
}

Drag a UIView, set its class to be CustomView , create a reference customView to it.

When I call customView.setNeedsDisplay() , drawRect of CustomView get called.

import UIKit
class CustomImageView: UIImageView {
    override func drawRect(rect: CGRect) {
        print("DrawImage")
    }
}

Drag a UIImageView, set its class to be CustomImageView , create a reference customImageView to it.

When I call customImageView.setNeedsdisplay() , nothing happen. Why?

Answer 1

The UIImageView class is optimized to draw its images to the display. UIImageView does not call the drawRect: method of its subclasses. If your subclass needs to include custom drawing code, you should subclass the UIView class instead.