- (void)displayLayer:(CALayer *)layer {
    if (_curFrame) {
        layer.contents = (__bridge id)_curFrame.CGImage;
    } else {
        // If we have no animation frames, call super implementation. iOS 14+ UIImageView use this delegate method for rendering.
        if ([UIImageView instancesRespondToSelector:@selector(displayLayer:)]) {
            [super displayLayer:layer];
        }
    }
}

+ (void)load
{
    Method a = class_getInstanceMethod(self, @selector(displayLayer:));
    Method b = class_getInstanceMethod(self, @selector(swizzing_displayLayer:));
    method_exchangeImplementations(a, b);
}

- (void)swizzing_displayLayer:(CALayer *)layer
{   
    //通过变量名称获取类中的实例成员变量
    Ivar ivar = class_getInstanceVariable(self.class, "_curFrame");
    UIImage *_curFrame = object_getIvar(self, ivar);

    if (_curFrame) {
        layer.contents = (__bridge id)_curFrame.CGImage;
    } else {
        if (@available(iOS 14.0, *)) {
            [super displayLayer:layer];
        }
    }
}