UISwitch在以编程方式更改时不发送valueChanged事件

我有一对通过valueChanged事件连接到IBAction的UISwitch。触摸开关时，valueChanged事件正常触发。但是，如果我以编程方式更改其中一个开关，则不会调用我的IBAction。

I have a pair of UISwitches hooked up to a IBAction via the valueChanged event. The valueChanged event is firing fine when the switches are touched. However, if I change one of the switches programmatically it doesn't call my IBAction.

- (IBAction)switchChanged:(UISwitch *)sender {
    if (sender == self.shippingSwitch) {
        if (self.shippingSwitch.on && !self.PayPalSwitch.on) {
            [self.PayPalSwitch setOn:YES animated:YES];
        }
    }

    if (sender == self.PayPalSwitch) {
        if (!self.PayPalSwitch.on) {
            // This is not working when the PayPal switch is set via the code above
            self.PayPalEmailField.backgroundColor = [UIColor grayColor];
            self.PayPalEmailField.enabled = NO;

            if (self.shippingSwitch.on) {
                [self.shippingSwitch setOn:NO animated:YES];
            }
        } else {
            self.PayPalEmailField.backgroundColor = [UIColor clearColor];
            self.PayPalEmailField.enabled = YES;
        }
    }
}