我是C＃的新手，很抱歉，如果你们中的一些人看起来很容易：）
"Although PayPal usually processes IPN messages immediately, IPN is not synchronized with actions on your website. Internet connectivity is not always 100% reliable and IPN messages can be lost or delayed. The IPN service automatically resends messages until the listener acknowledges them. The service resends messages for up to 4 days.
Because IPN is not a real-time service, your checkout flow should not wait for the IPN message before it is allowed to complete. If the checkout flow is dependent on receiving an IPN message, processing can be delayed by system load or other reasons. You should configure your checkout flow to handle a possible delay."
单击按钮时如何在两种方法之间切换？
单击方法＃1
第二次点击将用于方法＃2
第三次点击将用于方法＃1
等。