添加全局监听

添加全局的监听，在发生购买、续期订阅、恢复购买之后全局监听都会被调用。开发者应该在初始化之后尽早的设置监听，以便及时的监听回调

Java

///Adding a listener
UserOrderManager.getProvider().addPurchaseObserver(new OrderObserver() {
    @Override
    public void onUpdateOrders(List<MTGPurchase> purchases) {
        // Monitor order changes
    }
});
///Remove listener
UserOrderManager.getProvider().removePurchaseObserver(orderObserver);

Kotlin

///Adding a listener
UserOrderManager.getProvider().addPurchaseObserver {
    //Monitoring order changes
} 
///Remove listener
UserOrderManager.getProvider().removePurchaseObserver(orderObserver)

Objective-C

///Adding a listener
[AWPurchaseKit addPurchaseObserver:AWPurchaseObserver];
///Remove listener
[AWPurchaseKit removePurchaseObserver:self];

Swift

///Adding a listener
AWPurchaseKit.add(AWPurchaseObserver)
///Remove listener
AWPurchaseKit.remove(AWPurchaseObserver)