用于零值颤振的颤振零值检查运算符

Question

我正在尝试检查用户是否付款。如果付款完成，用户将看到主页。如果未付款，用户将看到付款页面。问题是，我在null值上使用了null检查运算符。我做错了什么？

class TwoPage extends StatelessWidget {
Package? offer;
PurchaserInfo? _purchaserInfo;
bool? payment;

Future<bool> ispaymentdone() async {
await Purchases.setDebugLogsEnabled(true);
await Purchases.setup("public_key");
PurchaserInfo purchaserInfo = await Purchases.getPurchaserInfo();
print(purchaserInfo);
print("buraya kadar iyi");
Offerings offerings = await Purchases.getOfferings();
print(offerings);
// optional error handling
// If the widget was removed from the tree while the asynchronous platform
// message was in flight, we want to discard the reply rather than calling
// setState to update our non-existent appearance.
//if (!mounted) return;
_purchaserInfo = purchaserInfo;

if(purchaserInfo.entitlements.all["content-usage"]!=null){
if ( purchaserInfo.entitlements.all["content-usage"]!.isActive) {
print("trueee");
return true;
}
}
return false;
}
@override
Widget build(BuildContext context) {
return FutureBuilder(
future: ispaymentdone(),
builder: (context, snapshot) {
if (snapshot.data == null)
return SizedBox(
child: Center(child: CircularProgressIndicator(color:Colors.purple)),
height: 10.0,
width: 10.0,
);
else if (snapshot.data == true)
return NewHomeScreen();
else
return MainPayment(purchaserInfo: _purchaserInfo, offer: offer);
},
);
}
}

Answer 1

这是因为你对变量使用了null检查运算符，但在你想使用它的时候，特定变量的值是null，你必须给该变量一些初始值，或者确保值不是null。

Answer 2

这是我的错误：

return MainPayment(purchaserInfo: _purchaserInfo, offer: offer);

我没有分配任何变量。