Question

我创建了一个使用Facebook登录的功能。

public void Login ()
{
    var ctx = Forms.Context as MainActivity;
    var accounts = 
        new List<Account>(AccountStore.Create (ctx).FindAccountsForService (SERVICE));
    if (accounts.Count == 1) {
        GetAccount (accounts [0]);
        return;
    }

    var auth = new OAuth2Authenticator (
        clientId: FBID,
        scope: string.Empty,
        authorizeUrl: new Uri (AUTH_URL),
        redirectUrl: new Uri (REDIRECT_URL));

    auth.Completed += (sender, eventArgs) => {
        AccountStore.Create (ctx).Save (eventArgs.Account, "Facebook");
        GetAccount (eventArgs.Account);
    };
    ctx.StartActivity (auth.GetUI (ctx));
}

问题是，在FB登录页面输入我的凭据后，在到达Completed事件之前会抛出异常。
我已经从GitHub下载了Xamarin.Auth项目试图调试程序，但遗憾的是它不会在断点处中断。

Caused by: JavaProxyThrowable: System.NullReferenceException: Object reference not set to an instance of an object
at Xamarin.Auth.OAuth2Authenticator.OnRetrievedAccountProperties (System.Collections.Generic.IDictionary`2) [0x00017] in d:\Downloads\Xamarin.Auth-master\Xamarin.Auth-master\src\Xamarin.Auth\OAuth2Authenticator.cs:373
at Xamarin.Auth.OAuth2Authenticator.OnRedirectPageLoaded (System.Uri,System.Collections.Generic.IDictionary`2,System.Collections.Generic.IDictionary`2) [0x00016] in d:\Downloads\Xamarin.Auth-master\Xamarin.Auth-master\src\Xamarin.Auth\OAuth2Authenticator.cs:282
at Xamarin.Auth.WebRedirectAuthenticator.OnPageEncoun...[intentionally cut off]

我现在正在努力解决这个问题。请帮忙！

Answer 1

我找到了！这是一个混合的情况我的调试器没有停在断点处（不知道为什么）造成这个问题的原因是我用Login方法用OnCreate()方法创建了一个Object 然后我将EventHandler附加到该Object的事件 Authenticator从他的Intent回来的那一刻，我的对象绑定的Context已经消失了理解它可能有点模糊，但也许一些代码会进一步澄清。

//Not working, causes the problem
public class MyActivity {
    MyAuthenticator auth; //the object containing Login();
    public void OnCreate() {
        auth=new MyAuthenticator();
        auth.LoggedIn += blabla;
    }
    public void SomeMethod() {
        auth.Login();
    }
}

解决方案：

//Working, own scope
public class MyActivity {
    public void OnCreate() {
        //ILB
    }
    public void SomeMethod() {
        var auth=new MyAuthenticator();
        auth.LoggedIn += blabla;
        auth.Login();
    }
}

Xamarin.Auth OAuth2Authenticator Facebook NullReferenceException

1 个答案: