我正在使用Mondroid示例进行Facebook SDK java绑定（https://developers.facebook.com/docs/tutorials/androidsdk/3.0/scrumptious/authenticate/）。我将facebook绑定添加到我的项目中，并尝试按照facebook sdk说明设置基于会话的登录活动。
注意：Xamarin网站上提供的xamarin facebook绑定不完整。它没有遵循Facebook身份验证示例所需的类。我假设它仍然使用SDK的V2。
当初始化Com.Faccebook.UiLifecycleHelper时，我收到一条错误，上面写着“参数applicationId不能为空”
导致问题的代码是我初始化Facebook UILifecyleHelper时。 FBCallback是我的类，它实现了facebook StatusCallback接口：
uiHelper = new UiLifecycleHelper (this, new FBCallback (this));
uiHelper.OnCreate (bundle);
我尝试添加：
<meta-data android:name="com.facebook.sdk.ApplicationId" android:value="@string/app_id" />
到AndroidManifest.xml，以及以下到Strings.xml：
<string name="app_id">12471902489108</string>
但仍然无法读取应用程序ID。
我为“com.facebook.sdk.ApplicationId”尝试了10种不同的大小写，但我仍然遇到同样的错误。
以下是异常的堆栈跟踪：
Java.Lang.NullPointerException: Argument applicationId cannot be null
at Android.Runtime.JNIEnv.CallVoidMethod (intptr,intptr,Android.Runtime.JValue[ [0x00023] in /Users/builder/data/lanes/monodroid-mlion-master/294d4619/source/monodroid/src/Mono.Android/src/Runtime/JNIEnv.g.cs:368
at Com.Facebook.UiLifecycleHelper.OnCreate (Android.OS.Bundle) [0x00048] in c:\buddyup\monodroid-samples\monodroid-samples\Facebook\Mono.Facebook\obj\Debug\generated\src\Com.Facebook.UiLifecycleHelper.cs:158
at BuddyUp.FBLoginActivity.OnCreate (Android.OS.Bundle) [0x00027] in c:\buddyup\mobile\buddyup_mobile\BuddyUp\FBLoginActivity.cs:71
at Android.App.Activity.n_OnCreate_Landroid_os_Bundle_ (intptr,intptr,intptr) [0x00010] in /Users/builder/data/lanes/monodroid-mlion-master/294d4619/source/monodroid/src/Mono.Android/platforms/android-10/src/generated/Android.App.Activity.cs:1561
at (wrapper dynamic-method) object.0f7bec40-34dd-40a5-a892-0a3ffbf275a4 (intptr,intptr,intptr) <IL 0x00017, 0x00043>
--- End of managed exception stack trace ---
java.lang.NullPointerException: Argument applicationId cannot be null
at com.facebook.internal.Validate.notNull(Validate.java:29)
at com.facebook.Session.<init>(Session.java:224)
at com.facebook.Session.<init>(Session.java:209)
at com.facebook.UiLifecycleHelper.onCreate(UiLifecycleHelper.java:73)
at buddyup.FBLoginActivity.n_onCreate(Native Method)
at buddyup.FBLoginActivity.onCreate(FBLoginActivity.java:33)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
at android.app.ActivityThread.access$1500(ActivityThread.java:117)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:130)
at android.app.ActivityThread.main(ActivityThread.java:3683)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
at dalvik.system.NativeStart.main(Native Method)