Android应用程序Facebook登录：NULL指针异常

Question

My problem is somewhat like these only... First and Second Question. I've tried everything given on these posts but to no relief.

So I am using android-simple-facebook library to create a facebook login. Here's my LoginActivity.java

public class LoginActivity extends Activity {
    private Button mButtonLogin;
    private SimpleFacebook mSimpleFacebook;
    protected static final String TAG = LoginActivity.class.getName();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        mSimpleFacebook = SimpleFacebook.getInstance();
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        mButtonLogin = (Button) findViewById(R.id.button_login);
        setLogin();
    }

    public void setLogin() {

        final OnLoginListener onLoginListener = new OnLoginListener() {
            @Override
            public void onLogin() {
                Log.i(TAG, "Logged in");
            }
        };

        mButtonLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View arg0) {
                mSimpleFacebook.login(onLoginListener);
            }
        });
    }

    @Override
    public void onResume() {
        super.onResume();
       // mSimpleFacebook = SimpleFacebook.getInstance();
    }
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        mSimpleFacebook.onActivityResult(this, requestCode, resultCode, data); 
        super.onActivityResult(requestCode, resultCode, data);
    }


}

But as soon as i click the login button, the app crashes with NullPointerException. Here's the LogCat

09-21 15:54:40.109: E/AndroidRuntime(21895): FATAL EXCEPTION: main
09-21 15:54:40.109: E/AndroidRuntime(21895): Process: www.kb.com, PID: 21895
09-21 15:54:40.109: E/AndroidRuntime(21895): java.lang.NullPointerException
09-21 15:54:40.109: E/AndroidRuntime(21895):    at www.kb.com.LoginActivity$2.onClick(LoginActivity.java:81)
09-21 15:54:40.109: E/AndroidRuntime(21895):    at android.view.View.performClick(View.java:4438)
09-21 15:54:40.109: E/AndroidRuntime(21895):    at android.view.View$PerformClick.run(View.java:18422)
09-21 15:54:40.109: E/AndroidRuntime(21895):    at android.os.Handler.handleCallback(Handler.java:733)
09-21 15:54:40.109: E/AndroidRuntime(21895):    at android.os.Handler.dispatchMessage(Handler.java:95)
09-21 15:54:40.109: E/AndroidRuntime(21895):    at android.os.Looper.loop(Looper.java:136)
09-21 15:54:40.109: E/AndroidRuntime(21895):    at android.app.ActivityThread.main(ActivityThread.java:5001)
09-21 15:54:40.109: E/AndroidRuntime(21895):    at java.lang.reflect.Method.invokeNative(Native Method)
09-21 15:54:40.109: E/AndroidRuntime(21895):    at java.lang.reflect.Method.invoke(Method.java:515)
09-21 15:54:40.109: E/AndroidRuntime(21895):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
09-21 15:54:40.109: E/AndroidRuntime(21895):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
09-21 15:54:40.109: E/AndroidRuntime(21895):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

Please check if you are using the correct API-call. The API documentation states for getInstance()

/**
 * Get the instance of {@link SimpleFacebook}. <br>
 * <br>
 * <b>Important:</b> Use this method only after you initialized this library
 * or by: {@link #initialize(Activity)} or by {@link #getInstance(Activity)}
 * 
 * @return The {@link SimpleFacebook} instance
 */
public static SimpleFacebook getInstance() {
    return mInstance;
}

I did not see a call like initialize(Activity) or getInstance(Activity) in your code snippet.

Answer 2

As it turns out there was nothing wrong with the code or the library, but was an issue with android support lib. I finally found the solution here