Question

我正在尝试将Facebook登录添加到我的Android应用程序中。当我首先启动应用程序时，它会毫无问题地登录，但之后，无论何时我尝试登录，应用程序都会崩溃。

MainActivity.java如下：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    FacebookSdk.sdkInitialize(this.getApplicationContext());
    setContentView(R.layout.activity_main);
    callbackManager = CallbackManager.Factory.create();
    loginButton = (LoginButton) findViewById(R.id.login_button);
    List<String> permissionNeeds = Arrays.asList("public_profile", "user_friends");
    loginButton.setReadPermissions(permissionNeeds);

    try {
        PackageInfo info = getPackageManager().getPackageInfo("com.example.ryans_000.facebooklogin", PackageManager.GET_SIGNATURES);
        for (Signature signature : info.signatures) {
            MessageDigest md = MessageDigest.getInstance("SHA");
            md.update(signature.toByteArray());
            Log.d("KeyHash:", Base64.encodeToString(md.digest(), Base64.DEFAULT));
        }

    } catch (PackageManager.NameNotFoundException e) {

    } catch (NoSuchAlgorithmException e) {

    }

    loginButton.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {


        @Override
        public void onSuccess(LoginResult loginResult) {
            System.out.println("onSuccess");
        }

        @Override
        public void onCancel() {
            System.out.println("onCancel");
        }

        @Override
        public void onError(FacebookException exception) {
            Log.v("LoginActivity", exception.getCause().toString()); }
    });
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data)
{
    super.onActivityResult(requestCode, resultCode, data);
    callbackManager.onActivityResult(requestCode, resultCode, data);
}}

content_main包含按钮的以下代码：

<com.facebook.login.widget.LoginButton
    android:id="@+id/login_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal"
    android:layout_marginTop="30dp"
    android:layout_marginBottom="30dp" />

Logcat显示以下内容：

02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime: FATAL EXCEPTION: main
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime: Process: com.example.ryans_000.facebooklogin, PID: 23263
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime: java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=64206, result=-1, data=Intent { (has extras) }} to activity {com.example.ryans_000.facebooklogin/com.example.ryans_000.facebooklogin.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Throwable.toString()' on a null object reference
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.app.ActivityThread.deliverResults(ActivityThread.java:3988)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.app.ActivityThread.handleSendResult(ActivityThread.java:4038)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.app.ActivityThread.access$1400(ActivityThread.java:150)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1443)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:168)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5845)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:797)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:687)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Throwable.toString()' on a null object reference
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at com.example.ryans_000.facebooklogin.MainActivity$1.onError(MainActivity.java:92)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at com.facebook.login.LoginManager.finishLogin(LoginManager.java:579)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at com.facebook.login.LoginManager.onActivityResult(LoginManager.java:216)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at com.facebook.login.LoginManager$1.onActivityResult(LoginManager.java:159)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at com.facebook.internal.CallbackManagerImpl.onActivityResult(CallbackManagerImpl.java:82)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at com.example.ryans_000.facebooklogin.MainActivity.onActivityResult(MainActivity.java:100)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.app.Activity.dispatchActivityResult(Activity.java:6439)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.app.ActivityThread.deliverResults(ActivityThread.java:3984)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.app.ActivityThread.handleSendResult(ActivityThread.java:4038) 
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.app.ActivityThread.access$1400(ActivityThread.java:150) 
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1443) 
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102) 
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:168) 
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5845) 
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method) 
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:797)
02-29 09:34:45.306 23263-23263/com.example.ryans_000.facebooklogin E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:687)

Answer 1

我想你的

    @Override
    public void onError(FacebookException exception) {
        Log.v("LoginActivity", exception.getCause().toString()); }

exception.getCause为null因此尝试将其转换为字符串显示空指针异常。尝试修复它。

Answer 2

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Throwable.toString()' on a null object reference

最有可能的是，它指出使用onString（）方法的行在onError（）中，所以尝试改变它。祝你好运！

单击时，Facebook登录按钮会崩溃应用程序

2 个答案: