Android错误：无法恢复活动..？

Question

我是Android的新手并尝试添加Facebook登录并在使用Android工作室使用facebook sdk在Android中单击Logout按钮（使用AccessTokenTracker）后捕获事件但是我收到此错误

这是logcat，

// (please horizontal scroll for logcat)
01-12 00:47:15.306 12572-12572/com.example.arpit.facebooklogindemo E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                 java.lang.RuntimeException: Unable to resume activity {com.example.arpit.facebooklogindemo/com.example.arpit.facebooklogindemo.MainActivity}: java.lang.NullPointerException
 at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2790)
 at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2819)
 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2266)
 at android.app.ActivityThread.access$600(ActivityThread.java:141)
 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
 at android.os.Handler.dispatchMessage(Handler.java:99)
 at android.os.Looper.loop(Looper.java:137)
 at android.app.ActivityThread.main(ActivityThread.java:5103)
 at java.lang.reflect.Method.invokeNative(Native Method)
 at java.lang.reflect.Method.invoke(Method.java:525)
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
 at dalvik.system.NativeStart.main(Native Method)
                                                                                  Caused by: java.lang.NullPointerException
 at com.example.arpit.facebooklogindemo.MainActivity.onResume(MainActivity.java:83)
 at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1192)
 at android.app.Activity.performResume(Activity.java:5211)
 at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2780)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2819) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2266) 
at android.app.ActivityThread.access$600(ActivityThread.java:141) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256) 
at android.os.Handler.dispatchMessage(Handler.java:99) 
at android.os.Looper.loop(Looper.java:137) 
at android.app.ActivityThread.main(ActivityThread.java:5103) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:525) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
at dalvik.system.NativeStart.main(Native Method)

这是AndroidManifest.xml，

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.arpit.facebooklogindemo">

    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

         //from http://developers.facebook.com
        <meta-data android:name="com.facebook.sdk.ApplicationId"
            android:value="@string/app_id"/>

        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        //from http://developers.facebook.com
        <activity android:name="com.facebook.FacebookActivity"
            android:configChanges=
                "keyboard|keyboardHidden|screenLayout|screenSize|orientation"
            android:theme="@android:style/Theme.Translucent.NoTitleBar"
            android:label="@string/app_name" />

    </application>

</manifest>

这是activity_main.xml，

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.arpit.facebooklogindemo.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        android:id="@+id/textView2" />

     //from http://developers.facebook.com
    <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_centerVertical="true"
        android:layout_centerHorizontal="true" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Large Text"
        android:id="@+id/textView"
        android:layout_above="@+id/login_button"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="90dp" />

</RelativeLayout>

这是MainActivity.java，

package com.example.arpit.facebooklogindemo;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
import android.widget.Toast;

import com.facebook.AccessToken;
import com.facebook.AccessTokenTracker;
import com.facebook.CallbackManager;
import com.facebook.FacebookCallback;
import com.facebook.FacebookException;
import com.facebook.FacebookSdk;
import com.facebook.Profile;
import com.facebook.login.LoginResult;
import com.facebook.login.widget.LoginButton;

public class MainActivity extends AppCompatActivity {

    CallbackManager callbackManager;
    LoginButton loginButton;
    TextView textView;
    AccessTokenTracker accessTokenTracker;

    private FacebookCallback<LoginResult> mFacebookCallback = new FacebookCallback<LoginResult>() {
        @Override
        public void onSuccess(LoginResult loginResult) {
            Profile profile = Profile.getCurrentProfile();
            if(profile != null){
                fillTextView(profile);
            }
        }

        @Override
        public void onCancel() {

        }

        @Override
        public void onError(FacebookException error) {
            Log.d("find", String.valueOf(error));
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        FacebookSdk.sdkInitialize(getApplicationContext());
        setContentView(R.layout.activity_main);
        textView = (TextView)findViewById(R.id.textView);

        callbackManager = CallbackManager.Factory.create();

        accessTokenTracker = new AccessTokenTracker() {
            @Override
            protected void onCurrentAccessTokenChanged(AccessToken oldAccessToken, AccessToken currentAccessToken) {
                if(currentAccessToken == null){
                    textView.setText("Logged out");
                }
            }
        };
        accessTokenTracker.startTracking();

        loginButton = (LoginButton)findViewById(R.id.login_button);

        loginButton.registerCallback(callbackManager, mFacebookCallback);

    }

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

    @Override
    protected void onResume(){
        super.onResume();
        Profile profile = Profile.getCurrentProfile();
        textView.setText(profile.getName());
    }

    @Override
    protected void onDestroy(){
        super.onDestroy();
        accessTokenTracker.stopTracking();
    }

    private void fillTextView(Profile profile){
        textView.setText(profile.getName());
    }
}

Answer 1

查看日志中的这一行：

Caused by: java.lang.NullPointerException
at com.example.arpit.facebooklogindemo.MainActivity.onResume(MainActivity.java:83)

很明显，由于onResume()函数中的NullPointerException ，您的应用程序崩溃了。 一个可能的原因是您在调用profile.getName()时可能会获得空配置文件详细信息

在设置文本之前进行空检查，如下所示：

Profile profile = Profile.getCurrentProfile();
if(null != profile)
        textView.setText(profile.getName());

有时，您可能会获得null或旧的配置文件详细信息。 在这种情况下，您需要请求更新的个人资料详细信息。 以下是samle代码：

 Profile profile = Profile.getCurrentProfile();
    if(null != profile) {
          new ProfileTracker() {
                                @Override
                                protected void onCurrentProfileChanged(Profile oldProfile, Profile currentProfile) {
                                    if (currentProfile != null) {
                                        // handle it
                                        stopTracking();
                                    }
                                }
                            }.startTracking();
    } else {
            textView.setText(profile.getName());
}

Answer 2

在设置textView之前对onResume进行空检查。