Android Studio NullPointerException，尝试使用parse.com

Question

我正在尝试将Parse.com用于我的应用程序的用户登录/注册活动，并且通过遵循本教程http://www.androidbegin.com/tutorial/android-parse-com-simple来学习如何使用它。 -login-and-signup-tutorial / 。 但是，在我输入所有内容之后，我的应用程序继续崩溃并给出了NullPointerException

这是我的MainActivity

package com.example.ed.parselogintutorial;

import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

import com.parse.Parse;
import com.parse.ParseAnonymousUtils;
import com.parse.ParseUser;


public class MainActivity extends Activity {

    public void onCreate(Bundle savedInstanceState) {

        // Enable Local Datastore.
        Parse.enableLocalDatastore(this);

        Parse.initialize(this, "T9so2huSfs1xMHwEjx9vSeUuKeyBZsXVyG4QHi7K", "yiQz0RMs9TCkWu8EsdsoVxcPWGlTyAmO20JuEh0X");

        super.onCreate(savedInstanceState);

        //Determine whether the current user is an anonymous user
        if (ParseAnonymousUtils.isLinked(ParseUser.getCurrentUser())) {
            //If user is anonymous, send the user to LoginSignupActivity.class
            Intent intent = new Intent(MainActivity.this,
                    LoginSignupActivity.class);
            startActivity(intent);
            finish();
        } else {
            //If current user is no anonymous user
            //Get current user data from Parse.com
            ParseUser currentUser = ParseUser.getCurrentUser();
            if (currentUser != null) {
                //Send logged in users to Welcome.class
                Intent intent = new Intent(MainActivity.this, Welcome.class);
                startActivity(intent);
                finish();
            } else {
                //Send User to LoginSignupActivity.class
                Intent intent = new Intent(MainActivity.this,
                        LoginSignupActivity.class);
                startActivity(intent);
                finish();
            }
        }
    }


}

这是堆栈

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ed.parselogintutorial/com.example.ed.parselogintutorial.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean com.parse.ParseUser.isLinked(java.lang.String)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
        at android.app.ActivityThread.access$800(ActivityThread.java:151)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5257)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

阿萨

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean com.parse.ParseUser.isLinked(java.lang.String)' on a null object reference
        at com.parse.ParseAnonymousUtils.isLinked(ParseAnonymousUtils.java:51)
        at com.example.ed.parselogintutorial.MainActivity.onCreate(MainActivity.java:28)
        at android.app.Activity.performCreate(Activity.java:5990)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)  
        android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390) 
        at android.app.ActivityThread.access$800(ActivityThread.java:151)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5257)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

很抱歉，如果这里有一个非常明显的错误，因为我是Android开发的新手，请以前使用过Parse.com的人或对此错误有任何了解的人，请教我如何解决它。 先感谢您。

Answer 1

阅读本教程下面的注释，给定的代码存在问题。 以下是其中一项评论的建议：

太早了，所以我不确定他们要在这里做什么...摆脱ParseApplication.java并将其放在您的mainactivity.java中

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main); <<----UNDER THIS (left in for location purpose)

// Add your initialization code here

Parse.initialize(this, "YOUR_APPLICATION_ID", "YOUR_CLIENT_KEY");

ParseUser.enableAutomaticUser();

ParseACL defaultACL = new ParseACL();

// If you would like all objects to be private by default, remove this

// line.

defaultACL.setPublicReadAccess(true);

ParseACL.setDefaultACL(defaultACL, true);

// Determine whether the current user is an anonymous user

if (ParseAnonymousUtils.isLinked(ParseUser.getCurrentUser())) { <<----(left in for location purpose)

本质上，问题在于您没有调用setContentView（R.layout.activity_main）; 在尝试调用Parse函数之前。