Question

如果有人能帮忙解决这个问题会很棒！

我一直得到一个空指针错误，这是奇怪的，因为应用程序在几分钟前工作正常，我看不出有什么问题，它在启动时崩溃了。如果您还需要其他任何有用的信息，请告知我们，以下是所有细节：

logcat的：

04-08 23:31:27.579    5906-5906/com.yupo.dominic.yupo E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.yupo.dominic.yupo/com.yupo.dominic.yupo.LectureLogged}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
        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.yupo.dominic.yupo.MenuFragment1.onCreateView(MenuFragment1.java:49)
        at android.support.v4.app.Fragment.performCreateView(Fragment.java:1786)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1126)
        at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1489)
        at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:548)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
        at android.app.Activity.performStart(Activity.java:5143)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
        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)

清单文件（如果它有用）：

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

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.RECORD_AUDIO" />
<uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS" />
<uses-permission android:name="android.permission.READ_PHONE_STATE" />

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

    <activity
        android:name=".UserAuth"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name=".Login"
        android:label="@string/title_login_area">
    </activity>
    <activity
        android:name=".StudentLogged"
        android:label="@string/title_student_area">
    </activity>
    <activity
        android:name=".Register"
        android:label="@string/register">
    </activity>
    <activity
        android:name=".LectureLogged"
        android:label="@string/title_lecture_area">
    </activity>
    <activity android:name=".MessagingActivity"
        android:screenOrientation="portrait">
    </activity>
    <service android:name=".MessageService">

    </service>
</application>

MenuFragment1类：

package com.yupo.dominic.yupo;

import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

import com.parse.ParseObject;
import com.parse.ParseQuery;
import com.parse.ParseQueryAdapter;
import com.parse.ParseUser;

/**
 * Created by Dominic on 03/03/2015.
 */
public class MenuFragment1 extends Fragment implements View.OnClickListener{

    View rootview;
    Spinner uniSpinner;
    Button changeUniButton;
    String uniSpinnerText;
    ParseUser currentUser;
    ParseQueryAdapter<ParseObject> adapter;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        currentUser = ParseUser.getCurrentUser();

        if(currentUser.getString("type").equalsIgnoreCase("Lecturer"))
        {
            rootview = inflater.inflate(R.layout.menu1_lecture, container, false);

            TextView lectureUniTextView = (TextView) rootview.findViewById(R.id.lectureUniTextView);
            TextView lectureChangeUniTextView = (TextView) rootview.findViewById(R.id.lectureChangeUniTextView);
            uniSpinner = (Spinner) rootview.findViewById(R.id.uniSpinner);
            uniSpinnerSetup();
            changeUniButton = (Button) rootview.findViewById(R.id.changeUniButton);
            changeUniButton.setOnClickListener(this);

            if(currentUser.getString("university").equals(""))
            {
                lectureUniTextView.setText("You do not have a University set!");
                lectureChangeUniTextView.setText("Select a University");
                changeUniButton.setText("Set");

            }
            else
            {
                lectureUniTextView.setText("Your current University is: " + currentUser.getString("university"));
                lectureChangeUniTextView.setText("Change University to");
                changeUniButton.setText("Change");
            }
        }
        else
        {
            rootview = inflater.inflate(R.layout.menu1_student, container, false);

            TextView studentUniTextView = (TextView) rootview.findViewById(R.id.studentUniTextView);
            TextView studentChangeUniTextView = (TextView) rootview.findViewById(R.id.studentChangeUniTextView);
            uniSpinner = (Spinner) rootview.findViewById(R.id.uniSpinner);
            uniSpinnerSetup();
            changeUniButton = (Button) rootview.findViewById(R.id.changeUniButton);
            changeUniButton.setOnClickListener(this);

            if(currentUser.getString("university").equals(""))
            {
                studentUniTextView.setText("You do not have a University set!");
                studentChangeUniTextView.setText("Select a University");
                changeUniButton.setText("Set");

            }
            else
            {
                studentUniTextView.setText("Your current University is: " + currentUser.getString("university"));
                studentChangeUniTextView.setText("Change University to");
                changeUniButton.setText("Change");
            }
        }

        return rootview;
    }

    public void uniSpinnerSetup()
    {
        ParseQueryAdapter.QueryFactory<ParseObject> factory = new ParseQueryAdapter.QueryFactory<ParseObject>() {
            public ParseQuery create() {
                ParseQuery query = new ParseQuery("University");
                return query;
            }
        };

        adapter = new ParseQueryAdapter<ParseObject>(getActivity(), factory);
        adapter.setTextKey("name");
        uniSpinner.setAdapter(adapter);
        uniSpinner.setSelection(1);
        uniSpinner.setOnItemSelectedListener(new mySpinnerListener());
    }

    class mySpinnerListener implements Spinner.OnItemSelectedListener
    {
        @Override
        public void onItemSelected(AdapterView parent, View v, int position,long id) {

            ParseObject theSelectedObject = adapter.getItem(position);
            uniSpinnerText = theSelectedObject.get("name").toString();
        }

        @Override
        public void onNothingSelected(AdapterView parent) {
            // TODO Auto-generated method stub
            // Do nothing.
        }

    }

    @Override
    public void onClick(View v) {

        if(currentUser.getString("university").equals(uniSpinnerText))
        {
            Toast.makeText(getActivity(),"Your University is already set to that!", Toast.LENGTH_LONG).show();
        }
        else
        {
            currentUser.put("university", uniSpinnerText);
            currentUser.saveInBackground();
            Toast.makeText(getActivity(), "University changed to: " + uniSpinnerText, Toast.LENGTH_LONG).show();
        }
    }
}

menu1_student.xml：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent"
    android:orientation="vertical">

    <RelativeLayout
        android:id="@+id/selectUniFrame"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textAppearance="?android:attr/textAppearanceSmall"
            android:text="Your Selected University: "
            android:id="@+id/studentUniTextView"/>

    </RelativeLayout>

    <RelativeLayout
        android:id="@+id/changeUni"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/selectUniFrame">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textAppearance="?android:attr/textAppearanceSmall"
            android:text="Change University to"
            android:id="@+id/studentChangeUniTextView"
            android:layout_alignParentLeft="true"/>

        <Spinner
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/uniSpinner"
            android:visibility="visible"
            android:layout_below="@+id/studentChangeUniTextView"
            android:spinnerMode="dropdown"/>

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/changeUniButton"
            android:layout_toRightOf="@+id/uniSpinner"
            android:text="Change"/>

    </RelativeLayout>

</RelativeLayout>

menu1_lecture.xml：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent"
    android:orientation="vertical">

    <RelativeLayout
        android:id="@+id/selectUniFrame"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textAppearance="?android:attr/textAppearanceSmall"
            android:text="Your Selected University: "
            android:id="@+id/lectureUniTextView"/>

    </RelativeLayout>

    <RelativeLayout
        android:id="@+id/changeUni"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/selectUniFrame">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textAppearance="?android:attr/textAppearanceSmall"
            android:text="Change University to"
            android:id="@+id/lectureChangeUniTextView"
            android:layout_alignParentLeft="true"/>

        <Spinner
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/uniSpinner"
            android:visibility="visible"
            android:layout_below="@+id/lectureChangeUniTextView"
            android:spinnerMode="dropdown"/>

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/changeUniButton"
            android:layout_toRightOf="@+id/uniSpinner"
            android:text="Change"/>

    </RelativeLayout>

</RelativeLayout>

Answer 1

而不是

if(currentUser.getString("university").equals(""))

使用

if(currentUser==null || currentUser.getString("university")==null || currentUser.getString("university").equals(""))

Answer 2

您的university对象中似乎没有currentUser个键。

它可能只在某一点上填充，这就是它之前工作的原因。

如果您卸载/重新安装，或者您在某处清除了某些代码，那么它就不会填充。

要回答有关预期（未定义）行为的问题，请参阅Parse文档：

getString

public String getString（String key）

访问字符串值。

参数：key - 访问值的键。

返回：如果没有这样的键或者它不是String
，则返回null

因此，在这种情况下返回null是预期的行为。

参考：https://parse.com/docs/android/api/com/parse/ParseObject.html#getString(java.lang.String)

Android应用程序空指针无法启动活动ComponentInfo

2 个答案: