NullPointerException出现在android中 [英] NullPointerException comes up in android

问题描述

您好我是Android应用程序开发的新手，我正在构建一个教育应用程序启动器，并且在一个活动上NullPointerException使应用程序在运行时停止，我不知道如何解决这个问题。



这是我的代码：

Hello I am new to android app development, and I am currently building an educational app launcher and on an activity the NullPointerException makes the app to stop while running and I don't know how to solve this.

This is my code:

package com.example.homestudent;

import com.parse.GetCallback;
import com.parse.Parse;
import com.parse.ParseObject;
import com.parse.ParseQuery;
import com.parse.ParseException;

import android.os.Bundle;
import android.os.NetworkOnMainThreadException;
import android.os.StrictMode;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.graphics.Typeface;



public class UserLogin extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.user_login);

       // Use StrictMode to counter the actions of the NetworkOnMainThread Exception
       StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
       StrictMode.setThreadPolicy(policy);

       // Connect to Parse Database
       Parse.initialize(this, "fjXPa3CFuEjoLwVsNOqWI4GqbTPEnWPgyicL75Kk", "2sbmKPxjFT9OFWHhb7qQjDIqnjTEAhVgWRS27r4u");

       // Create Segoe Ui Light Typeface
       Typeface tfSegoeUILight = Typeface.createFromAsset(getAssets(), "fonts/segoeuil.ttf");

       // Create Big Noodle Titling Typeface
       Typeface tfBigNoodleTitling = Typeface.createFromAsset(getAssets(), "fonts/big_noodle_titling.ttf");

       // Create TextView class and connect to layout
       final TextView tvSchoolName = (TextView) findViewById(R.id.tvSchoolName);
       tvSchoolName.setTypeface(tfSegoeUILight);

       // Create EditTesk class and connect to layout
       final EditText etUserName = (EditText) findViewById(R.id.etUserName);
       etUserName.setTypeface(tfSegoeUILight);

       // Create Button class and connect to layout
       Button btnSubmit = (Button) findViewById(R.id.btnSubmit1);
       btnSubmit.setTypeface(tfBigNoodleTitling);

       // Put the value of "code" from the intent into String variable
       String SchoolCode1 = getIntent().getExtras().getString("code");

       // Convert the string value of SchoolCode1 and put it into an int variable
       int SchoolCode = Integer.parseInt(SchoolCode1);

       // ParseQuery to get the School Name from the database
       ParseQuery<ParseObject> query = ParseQuery.getQuery("SchoolData");
       query.whereEqualTo("Code", SchoolCode);
       query.getFirstInBackground(new GetCallback<ParseObject>() {
           public void done(ParseObject object, ParseException e) {
               if (object == null) {
                   tvSchoolName.setText("No School");
               } 
               else {
                   String SchoolName = object.getString("SchoolName");
                   tvSchoolName.setText(String.valueOf(SchoolName));
               }
            }
        }); 
    }


    @Override
    public void onBackPressed() {
        // do nothing.
    }

logcat是

The logcat is

04-16 12:52:03.731: D/dalvikvm(20239): GC_CONCURRENT freed 378K, 7% free 6948K/7431K, paused 2ms+3ms
04-16 12:52:04.544: D/OpenGLRenderer(20239): Flushing caches (mode 0)
04-16 12:52:05.676: D/dalvikvm(20239): GC_CONCURRENT freed 384K, 7% free 7014K/7495K, paused 2ms+4ms
04-16 12:52:09.731: D/OpenGLRenderer(20239): Flushing caches (mode 1)
04-16 12:52:09.895: D/AndroidRuntime(20239): Shutting down VM
04-16 12:52:09.895: W/dalvikvm(20239): threadid=1: thread exiting with uncaught exception (group=0x40bea1f8)
04-16 12:52:09.895: E/AndroidRuntime(20239): FATAL EXCEPTION: main
04-16 12:52:09.895: E/AndroidRuntime(20239): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.homestudent/com.example.homestudent.UserLogin}: java.lang.NullPointerException
04-16 12:52:09.895: E/AndroidRuntime(20239):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at android.app.ActivityThread.access$600(ActivityThread.java:128)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at android.os.Handler.dispatchMessage(Handler.java:99)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at android.os.Looper.loop(Looper.java:137)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at android.app.ActivityThread.main(ActivityThread.java:4514)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at java.lang.reflect.Method.invokeNative(Native Method)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at java.lang.reflect.Method.invoke(Method.java:511)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at dalvik.system.NativeStart.main(Native Method)
04-16 12:52:09.895: E/AndroidRuntime(20239): Caused by: java.lang.NullPointerException
04-16 12:52:09.895: E/AndroidRuntime(20239):    at com.example.homestudent.UserLogin.onCreate(UserLogin.java:58)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at android.app.Activity.performCreate(Activity.java:4465)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1053)
04-16 12:52:09.895: E/AndroidRuntime(20239):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
04-16 12:52:09.895: E/AndroidRuntime(20239):    ... 11 more
04-16 12:54:11.387: I/Process(20239): Sending signal. PID: 20239 SIG: 9
04-16 12:54:31.098: D/libEGL(21248): loaded /vendor/lib/egl/libEGL_POWERVR_SGX540_120.so
04-16 12:54:31.106: D/libEGL(21248): loaded /vendor/lib/egl/libGLESv1_CM_POWERVR_SGX540_120.so
04-16 12:54:31.106: D/libEGL(21248): loaded /vendor/lib/egl/libGLESv2_POWERVR_SGX540_120.so
04-16 12:54:31.309: D/OpenGLRenderer(21248): Enabling debug mode 0
04-16 12:54:40.739: D/dalvikvm(21248): GC_CONCURRENT freed 285K, 6% free 6849K/7239K, paused 4ms+4ms
04-16 12:54:41.856: D/OpenGLRenderer(21248): Flushing caches (mode 0)
04-16 12:54:55.684: D/OpenGLRenderer(21248): Flushing caches (mode 0)
04-16 12:55:01.223: D/dalvikvm(21248): GC_CONCURRENT freed 364K, 7% free 6953K/7431K, paused 2ms+3ms
04-16 12:55:02.208: D/OpenGLRenderer(21248): Flushing caches (mode 0)
04-16 12:55:03.958: D/dalvikvm(21248): GC_CONCURRENT freed 380K, 7% free 7023K/7495K, paused 2ms+5ms
04-16 12:55:08.372: D/OpenGLRenderer(21248): Flushing caches (mode 1)
04-16 12:55:08.520: D/AndroidRuntime(21248): Shutting down VM
04-16 12:55:08.520: W/dalvikvm(21248): threadid=1: thread exiting with uncaught exception (group=0x40bea1f8)
04-16 12:55:08.520: E/AndroidRuntime(21248): FATAL EXCEPTION: main
04-16 12:55:08.520: E/AndroidRuntime(21248): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.homestudent/com.example.homestudent.UserLogin}: java.lang.NullPointerException
04-16 12:55:08.520: E/AndroidRuntime(21248):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at android.app.ActivityThread.access$600(ActivityThread.java:128)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at android.os.Handler.dispatchMessage(Handler.java:99)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at android.os.Looper.loop(Looper.java:137)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at android.app.ActivityThread.main(ActivityThread.java:4514)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at java.lang.reflect.Method.invokeNative(Native Method)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at java.lang.reflect.Method.invoke(Method.java:511)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at dalvik.system.NativeStart.main(Native Method)
04-16 12:55:08.520: E/AndroidRuntime(21248): Caused by: java.lang.NullPointerException
04-16 12:55:08.520: E/AndroidRuntime(21248):    at com.example.homestudent.UserLogin.onCreate(UserLogin.java:58)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at android.app.Activity.performCreate(Activity.java:4465)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1053)
04-16 12:55:08.520: E/AndroidRuntime(21248):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
04-16 12:55:08.520: E/AndroidRuntime(21248):    ... 11 more

推荐答案

600（ActivityThread.java： 128 ）
04 - 16 12 ： 52 ：< span class =code-digit> 09 。 895 ：E / AndroidRuntime（ 20239 ）：atr oid.app.ActivityThread

600(ActivityThread.java:128) 04-16 12:52:09.895: E/AndroidRuntime(20239): at android.app.ActivityThread

H.handleMessage（ActivityThread.java： 1161 ）
04 - 16 12 ： 52 ： 09 。 895 ：E / AndroidRuntime（ 20239 ）：在android.os.Handler.dispatchMessage（Handler.java： 99 ）
04 - 16 12 ： 52 ： 09 。 895 ：E / AndroidRuntime（ 20239 ）：在android.os.Looper.loop（Looper.java： 137 ）
04 - 16 12 ： 52 ： 09 。 895 ：E / AndroidRuntime（ 20239 ）：在android .app.ActivityThread.main（ActivityThread.java： 4514 ）
04 - 16 12 ： 52 ： 09 。 895 ：E / AndroidRuntime（ 20239 ）：at java。 lang.reflect.Method.invokeNative（Native Method）
04 - 16 12 ： 52 ： 09 。 895 ：E / AndroidRuntime（ 20239 ）：at java.lang.reflect.Method.invoke（Method.java： 511 ）
04 - 16 12 ： 52 ： 09 。 895 ：E / AndroidRuntime（ 20239 ）：at com.android.internal.os.ZygoteInit

H.handleMessage(ActivityThread.java:1161) 04-16 12:52:09.895: E/AndroidRuntime(20239): at android.os.Handler.dispatchMessage(Handler.java:99) 04-16 12:52:09.895: E/AndroidRuntime(20239): at android.os.Looper.loop(Looper.java:137) 04-16 12:52:09.895: E/AndroidRuntime(20239): at android.app.ActivityThread.main(ActivityThread.java:4514) 04-16 12:52:09.895: E/AndroidRuntime(20239): at java.lang.reflect.Method.invokeNative(Native Method) 04-16 12:52:09.895: E/AndroidRuntime(20239): at java.lang.reflect.Method.invoke(Method.java:511) 04-16 12:52:09.895: E/AndroidRuntime(20239): at com.android.internal.os.ZygoteInit

MethodAndArgsCaller .run（ZygoteInit.java： 790 ）
04 - 16 12 ： 52 ： 09 。 895 ：E / AndroidRuntime（ 20239 ）：at com.android.internal。 os.ZygoteInit.main（ZygoteInit.java： 557 ）
04 - 16 12 ： 52 ： 09 。 895 ：E / AndroidRuntime（ 20239 ）：at dalvik.system .Native Start.main（本机方法）
04 - 16 12 ： 52 ： 09 。 895: E/AndroidRuntime(20239): Caused by: java.lang.NullPointerException
04 -16 12:52:09.895: E/AndroidRuntime(20239): at com.example.homestudent.UserLogin.onCreate(UserLogin.java:58)
04-16 12:52:09.895: E/AndroidRuntime(20239 ): at andr oid.app.Activity.performCreate(Activity.java:4465)
04-16 12:52:09.895: E/AndroidRuntime(20239): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1053)
04-16 12:52:09.895: E/AndroidRuntime(20239): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
04-16 12:52:09.895: E/AndroidRuntime(20239): ... 11 more
04-16 12:54:11.387: I/Process(20239): Sending signal. PID: 20239 SIG: 9
04-16 12:54:31.098: D/libEGL(21248): loaded /vendor/lib/egl/libEGL_POWERVR_SGX540_120.so
04-16 12:54:31.106: D/libEGL(21248): loaded /vendor/lib/egl/libGLESv1_CM_POWERVR_SGX540_120.so
04-16 12:54:31.106: D/libEGL(21248): loaded /ve ndor/lib/egl/libGLESv2_POWERVR_SGX540_120.so
04-16 12:54:31.309: D/OpenGLRenderer(21248): Enabling debug mode 0
04-16 12:54:40.739: D/dalvikvm(21248): GC_CONCURRENT freed 285K, 6% free 6849K/7239K, paused 4ms+4ms
04-16 12:54:41.856: D/OpenGLRenderer(21248): Flushing caches (mode < span class=\"code-digit\">0)
04-16 12:54:55.684: D/OpenGLRenderer(21248): Flushing caches (mode 0)
04-16 12:55:01.223: D/dalvikvm(21248): GC_CONCURRENT freed 364K, 7% free 6953K/7431K, paused 2ms+3ms
04-16 12:55:02.208: D/OpenGLRenderer(21248): Flushing caches (mode 0)
04-16 12:55:03.958: D/dalvikvm(21248): GC_CONCURRENT freed 380K, 7% free 7023K/7495K, paused 2ms+5ms
04-16 12:55:08.372: D/OpenGLRenderer(21248): Flushing caches (mode 1)
04-16 12:55:08.520: D/AndroidRuntime(21248): Shutting down VM
04-16 12:55:08.520: W/dalvikvm(21248): threadid=1: thread exiting with uncaught exception (group=0x40bea1f8)
04-16 12:55:08.520: E/AndroidRuntime(21248): FATAL EXCEPTION: main
04-16 12:55:08.520: E/AndroidRuntime(21248): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.homestudent/com.example.homestudent .UserLogin}: java.lang.NullPointerException
04-16 12:55:08.520: E/AndroidRuntime(21248): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970)
04-16 12:55:08.520: E/AndroidRuntime(21248): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
04-16 12:55:08.520: E/AndroidRuntime(21248): at android.app.ActivityThread.access

MethodAndArgsCaller.run(ZygoteInit.java:790) 04-16 12:52:09.895: E/AndroidRuntime(20239): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557) 04-16 12:52:09.895: E/AndroidRuntime(20239): at dalvik.system.NativeStart.main(Native Method) 04-16 12:52:09.895: E/AndroidRuntime(20239): Caused by: java.lang.NullPointerException 04-16 12:52:09.895: E/AndroidRuntime(20239): at com.example.homestudent.UserLogin.onCreate(UserLogin.java:58) 04-16 12:52:09.895: E/AndroidRuntime(20239): at android.app.Activity.performCreate(Activity.java:4465) 04-16 12:52:09.895: E/AndroidRuntime(20239): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1053) 04-16 12:52:09.895: E/AndroidRuntime(20239): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934) 04-16 12:52:09.895: E/AndroidRuntime(20239): ... 11 more 04-16 12:54:11.387: I/Process(20239): Sending signal. PID: 20239 SIG: 9 04-16 12:54:31.098: D/libEGL(21248): loaded /vendor/lib/egl/libEGL_POWERVR_SGX540_120.so 04-16 12:54:31.106: D/libEGL(21248): loaded /vendor/lib/egl/libGLESv1_CM_POWERVR_SGX540_120.so 04-16 12:54:31.106: D/libEGL(21248): loaded /vendor/lib/egl/libGLESv2_POWERVR_SGX540_120.so 04-16 12:54:31.309: D/OpenGLRenderer(21248): Enabling debug mode 0 04-16 12:54:40.739: D/dalvikvm(21248): GC_CONCURRENT freed 285K, 6% free 6849K/7239K, paused 4ms+4ms 04-16 12:54:41.856: D/OpenGLRenderer(21248): Flushing caches (mode 0) 04-16 12:54:55.684: D/OpenGLRenderer(21248): Flushing caches (mode 0) 04-16 12:55:01.223: D/dalvikvm(21248): GC_CONCURRENT freed 364K, 7% free 6953K/7431K, paused 2ms+3ms 04-16 12:55:02.208: D/OpenGLRenderer(21248): Flushing caches (mode 0) 04-16 12:55:03.958: D/dalvikvm(21248): GC_CONCURRENT freed 380K, 7% free 7023K/7495K, paused 2ms+5ms 04-16 12:55:08.372: D/OpenGLRenderer(21248): Flushing caches (mode 1) 04-16 12:55:08.520: D/AndroidRuntime(21248): Shutting down VM 04-16 12:55:08.520: W/dalvikvm(21248): threadid=1: thread exiting with uncaught exception (group=0x40bea1f8) 04-16 12:55:08.520: E/AndroidRuntime(21248): FATAL EXCEPTION: main 04-16 12:55:08.520: E/AndroidRuntime(21248): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.homestudent/com.example.homestudent.UserLogin}: java.lang.NullPointerException 04-16 12:55:08.520: E/AndroidRuntime(21248): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970) 04-16 12:55:08.520: E/AndroidRuntime(21248): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995) 04-16 12:55:08.520: E/AndroidRuntime(21248): at android.app.ActivityThread.access

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