Question

我有一个传感器，它捕获数据并每隔几秒钟发布到Firebase。因此，我制作了一个android客户端来显示数据。但是，我尝试了几次，但是代码始终返回'java.lang.NullPointerException'。希望有丰富编码经验的人可以看到发生了什么，谢谢。

Android代码：

public class MainActivity extends AppCompatActivity {
    private TextView temperature;
    private TextView humidity ;
    private Button updatebutton;
    DatabaseReference myRef;
    String tempData;
    String humidData ;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
     temperature = (TextView)findViewById(R.id.tempdata);
     humidity = (TextView)findViewById(R.id.humiddata);
     updatebutton=(Button)findViewById(R.id.update_btn);




    updatebutton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            myRef= FirebaseDatabase.getInstance().getReference().child("sensor_1").child("dht");
            myRef.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                   String tempdata= Objects.requireNonNull(dataSnapshot.child("temp").getValue()).toString();
                   String humidData= Objects.requireNonNull(dataSnapshot.child("humidity").getValue()).toString();
                   temperature.setText(tempdata);
                   humidity.setText(humidData);


                    }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
                });


        }
    });

}
}

Firebase

错误

Process: com.example.rpi_weatherapp, PID: 11254
    java.lang.NullPointerException
        at java.util.Objects.requireNonNull(Objects.java:98)
        at com.example.rpi_weatherapp.MainActivity$1$1.onDataChange(MainActivity.java:52)
        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@16.0.4:75)
        at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@16.0.4:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@16.0.4:55)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5399)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:927)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:722)

XML代码

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#B70199EB"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/humiddata"
        android:layout_width="131dp"
        android:layout_height="97dp"
        android:layout_marginStart="24dp"
        android:layout_marginTop="328dp"
        android:layout_marginEnd="24dp"
        android:text="humid_data"
        android:textSize="15sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/temp_textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="52dp"
        android:layout_marginEnd="8dp"
        android:text="Temperature"
        android:textColor="#FFFFFF"
        android:textSize="15sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/tempdata"
        android:layout_width="131dp"
        android:layout_height="97dp"
        android:layout_marginStart="24dp"
        android:layout_marginTop="108dp"
        android:layout_marginEnd="24dp"
        android:text="temp_data"
        android:textSize="24sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/degreecelcius"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="24dp"
        android:layout_marginTop="108dp"
        android:layout_marginEnd="24dp"
        android:text="℃"
        android:textSize="15sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.722"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/humidity_textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="24dp"
        android:layout_marginTop="284dp"
        android:layout_marginEnd="24dp"
        android:text="Humidity"
        android:textColor="#FFFFFF"
        android:textSize="15sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/percentage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="24dp"
        android:layout_marginTop="328dp"
        android:layout_marginEnd="24dp"
        android:text="%"
        android:textSize="15sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.724"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/update_btn"
        style="@style/Widget.AppCompat.Button.Colored"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="24dp"
        android:layout_marginTop="500dp"
        android:layout_marginEnd="24dp"
        android:layout_marginBottom="24dp"
        android:text="Update "
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.201" />
</android.support.constraint.ConstraintLayout>

完整Logcat

05-17 01:40:44.118 20828-20828/? I/PMFunc: prepare 0 com.example.rpi_weatherapp
05-17 01:40:44.118 20828-20828/? I/art: Late-enabling -Xcheck:jni
05-17 01:40:44.148 20828-20828/? D/Environment: 111 rawUserId = 0
05-17 01:40:44.148 20828-20828/? D/AndroidKeyStoreProvider: overseas product
05-17 01:40:44.148 20828-20842/? I/art: Debugger is no longer active
05-17 01:40:44.208 20828-20828/? W/ComponentDiscovery: Application info not found.
05-17 01:40:44.208 20828-20828/? W/ComponentDiscovery: Could not retrieve metadata, returning empty list of registrars.
05-17 01:40:44.218 20828-20828/? D/FirebaseApp: com.google.firebase.auth.FirebaseAuth is not linked. Skipping initialization.
05-17 01:40:44.218 20828-20828/? D/FirebaseApp: com.google.firebase.iid.FirebaseInstanceId is not linked. Skipping initialization.
05-17 01:40:44.218 20828-20828/? D/FirebaseApp: com.google.firebase.crash.FirebaseCrash is not linked. Skipping initialization.
05-17 01:40:44.218 20828-20828/? D/FirebaseApp: com.google.android.gms.measurement.AppMeasurement is not linked. Skipping initialization.
05-17 01:40:44.218 20828-20828/? I/FirebaseInitProvider: FirebaseApp initialization successful
05-17 01:40:44.298 20828-20828/? W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
05-17 01:40:44.308 20828-20828/? D/PhoneWindow: DEBUG_SYSTEMUI:origin statusbar style 
05-17 01:40:44.308 20828-20828/? D/PhoneWindow: DEBUG_SYSTEMUI:windowDrawsFlag set
05-17 01:40:44.308 20828-20828/? D/PhoneWindow: DEBUG_SYSTEMUI:IconColor=1
05-17 01:40:44.308 20828-20828/? D/PhoneWindow: DEBUG_SYSTEMUI:StatusBarColor final set ff00574b
05-17 01:40:44.328 20828-20828/? I/art: Rejecting re-init on previously-failed class java.lang.Class<android.support.v4.view.ViewCompat$OnUnhandledKeyEventListenerWrapper>
05-17 01:40:44.328 20828-20828/? I/art: Rejecting re-init on previously-failed class java.lang.Class<android.support.v4.view.ViewCompat$OnUnhandledKeyEventListenerWrapper>
05-17 01:40:44.458 20828-20828/? I/ViewRootImpl: CPU Rendering VSync enable = true
05-17 01:40:44.458 20828-20855/? D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true
05-17 01:40:44.468 20828-20828/? D/Atlas: Validating map...
05-17 01:40:44.508 20828-20855/? I/Adreno: QUALCOMM build                   : 814500f, If3abccc389
    Build Date                       : 03/15/17
    OpenGL ES Shader Compiler Version: XE031.06.00.03
    Local Branch                     : 
    Remote Branch                    : refs/tags/AU_LINUX_ANDROID_LA.BR.1.3.2.C2.05.01.01.199.103
    Remote Branch                    : NONE
    Reconstruct Branch               : NOTHING
05-17 01:40:44.518 20828-20855/? I/OpenGLRenderer: Initialized EGL, version 1.4
05-17 01:40:44.528 20828-20855/? D/OpenGLRenderer: Enabling debug mode 0
05-17 01:40:44.588 20828-20828/? I/Timeline: Timeline: Activity_idle id: android.os.BinderProxy@2ab3aeb3 time:26150979
05-17 01:40:45.898 20828-20828/com.example.rpi_weatherapp D/AndroidRuntime: Shutting down VM
05-17 01:40:45.898 20828-20828/com.example.rpi_weatherapp E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.rpi_weatherapp, PID: 20828
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
        at com.example.rpi_weatherapp.MainActivity$1$1.onDataChange(MainActivity.java:53)
        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@16.0.4:75)
        at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@16.0.4:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@16.0.4:55)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5399)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:927)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:722)
05-17 01:40:45.918 20828-20828/com.example.rpi_weatherapp I/Process: Sending signal. PID: 20828 SIG: 9

传感器代码（Python）

import RPi.GPIO as GPIO
from time import sleep
import datetime
from firebase import firebase
import Adafruit_DHT

import urllib2, urllib, httplib
import json
import os 
from functools import partial

GPIO.setmode(GPIO.BCM)
GPIO.cleanup()
GPIO.setwarnings(False)

# Sensor should be set to Adafruit_DHT.DHT11,
# Adafruit_DHT.DHT22, or Adafruit_DHT.AM2302.
sensor = Adafruit_DHT.DHT11

# Example using a Beaglebone Black with DHT sensor
# connected to pin P8_11.
pin = 17

# Try to grab a sensor reading.  Use the read_retry method which will retry up
# to 15 times to get a sensor reading (waiting 2 seconds between each retry).
humidity, temperature = Adafruit_DHT.read_retry(sensor, pin)


firebase = firebase.FirebaseApplication('https://project.firebaseio.com/', None)
#firebase.put("/dht", "/temp", "0.00")
#firebase.put("/dht", "/humidity", "0.00")

def update_firebase():

    humidity, temperature = Adafruit_DHT.read_retry(sensor, pin)
    if humidity is not None and temperature is not None:
        sleep(5)
        str_temp = ' {0:0.2f} *C '.format(temperature)  
        str_hum  = ' {0:0.2f} %'.format(humidity)
        print('Temp={0:0.1f}*C  Humidity={1:0.1f}%'.format(temperature, humidity))  

    else:
        print('Failed to get reading. Try again!')  
        sleep(10)

    data = {"temp": temperature, "humidity": humidity}
    firebase.post('/sensor_1/dht', data)


while True:
        update_firebase()

        #sleepTime = int(sleepTime)
        sleep(5)

如何解决“ java.lang.NullPointerException”的问题？

0 个答案: