这是我在firebase中的第一个项目。我试图从firebase中删除值,但是当我试图从firebase中删除值时,我的应用程序崩溃了。我没有得到如何解决这个错误
Service.class
public class NotiListener extends Service {
@Override
public IBinder onBind(Intent intent) {
return null;
}
//When the service is started
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
//Opening sharedpreferences
SharedPreferences sharedPreferences = getSharedPreferences(Constant.SHARED_PREF, MODE_PRIVATE);
//Getting the firebase id from sharedpreferences
String id = sharedPreferences.getString(Constant.UNIQUE_ID, null);
//Creating a firebase object
Firebase firebase = new Firebase(Constant.FIREBASE_APP + id);
//Adding a valueevent listener to firebase
//this will help us to track the value changes on firebase
firebase.addValueEventListener(new ValueEventListener() {
//This method is called whenever we change the value in firebase
@Override
public void onDataChange(DataSnapshot snapshot) {
if(snapshot.child("msg") != null){
String msg = snapshot.child("msg").getValue().toString();
if (msg.equals("none"))
return;
showNotification(msg);
} else{
Log.e("Value-->","Null");
}
}
@Override
public void onCancelled(FirebaseError firebaseError) {
Log.e("The read failed: ", firebaseError.getMessage());
}
});
return START_STICKY;
}
@Override
public void onDestroy() {
Toast.makeText(this, "MyService Stopped", Toast.LENGTH_LONG).show();
}
private void showNotification(String msg){
//Creating a notification
NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
builder.setSmallIcon(R.mipmap.ic_launcher);
Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("https://www.facebook.com"));
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, 0);
builder.setContentIntent(pendingIntent);
builder.setLargeIcon(BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher));
builder.setContentTitle("Firebase Push Notification");
builder.setContentText(msg);
NotificationManager notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
notificationManager.notify(1, builder.build());
}
}
删除值的代码是:
Firebase firebase=new Firebase(Constant.FIREBASE_APP+id);
firebase.orderByChild(id).equalTo(id).addListenerForSingleValueEvent(
new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
dataSnapshot.getRef().removeValue();
}
@Override
public void onCancelled(FirebaseError firebaseError) {
}
});
日志:
10-21 17:46:17.384 30986-30986/com.example.pitech09.bizfriend E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.pitech09.bizfriend, PID: 30986
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
at com.example.pitech09.bizfriend.NotiListener$1.onDataChange(NotiListener.java:52)
at com.firebase.client.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:56)
at com.firebase.client.core.view.DataEvent.fire(DataEvent.java:45)
at com.firebase.client.core.view.EventRaiser$1.run(EventRaiser.java:38)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5343)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:905)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700)
答案 0 :(得分:6)
dataSnapshot.getRef().setValue(null);
不是删除Firebase对象的正确方法。您不能将空值保存到数据库中。要删除它,请使用:
dataSnapshot.getRef().removeValue();
您还应检查该值是否为空,因为您将删除该对象。
if(snapshot.child("msg").getValue() != null){
String msg = snapshot.child("msg").getValue().toString();
return;
}
答案 1 :(得分:0)
当您删除值时,当您尝试在NullPointerException
中再次获取值时,会出现ValueEventListener
。
这一行:
String msg = snapshot.child("msg").getValue().toString();
你应该检查(snapshot != null && snapshot.child("msg").getValue() != null
是否可以获得价值。
答案 2 :(得分:0)
你好@Satish Lodhi你只需要传递你从firebase中删除的项目并放上这一行。
rootRef.child(clickedKey).removeValue();
答案 3 :(得分:0)
实际上如果看到firebase的removeValue()的实现,它就像将值设置为null一样。
public Task<Void> removeValue() {
return this.setValue((Object)null);
}
因此将值设置为null或使用removeValue()函数是相同的。