当应用程序打开时，Firebase 在 addListenerForSingleValueEvent 上崩溃 [重复]

Question

我试图从我的 firebase 读取一次数据，但我的应用程序不断崩溃，下面是我的数据库的样子 enter image description here

下面是我的代码

public void checkUserStatus(){

        final String ID = firebaseAuth.getCurrentUser().getUid();
        FirebaseDatabase database = FirebaseDatabase.getInstance();
        DatabaseReference myRef = database.getReference();
        myRef.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                User user = dataSnapshot.child("UserDetails").child(ID).child("Type").getValue(User.class);
                textView.setText(user.getTrueFalse());
            }

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

            }
        });
    }

错误

2019-12-06 20:31:32.595 13211-13211/com.example.smartdoor E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.smartdoor, PID: 13211
    com.google.firebase.database.DatabaseException: Class com.example.smartdoor.User does not define a no-argument constructor. If you are using ProGuard, make sure these constructors are not stripped.
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(com.google.firebase:firebase-database@@19.2.0:569)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(com.google.firebase:firebase-database@@19.2.0:562)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(com.google.firebase:firebase-database@@19.2.0:432)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(com.google.firebase:firebase-database@@19.2.0:231)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(com.google.firebase:firebase-database@@19.2.0:79)
        at com.google.firebase.database.DataSnapshot.getValue(com.google.firebase:firebase-database@@19.2.0:203)
        at com.example.smartdoor.SignOutFragment$2.onDataChange(SignOutFragment.java:79)
        at com.google.firebase.database.Query$1.onDataChange(com.google.firebase:firebase-database@@19.2.0:179)
        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@19.2.0:75)
        at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@19.2.0:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@19.2.0:55)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

Answer 1

为类User添加一个无参数构造函数：

public User() {
}