Android with Firebase : DataSnapshot.getValue() throws java.

Question

我正在从Firebase实时数据库中编写和读取类用户。这是用户类：

public class User {
public String name;
public int number;
public String title;
public String company;
public String location;
public Bitmap image;
public String name_title_company_location;
public User() {
// Default constructor required for calls to DataSnapshot.getValue(User.class)
}
public User(String name, int number, String title, String company, String location, Bitmap image) {
this.name = name;
this.number = number;
this.title = title;
this.company = company;
this.location = location;
this.image = image;
this.name_title_company_location = name + "_" + title + "_" +company + "_" + location;
}

这是我的Firebase实时数据库：

users
0
company: "Indifair"
image
location: "Bangalore"
name: "Anupam Singh"
name_title_company_location: "Anupam Singh_Engineer_Indifair_Bangalore"
number: 956156494
title: "Engineer"

这段代码抛出错误：

DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference();
EditText t1 = (EditText) findViewById(R.id.editText10);
EditText t2 = (EditText) findViewById(R.id.editText11);
EditText t3 = (EditText) findViewById(R.id.editText13);
EditText t4 = (EditText) findViewById(R.id.editText14);
String s1 = t1.getText().toString();
String s2 = t2.getText().toString();
String s3 = t3.getText().toString();
String s4 = t4.getText().toString();
mDatabase.child("users").orderByChild("name_title_company_location")
.equalTo(s1 + "_" + s2 + "_" + s3 + "_" + s4)
.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
User user  = dataSnapshot.getValue(User.class);
//ImageView im = (ImageView) findViewById(R.id.imageView);
//TextView tv1 = (TextView) findViewById(R.id.textView3);
//TextView tv2 = (TextView) findViewById(R.id.textView5);
///im.setImageBitmap(user.image);
///tv1.setText(user.name);
///tv2.setText(user.number);

}
public void onCancelled(DatabaseError databaseError) {
// Getting Post failed, log a message
//Log.w(TAG, "loadPost:onCancelled", databaseError.toException());
}
});

我收到此错误：

java.lang.IllegalArgumentException: Service not registered: com.google.android.gms.measurement.internal.zzjc@45abe13
at android.app.LoadedApk.forgetServiceDispatcher(LoadedApk.java:1105)
at android.app.ContextImpl.unbindService(ContextImpl.java:1873)
at android.content.ContextWrapper.unbindService(ContextWrapper.java:562)
at com.google.android.gms.common.stats.ConnectionTracker.unbindService(Unknown Source)
at com.google.android.gms.measurement.internal.zzik.zzah(com.google.android.gms:play-services-measurement-impl@@17.2.0:240)
at com.google.android.gms.measurement.internal.zzik.zzak(com.google.android.gms:play-services-measurement-impl@@17.2.0:257)
at com.google.android.gms.measurement.internal.zzik.zzc(com.google.android.gms:play-services-measurement-impl@@17.2.0:319)
at com.google.android.gms.measurement.internal.zzij.zza(com.google.android.gms:play-services-measurement-impl@@17.2.0:2)
at com.google.android.gms.measurement.internal.zzai.run(com.google.android.gms:play-services-measurement-impl@@17.2.0:7)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:422)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at com.google.android.gms.measurement.internal.zzfy.run(com.google.android.gms:play-services-measurement-impl@@17.2.0:20)

当我注释掉User user = dataSnapshot.getValue(User.class);错误时，错误消失了。

可能出现什么问题？

Answer 1

当您对 Firebase 数据库执行查询时，可能会有多个结果。因此，快照包含这些结果的列表。即使只有一个结果，快照也将包含一个结果的列表。

因此，您的onDataChange需要处理DataSnapshot可以包含多个用户的事实。您可以通过像这样循环遍历dataSnapshot.getChildren()来轻松执行此操作：

mDatabase.child("users").orderByChild("name_title_company_location")
.equalTo(s1 + "_" + s2 + "_" + s3 + "_" + s4)
.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot userSnapshot: dataSnapshot.getChildren) {
User user = userSnapshot.getValue(User.class);
...
}
}