Question

我正在创建一个应用程序，它将许多用户及其客户端保存在firebase数据库中。我有相关客户端的用户，我想显示当前用户的客户端列表，但是当我提示显示客户端时，应用程序崩溃。我不知道这是由于错误的代码还是客户端的布局。

这一点

 userClients.addListenerForSingleValueEvent(new ValueEventListener() {

程序不喜欢ValueEventListener。

任何帮助都将不胜感激。

public class ClientList extends AppCompatActivity {

String userId;

FirebaseAuth mAuth;
FirebaseUser firebaseUser;
DatabaseReference databaseRef;
String clientAddress;
String clientPhone;
ListView myClientList;
List<String> clientArrayList;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_client_list);

    mAuth = FirebaseAuth.getInstance();

    myClientList = (ListView) findViewById(R.id.clientList);
    clientArrayList = new ArrayList<>();

    getClientList();

}

public void getClientList(){

    databaseRef = FirebaseDatabase.getInstance().getReference();
    firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
    if (firebaseUser!=null){
        userId = firebaseUser.getUid();
    }

    Query userClients = databaseRef.child("users").child(userId);


    userClients.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            // Iterate through the friends JSON tree (for current user)
            for (DataSnapshot myDatabase : dataSnapshot.getChildren()) {
                clientAddress = myDatabase.child("Address").getValue(String.class);
                clientPhone = myDatabase.child("phone").getValue(String.class);

                clientArrayList.add( clientAddress + ", " + clientPhone );
            }
            createListView();

            if (clientArrayList.isEmpty()) {
                Toast.makeText(ClientList.this, "No Clients", Toast.LENGTH_LONG).show();
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }

    });

}



public void createListView() {

    ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, getResources().getStringArray(Integer.parseInt(userId)));
    myClientList.setAdapter(adapter);

}




ClientList}: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()
                                                                                   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
                                                                                   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
                                                                                   at android.app.ActivityThread.access$800(ActivityThread.java:151)
                                                                                   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
                                                                                   at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                   at android.os.Looper.loop(Looper.java:135)
                                                                                   at android.app.ActivityThread.main(ActivityThread.java:5254)
                                                                                   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:903)
                                                                                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
                                                                                Caused by: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()

Answer 1

如果没有登录用户，firebaseUser将为空，并且不会设置userId，使其保留为空的默认值。这将导致使用null参数调用child()，这是异常的原因：

public void getClientList(){

    databaseRef = FirebaseDatabase.getInstance().getReference();
    firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
    if (firebaseUser!=null){
        userId = firebaseUser.getUid();
    }

    Query userClients = databaseRef.child("users").child(userId); // userId == null here
    ...
}

Answer 2

试试这个：

    FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
    FirebaseDatabase database = FirebaseDatabase.getInstance();

    DatabaseReference userRef = database.getReference("users").child(user.getUid());//DatabaseReference, no Query

告诉它是否有效

Answer 3

This is because user might not have signed in and hence 0x42 is null. You can do the following to resolve the same.

0x41

显示firebase数据库条目时Android应用程序崩溃

3 个答案: