Question

我阅读了有关NPE和Firebase的所有帖子，但没有任何帮助。当我启动我的应用程序时，我总是得到NPE。我还阅读了“什么是NPE以及如何解决它”，但没有任何帮助。针对“ startListening”发生错误。我知道，启动该应用程序时没有什么要阅读的，因为聊天列表为空。但是我该如何解决呢？我已经将适配器声明为全局变量。

这是我的代码：

public class ChatLayout extends AppCompatActivity {


private static final int SIGN_IN_REQUEST_CODE = 1;
public FirebaseListAdapter<ChatMessage> adapter;

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

    if (FirebaseAuth.getInstance().getCurrentUser() == null) {
        startActivityForResult(
                AuthUI.getInstance().createSignInIntentBuilder()
                        .setTheme(R.style.AppTheme)
                        .build(),
                SIGN_IN_REQUEST_CODE
        );
    } else {
        Toast.makeText(this,
                "Willkommen " + FirebaseAuth.getInstance()
                        .getCurrentUser()
                        .getDisplayName(),
                Toast.LENGTH_LONG)
                .show();

    }


    FloatingActionButton fab = (FloatingActionButton) 
    findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            EditText input = (EditText) findViewById(R.id.input);

            FirebaseDatabase.getInstance()
                    .getReference()
                    .child("Messagess")
                    .push()
                    .setValue(new ChatMessage(input.getText().toString(),
                            FirebaseAuth.getInstance()
                                    .getCurrentUser()
                                    .getDisplayName())
                    );
            ListView listOfMessages = (ListView) findViewById(R.id.list_of_messages);

            Query query = FirebaseDatabase.getInstance().getReference().child("Messagess");
            FirebaseListOptions<ChatMessage> options = new FirebaseListOptions.Builder<ChatMessage>()
                    .setQuery(query, ChatMessage.class)
                    .setLayout(R.layout.message)

                    .build();
            adapter = new FirebaseListAdapter<ChatMessage>(options) {
                @Override
                protected void populateView(View v, ChatMessage model, int position) {
                    TextView messageText = (TextView) v.findViewById(R.id.message_text);
                    TextView messageTime = (TextView) v.findViewById(R.id.message_time);
                    TextView messageUser = v.findViewById(R.id.message_user);

                    messageText.setText(model.getMessageText());
                    messageUser.setText(model.getMessageUser());

                    messageTime.setText(DateFormat.format("dd-MM-yyyy (HH:mm:ss)", model.getMessageTime()));
                }
            };
            listOfMessages.setAdapter(adapter);
            adapter.startListening();

            input.setText("");
        }
    });

}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == SIGN_IN_REQUEST_CODE) {
        if (resultCode == RESULT_OK) {
            Toast.makeText(this,
                    "Login erfolgreich",
                    Toast.LENGTH_LONG)
                    .show();


        } else {
            Toast.makeText(this,
                    "Login fehlgeschlagen. Bitte versuchen Sie es erneut.",
                    Toast.LENGTH_LONG)
                    .show();
            finish();
        }
    }
}



@Override
protected void onStart() {
    super.onStart();
    adapter.startListening();

}


@Override
protected void onStop() {
    super.onStop();
    adapter.stopListening();
}

}

Answer 1

我通过更改

解决了

 listOfMessages.setAdapter(adapter);
        adapter.startListening();

到

        adapter.startListening();
 listOfMessages.setAdapter(adapter);

现在可以了。

Firebase聊天应用程序返回NPE

1 个答案: