问题
I am currently experimenting with Firebase by creating a kind of small chat app. I am able to send data to the database reference, however I would expect it to be displayed thanks to the following code. However that is not the case, I was wondering if there was something wrong with the way I am using the adapter for my list.
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if(FirebaseAuth.getInstance().getCurrentUser() == null) {
// Start sign in/sign up activity
startActivityForResult(
AuthUI.getInstance().createSignInIntentBuilder().build(),
SIGN_IN_REQUEST_CODE
);
} else {
// User is already signed in. Therefore, display
// a welcome Toast
Toast.makeText(this,
"Welcome " + FirebaseAuth.getInstance()
.getCurrentUser()
.getDisplayName(),
Toast.LENGTH_LONG)
.show();
displayChatMessages();
}
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);
// Read the input field and push a new instance
// of ChatMessage to the Firebase database
FirebaseDatabase.getInstance()
.getReference()
.push()
.setValue(new ChatMessage(input.getText().toString(),
FirebaseAuth.getInstance()
.getCurrentUser()
.getDisplayName())
);
// Clear the input
input.setText("");
}
});
}
private void displayChatMessages() {
ListView listOfMessages = (ListView)findViewById(R.id.list_of_messages);
Query query = FirebaseDatabase.getInstance().getReference();
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) {
// Get references to the views of message.xml
TextView messageText = (TextView)v.findViewById(R.id.message_text);
TextView messageUser = (TextView)v.findViewById(R.id.message_user);
TextView messageTime = (TextView)v.findViewById(R.id.message_time);
// Set their text
messageText.setText(model.getMessageText());
messageUser.setText(model.getMessageUser());
messageTime.setText(DateFormat.format("dd-MM-yyyy (HH:mm:ss)",
model.getMessageTime()));
}
};
listOfMessages.setAdapter(adapter);
}
@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,
"Successfully signed in. Welcome!",
Toast.LENGTH_LONG)
.show();
displayChatMessages();
} else {
Toast.makeText(this,
"We couldn't sign you in. Please try again later.",
Toast.LENGTH_LONG)
.show();
// Close the app
finish();
}
}
}
}
Here is the UI of the main activity
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="citroentrex.citron.MainActivity">
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:clickable="true"
android:tint="@android:color/white"
app:fabSize="mini"
/>
<android.support.design.widget.TextInputLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_toLeftOf="@id/fab"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true">
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="Input"
android:id="@+id/input"
/>
</android.support.design.widget.TextInputLayout>
<ListView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:dividerHeight="16dp"
android:divider="@android:color/transparent"
android:layout_above="@id/fab"
android:id="@+id/list_of_messages"
android:layout_marginBottom="16dp"
/>
</RelativeLayout>
and of the message
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent" android:layout_height="match_parent">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:id="@+id/message_user"
android:textStyle="normal|bold" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="@+id/message_user"
android:layout_alignParentRight="true"
android:id="@+id/message_time" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/message_user"
android:layout_alignParentLeft="true"
android:layout_marginTop="5dp"
android:id="@+id/message_text"
android:textAppearance="@style/TextAppearance.AppCompat.Body1"
android:textSize="18sp" />
</RelativeLayout>
displayChatMessages is the bit wher I would expect the adapter to display the data content in my list. (Pushing data to the database works for sure) This is the model of my database. (there are no child)
回答1:
The adapter had to be initialised as follow:
@Override
protected void onStart() {
super.onStart();
adapter.startListening();
}
@Override
protected void onStop() {
super.onStop();
adapter.stopListening();
}
来源：https://stackoverflow.com/questions/48271185/display-firebase-database-content-in-a-firebaselistadapter