android - Android 上的 ListView 中未显示 Firebase 数据

Question

Data Structure Link

Part of user1

我正在尝试在 android 上构建我的 firebase 项目，我必须在其中查看通知列表，但我无法在 ListView 中查看它。如果我创建一个本地数组对象，它会出现在列表中。我通过调试选项检查了它，我可以看到数据进入数组。

主要内容:

public class Notification extends AppCompatActivity {

private static final String TAG = "Notifications";

private FirebaseDatabase mFirebaseDatabase;
private DatabaseReference mNotificationDatabaseReference;
private ChildEventListener mChildEventListener;
private FirebaseAuth mAuth;
private String userUid;

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

    mAuth = FirebaseAuth.getInstance();
    userUid = mAuth.getCurrentUser().getUid();

    mFirebaseDatabase = FirebaseDatabase.getInstance();
    mNotificationDatabaseReference = mFirebaseDatabase.getReference().child("USER").child("User1").child("notifications");

    final ArrayList<Word> words = new ArrayList<Word>();

    // Read from the database
    mNotificationDatabaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            for (DataSnapshot postSnapshot: dataSnapshot.getChildren()) {
                Word value = postSnapshot.getValue(Word.class);
                words.add(value);
                // TODO: handle the post
            }// This method is called once with the initial value and again
            // whenever data at this location is updated.

            Log.d(TAG, "Value is: " + words);
        }

        @Override
        public void onCancelled(DatabaseError error) {
            // Failed to read value
            Log.w(TAG, "Failed to read value.", error.toException());
        }
    });


    WordAdapter adapter = new WordAdapter(this, words);
    ListView listView = findViewById(R.id.notification);
    listView.setAdapter(adapter);
}
}

适配器:

public class WordAdapter extends ArrayAdapter<Word>{

private static final String LOG_TAG = WordAdapter.class.getSimpleName();

/**
 * This is our own custom constructor (it doesn't mirror a superclass constructor).
 * The context is used to inflate the layout file, and the list is the data we want
 * to populate into the lists.
 *
 * @param context        The current context. Used to inflate the layout file.
 * @param words A List of words objects to display in a list
 */
public WordAdapter(Activity context, ArrayList<Word> words) {
    // Here, we initialize the ArrayAdapter's internal storage for the context and the list.
    // the second argument is used when the ArrayAdapter is populating a single TextView.
    // Because this is a custom adapter for two TextViews and an ImageView, the adapter is not
    // going to use this second argument, so it can be any value. Here, we used 0.
    super(context, 0, words);
}

/**
 * Provides a view for an AdapterView (ListView, GridView, etc.)
 *
 * @param position The position in the list of data that should be displayed in the
 *                 list item view.
 * @param convertView The recycled view to populate.
 * @param parent The parent ViewGroup that is used for inflation.
 * @return The View for the position in the AdapterView.
 */
@Override
public View getView(int position, View convertView, ViewGroup parent) {
    // Check if the existing view is being reused, otherwise inflate the view
    View listItemView = convertView;
    if(listItemView == null) {
        listItemView = LayoutInflater.from(getContext()).inflate(
                R.layout.list_item, parent, false);
    }

    // Get the {@link AndroidFlavor} object located at this position in the list
    Word currentWord = getItem(position);

    // Find the TextView in the list_item.xml layout with the ID version_name
    TextView notificationHeadView = (TextView) listItemView.findViewById(R.id.notification_head);
    // Get the version name from the current AndroidFlavor object and
    // set this text on the name TextView
    notificationHeadView.setText(currentWord.getNotificationHead());

    // Find the TextView in the list_item.xml layout with the ID version_number
    TextView notificationDateView = (TextView) listItemView.findViewById(R.id.notification_date);
    // Get the version number from the current AndroidFlavor object and
    // set this text on the number TextView
    notificationDateView.setText(currentWord.getNotificationDate());

    // Find the TextView in the list_item.xml layout with the ID version_number
    TextView notificationBodyView = (TextView) listItemView.findViewById(R.id.notification_body);
    // Get the version number from the current AndroidFlavor object and
    // set this text on the number TextView
    notificationBodyView.setText(currentWord.getNotificationBody());

    // Return the whole list item layout (containing 2 TextViews and an ImageView)
    // so that it can be shown in the ListView
    return listItemView;
}

}

单词:

public class Word {

private String notificationHead;
private String notificationDate;
private String notificationBody;

public Word(){

}
public Word(String notificationHead, String notificationDate, String notificationBody){
    this.notificationHead = notificationHead;
    this.notificationDate = notificationDate;
    this.notificationBody = notificationBody;
}

public String getNotificationHead(){
    return notificationHead;
}
public void setNotificationHead(String notificationHead) {
    this.notificationHead = notificationHead;
}

public String getNotificationDate(){
    return notificationDate;
}
public void setNotificationDate(String notificationDate) {
    this.notificationDate = notificationDate;
}

public String getNotificationBody() {
    return notificationBody;
}
public void setNotificationBody(String notificationBody) {
    this.notificationBody = notificationBody;
}
}

请帮忙!

Answer 1

好的，试试这个:

1) 将数组声明移出 onCreate() 方法，使其成为 Activity 的成员变量，这样您就不必将其声明为 final:

ArrayList<Word> words = new ArrayList<Word>();

2) 将适配器声明也添加为类的成员变量，并在访问数据库之前实例化适配器:

    adapter = new WordAdapter(this, words);
    ListView listView = findViewById(R.id.notification);
    listView.setAdapter(adapter);

3) 最后，将所有数据添加到列表后，调用 notifiyDatasetChanged() 适配器刷新列表。

for (DataSnapshot postSnapshot: dataSnapshot.getChildren()) {
                Word value = postSnapshot.getValue(Word.class);
                words.add(value);
                // TODO: handle the post
            }
 adapter.notifyDatasetChanged();