如何使用适配器在 Android ListView 中显示 Firestore 集合

Question

我正在开发一个简单的应用程序，我需要在我的应用程序中查看特定 FirebaseFirestore 集合中的每个文档。

为了完成这项工作，我认为最好的解决方案是使用 ListView 和自定义 ArrayAdapter。并将 Firestore 文档转换为我制作的自定义 java 类。

我的文档设置为：

（字符串）标题：

（日期）到期日期：

（数字）exp：

（字符串）描述：

但是，我的逻辑中的某些东西似乎不起作用。下面是我的这个过程的代码：

Missions.java：

public class Missions {

    private String title;
    private Number exp;
    private String date;
    private String description;

    public Missions() {}

    public Missions(String title, Number exp, String date, String description) {
        this.title = title;
        this.exp = exp;
        this.date = date;
        this.description = description;
    }

    public String getTitle(){
        return title;
    }
    public Number getExp(){
       return exp;
    }
    public String getDate(){
        return date;
    }
    public String getDescription(){
        return description;
   }

}

MainActivity.java：

    public class MainActivity extends AppCompatActivity {
      private final String COLLECTION_KEY = "missions";

      //Views
      private TextView mHeaderView;
      private ListView mMissionListView;

      //Firebase
      private FirebaseFirestore db;

      //Adapter
      private MissionsAdapter mMissionAdapter;
      private ArrayList<Missions> mMissionsList;

      @Override
      protected void onCreate(Bundle savedInstanceState){
        /*
         * My code here deals with authentication
         *
         */
         super.onCreate(savedInstanceState);

         setContentView(R.layout.activity_main);

         mHeaderView = (TextView) findViewById(R.id.missionHeader);
         mMissionsListView = (ListView) findViewById(R.id.missionList);

         mHeaderView.setText("Available Missions"));

    //get Database
         db = FirebaseFirestore.getInstance();
    //Set up the ArrayList
         mMissionsList = new ArrayList<Missions>();
    //set the Adapter
        mMissionAdapter = new MissionsAdapter(this, mMissionsList);

        mMissionListView.setAdapter(mMissionAdapter);

        db.collection(COLLECTION_KEY).get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                        @Override
                        public void onComplete(@NonNull Task<QuerySnapshot> task) {
                            if(task.isSuccessful()){
                                for(QueryDocumentSnapshot document : task.getResult()){

                                    Log.d("MissionActivity", document.getId() + " => " + document.getData());

                                    Missions miss = document.toObject(Missions.class);
                                    mMissionsList.add(miss);

                                }

                            }
                            else {
                                Log.d("MissionActivity", "Error getting documents: ", task.getException());
                            }
                        }
                    });
        //add the whole Arraylist of MIssions to the adapter
        mMissionAdapter.addAll(mMissionsList);
      }
    }

MissionsAdapter.java

    import android.app.Activity;
    import android.content.Context;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ArrayAdapter;
    import android.widget.TextView;

    import java.util.List;



    public class MissionsAdapter extends ArrayAdapter<Missions> {
        public MissionsAdapter(Context context, List<Missions> object){
            super(context,0, object);
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent){
            if(convertView == null){
                convertView =  ((Activity)getContext()).getLayoutInflater().inflate(R.layout.item_mission,parent,false);
            }

            TextView titleTextView = (TextView) convertView.findViewById(R.id.mission_title);
            TextView expTextView = (TextView) convertView.findViewById(R.id.mission_exp);
            TextView dateTextView = (TextView) convertView.findViewById(R.id.mission_date);
            TextView descriptionTextView = (TextView) convertView.findViewById(R.id.mission_description);

            Missions mission = getItem(position);

            titleTextView.setText(mission.getTitle());
            expTextView.setText(mission.getExp().toString());
            dateTextView.setText(mission.getDate());
            descriptionTextView.setText(mission.getDescription());


            return convertView;
        }

    }

item_missions.xml

    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:padding="16dp">

        <TextView
            android:id="@+id/mission_title"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:fontFamily="sans-serif-medium"
            android:textAppearance="?android:textAppearanceMedium"
            android:textColor="@color/input_login"
            android:hint="There will be a title"/>

        <TextView
            android:id="@+id/mission_exp"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:fontFamily="sans-serif"
            android:textAppearance="?android:textAppearance"
            android:textColor="@color/input_login"
            android:hint="There will be exp"/>

        <TextView
            android:id="@+id/mission_date"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:fontFamily="sans-serif"
            android:textAppearance="?android:textAppearance"
            android:textColor="@color/input_login"
            android:hint="There will be a date"/>

        <TextView
            android:id="@+id/mission_description"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:fontFamily="sans-serif"
            android:textAppearance="?android:textAppearance"
            android:textColor="@color/input_login"
            android:hint="There will be a description"/>

    </LinearLayout>

activity_main.xml

    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView
            android:id="@+id/missionHeader"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Edit/Create mission"
            android:gravity="center"
            android:textStyle="bold"
            android:textColor="@android:color/black"
            android:textAllCaps="true"
            android:textSize="30dp"
            android:paddingTop="20dp"
            />


        <ListView
            android:id="@+id/missionList"
            android:layout_width="match_parent"
            android:layout_height="match_parent">

        </ListView>


    </LinearLayout>

任何评论都会有所帮助。

Answer 1

你快到了。您的代码中的问题是您尝试使用空列表填充适配器，这是因为在您执行此操作时，您还没有完成从数据库中获取数据。请注意，onComplete() 方法具有异步行为。要解决这个问题，请使用以下代码：

db.collection(COLLECTION_KEY).get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<QuerySnapshot> task) {
        List<Missions> mMissionsList = new ArrayList<>();
        if(task.isSuccessful()){
            for(QueryDocumentSnapshot document : task.getResult()) {
                Missions miss = document.toObject(Missions.class);
                mMissionsList.add(miss);
            }
            ListView mMissionsListView = (ListView) findViewById(R.id.missionList);
            MissionsAdapter mMissionAdapter = new MissionsAdapter(this, mMissionsList);
            mMissionsListView.setAdapter(mMissionAdapter);
        } else {
            Log.d("MissionActivity", "Error getting documents: ", task.getException());
        }
    }
});

如你所见，我已经在这个方法中声明并使用了适配器。