Question

我在ListView中有一个NestedScrollView。当我将Firebase中的项目加载到列表中时，屏幕上不会显示任何内容。我认为它不会调用getview方法，否则它至少会显示我设置为自定义布局的默认图像。

当我打印结果时，查询似乎工作正常。

任何帮助？

public class ListAnimalsByHabitatActivity extends AppCompatActivity {

private ListView listView;
private ArrayList<Animal> list = new ArrayList<Animal>();
private String habitat;
private ImageView cover;
private TextView Habitat_name;

FirebaseFirestore db = FirebaseFirestore.getInstance();


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list_animals_by_habitat);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);


    listView = (ListView) findViewById(R.id.animal_list_view);
    cover = (ImageView) findViewById(R.id.coverimage);
    Habitat_name = (TextView) findViewById(R.id.habitatname);

    Intent i = getIntent();
    habitat = i.getStringExtra("habitat");
    String s = i.getStringExtra("cover");
    String habitat_name = i.getStringExtra("habitat_name");

    Habitat_name.setText(habitat_name);
    Glide.with(this).load(s).into(cover);


    MyTasks mt = new MyTasks();
    mt.execute();

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            Intent i = new Intent(getApplicationContext(), AnimalViewerActivity.class);
            i.putExtra("type", list.get(position).getType());
            startActivity(i);
        }
    });

}

class MyTasks extends AsyncTask{

    @Override
    protected Object doInBackground(Object[] objects) {
        db.collection("Animal")
                .whereEqualTo("Habitat", habitat)
                .get()
                .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {
                        if (task.isSuccessful()) {
                            for (QueryDocumentSnapshot document : task.getResult()) {
                                String pic = document.getData().get("Picture").toString();
                                String name = document.getData().get("Name").toString();
                                String type = document.getData().get("Type").toString();
                                String desc = document.getData().get("Description").toString();
                                list.add(new Animal(habitat, type, name, pic, type));
                            }
                        } else {

                        }
                    }
                });

        return null;
    }

    @Override
    protected void onPostExecute(Object o) {
        MyNewCustomAdapter ca = new MyNewCustomAdapter(getApplicationContext(), list);
        listView.setAdapter(ca);
    }
}

class MyNewCustomAdapter extends ArrayAdapter<Animal>{
    private Context mContext;
    private ArrayList<Animal> array;
    public MyNewCustomAdapter(Context context, ArrayList<Animal> array) {
        super(context, -1, array);
    }

    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        LayoutInflater layoutInflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View rowview = layoutInflater.inflate(R.layout.petite_list_animal_layout, parent, false);
        ImageView im = rowview.findViewById(R.id.IMAGE);
        Glide.with(getApplicationContext()).load(list.get(position).getPicture()).into(im);
        return rowview;
    }
}

@Override
public void finish() {
    super.finish();
    overridePendingTransition(R.anim.slide_in_left, R.anim.slide_out_right);
}

}

这是xml文件

<?xml version="1.0" encoding="utf-8"?>

<android.support.design.widget.CoordinatorLayout 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:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/background_light"
android:fitsSystemWindows="true">

<android.support.design.widget.AppBarLayout
    android:id="@+id/main.appbar"
    android:layout_width="match_parent"
    android:layout_height="300dp"
    android:fitsSystemWindows="true"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

    <android.support.design.widget.CollapsingToolbarLayout
        android:id="@+id/main.collapsing"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="true"
        app:contentScrim="?attr/colorPrimary"
        app:expandedTitleMarginEnd="64dp"
        app:expandedTitleMarginStart="48dp"
        app:layout_scrollFlags="scroll|snap">

        <ImageView
            android:id="@+id/coverimage"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:fitsSystemWindows="true"
            android:scaleType="centerCrop"
            android:src="@drawable/ic_launcher_background"
            app:layout_collapseMode="parallax" />

        <android.support.v7.widget.Toolbar
            android:id="@+id/main.toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            app:layout_collapseMode="pin"
            app:layout_scrollFlags="scroll|snap"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

        <TextView
            android:id="@+id/habitatname"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="250dp"
            android:paddingLeft="20dp"
            android:text="Habitat Name"
            android:textColor="@android:color/white"
            android:textSize="22dp"
            android:textStyle="bold" />

    </android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>

<android.support.v4.widget.NestedScrollView
    android:id="@+id/nestedScrollView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fillViewport="true"
    app:layout_behavior="@string/appbar_scrolling_view_behavior">


    <ListView
        android:id="@+id/animal_list_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="20dp">

    </ListView>


</android.support.v4.widget.NestedScrollView>

Answer 1

Firebase数据库客户端已在后台线程中运行所有网络操作。这意味着所有操作都可以在不阻塞主线程的情况下进行。将它放在AsyncTask中并没有带来任何额外的好处。

要解决此问题，只需在onCreate()方法中使用以下代码行：

db.collection("Animal")
            .whereEqualTo("Habitat", habitat)
            .get()
            .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                @Override
                public void onComplete(@NonNull Task<QuerySnapshot> task) {
                    if (task.isSuccessful()) {
                        for (QueryDocumentSnapshot document : task.getResult()) {
                            String pic = document.getData().get("Picture").toString();
                            String name = document.getData().get("Name").toString();
                            String type = document.getData().get("Type").toString();
                            String desc = document.getData().get("Description").toString();
                            list.add(new Animal(habitat, type, name, pic, type));
                        }
                    } else {

                    }
                }
            });

请记住，由于其异步行为，仅在list方法内定义和使用onComplete()。如果您想使用list onComplete()外ttl方法，我建议您从 post 中查看我的anwser的最后一部分，并查看此内容的 video

Listview没有显示项目（使用自定义适配器）

1 个答案: