Question

我是Android开发的初学者，正在开发一个小项目，以显示设备上现有传感器的列表。但我可以显示传感器列表。我调试了，当我运行程序时，我发现有18个传感器，但我无法在Android屏幕上显示它们。

listItem.java代码：

    public class ListItem {
    private String title;

    public ListItem(String title) {
        this.title = title;
    }

    public String getTitle() {
        return title;
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity {
    private RecyclerView recyclerView;
    private RecyclerView.Adapter adapter;
    private List<ListItem>  SensorItems;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        recyclerView = (RecyclerView) findViewById(R.id.sensorsRV);
        SensorItems = new ArrayList<ListItem>();

        SensorManager sensorManager = (SensorManager) this.getSystemService(this.SENSOR_SERVICE);
        List sensorList = sensorManager.getSensorList(Sensor.TYPE_ALL);

        for(int i = 0; i < sensorList.size(); i++){
            ListItem currentSensor = new ListItem(((Sensor)(sensorList.get(i))).getName());
            SensorItems.add(currentSensor);
        }
        adapter = new MyAdapter(SensorItems);
        recyclerView.setAdapter(adapter);
    }


}

MyAdapter.java

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
    List <ListItem> listItems;
    private Context context;

    public MyAdapter(List<ListItem> listItems) {
        this.listItems = listItems;

    }

    //creates whenever our view holder is created
    @Override
    public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item,parent,false);
        return new ViewHolder(view);

    }

    //this method is called after onCreateViewHolder to bind data to view holder to show actuall data to recycler view
    @Override
    public void onBindViewHolder(MyAdapter.ViewHolder holder, int position) {
        ListItem listItem = listItems.get(position);
        holder.headingTextView.setText(listItem.getTitle());
    }

    @Override
    public int getItemCount() {
        return listItems.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder{
        public TextView headingTextView;
        Context context;
        public LinearLayout myLayout;


        public ViewHolder(View itemView) {
            super(itemView);
            myLayout = (LinearLayout) itemView;
            headingTextView = (TextView) itemView.findViewById(R.id.textVeiwHead);
            context = itemView.getContext();
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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"
    tools:context="com.example.sahar.devicesensors.MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_margin="30dp"
            android:text="List of Device's Sensors"
            android:textSize="16dp"
            android:textStyle="bold"
            android:textColor="@android:color/holo_blue_dark"/>


        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">

            <android.support.v7.widget.RecyclerView
                android:id="@+id/sensorsRV"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:padding="20dp" />
        </LinearLayout>
    </LinearLayout>
</android.support.constraint.ConstraintLayout>

list_item.xml

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

            <LinearLayout
                android:padding="20dp"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="vertical">
                    <TextView
                        android:id="@+id/textVeiwHead"
                        android:text="Heading"
                        android:textAppearance="@style/Base.TextAppearance.AppCompat.Large"
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content" />
            </LinearLayout>

</android.support.constraint.ConstraintLayout>

如果有人可以给我一些提示，为什么我无法获得列表显示我真的很感激。

Answer 1

在MainActivity上试试这个：

recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(new LinearLayoutManager(this));

LayoutManager的构造函数接收上下文。 Context包含有关应用程序的全局信息。

活动从Context扩展，因此您可以使用活动。

Answer 2

在将数据显示到回收站视图后，对主要活动进行一些更改。

   public class MainActivity extends AppCompatActivity {

        private RecyclerView recyclerView;
        private MyAdapter adapter;
        private List<ListItem> SensorItems;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            recyclerView = (RecyclerView) findViewById(R.id.sensorsRV);

            recyclerView.setLayoutManager(new LinearLayoutManager(this));
            SensorItems = new ArrayList<ListItem>();

            SensorManager sensorManager = (SensorManager) this.getSystemService(this.SENSOR_SERVICE);
            List sensorList = sensorManager.getSensorList(Sensor.TYPE_ALL);

            for (int i = 0; i < sensorList.size(); i++) {
                ListItem currentSensor = new ListItem(((Sensor) (sensorList.get(i))).getName());
                SensorItems.add(currentSensor);
            }
            adapter = new MyAdapter(SensorItems);
            recyclerView.setAdapter(adapter);
            adapter.notifyDataSetChanged();
        }

    }

Answer 3

RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(mContext);
    recyclerView.setLayoutManager(layoutManager);

继续setAdapter。

Answer 4

setAdapter

您必须在LayoutManager之前wrap_content，因为适配器取决于layout_height。并且，您最好在list_item.xml的根节点中使用~(\.png|gif|jpe?g|bmp)$~ if (preg_match('~(\.png|gif|jpe?g|bmp)$', $data->files)) { echo 'image only;' } else { echo 'image + other types'; }。

Answer 5

我发现您没有在回收站视图中设置布局管理器。所以您可以通过xml设置布局管理器，如下所示： -

<android.support.v7.widget.RecyclerView
    xmlns:app="http://schemas.android.com/apk/res-auto"
    app:layoutManager="android.support.v7.widget.LinearLayoutManager" >

或者您也可以使用以下代码执行上述操作： -

//To show vertical scrolling list
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(linearLayoutManager);

//To show horizontal scrolling list
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
recyclerView.setLayoutManager(linearLayoutManager);

Android：我的回收站视图不显示列表

5 个答案: