Question

我一直在线跟踪一个示例，通过RecyclerView下载，解析和显示JSON内容。 Avaialble at：https://www.youtube.com/watch?v=SRmjXr6Ui-I

当我在模拟器上运行应用程序时，我收到错误代码。似乎无法弄清楚，我已经浏览了这个网站上的其他线程，但是我还没有能够解决我的问题。

我得到的错误代码是：

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setAdapter(android.support.v7.widget.RecyclerView$Adapter)' on a null object reference

错误发生在JSONparzer类的第62行。

是rv.setAdapter（new MyAdapter（c，users））;

 public class MainActivity extends AppCompatActivity {

    String jsonURL = "http://jsonplaceholder.typicode.com/users";

    public static final String TAG = "MainActivity";
    //FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);

    private RecyclerView rv;
    /*private ArrayList<Standing> mLeagueTable = new ArrayList<>(); //Initalise m
    private TableAdapter mTableAdapter = new TableAdapter(mLeagueTable, this); */

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

        rv = (RecyclerView) findViewById(R.id.rv);
        if (rv != null) {
            rv.setLayoutManager(new LinearLayoutManager(this));
        }
        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);   //Initialze FAB
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                new JSONDownloader(MainActivity.this, jsonURL, rv).execute();
            }
        });
    }
}



class JSONParzer extends AsyncTask<Void, Void, Boolean> {

    private Context c;
    private String jsonData;
    private RecyclerView rv;

    private ProgressDialog pd ;
    private ArrayList<User> users = new ArrayList<>();

    public JSONParzer(Context c, String jsonData, RecyclerView rv) {
        this.c = c;
        this.jsonData = jsonData;
        this.rv = rv;
    }


    @Override
    protected void onPreExecute() {
        super.onPreExecute();

        pd = new ProgressDialog(c);
        pd.setTitle("Parse");
        pd.setMessage("Parsing..Please Wait");
        pd.show();
    }

    @Override
    protected Boolean doInBackground(Void... params) {

        return parse();
    }

    @Override
    protected void onPostExecute(Boolean isParsed) {
        super.onPostExecute(isParsed);

        pd.dismiss();   //Dismiss progress dialog.
        if (isParsed)
        {
            //BIND(using the adapters)
            rv.setAdapter(new MyAdapter(c, users));   //Pass in instance of adapter.

        } else
        {
            Toast.makeText(c, "Unable to Parse check your Log Output", Toast.LENGTH_SHORT).show();
        }
    }

    private Boolean parse()
    {
        try {
            JSONArray ja = new JSONArray(jsonData);
            JSONObject jo;  //declare json OBJECT

            users.clear();
            User user;

            for (int i=0; i< ja.length(); i++)  //iterating in JSONArray
            {
                jo = ja.getJSONObject(i);
                String name = jo.getString("name");
                String username = jo.getString("username");
                String email = jo.getString("email");

                user = new User();      //Create a new "User" object.

                user.setName(name);
                user.setUsername(username);
                user.setEmail(email);

                users.add(user);    //Add new user object to ArrayList users.
            }
            return true;

        } catch (JSONException e) {
            e.printStackTrace();
            return false;
        }
    }


}

错误发生在JSONParzer类的第62行。

我也会在下面包含布局文件。

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="16dp"
    android:paddingLeft="16dp"
    android:paddingRight="16dp"
    android:paddingTop="16dp"
   tools:context=".UI.MainActivity"
    tools:showIn="@layout/activity_main"  >
content_main

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

    </android.support.v7.widget.RecyclerView>


</RelativeLayout>

activity_main

<?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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    tools:context="com.example.oisin.premierleaguesocial.UI.MainActivity"
    android:weightSum="1">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/app_name"
        android:id="@+id/test"
        android:textAppearance="@style/TextAppearance.AppCompat.Display1" />


    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignEnd="@+id/test"
        android:layout_alignParentBottom="true"
        android:layout_alignRight="@+id/test"
        android:clickable="true"
        app:fabSize="mini"
        app:srcCompat="@android:drawable/presence_online" />

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:background="?attr/colorPrimary"
        android:contentInsetStart="0dp"
        android:contentInsetLeft="0dp"
        app:contentInsetLeft="0dp"
        app:contentInsetStart="0dp"
        app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light"/>


</RelativeLayout>

非常感谢任何帮助。谢谢你的时间。

Answer 1

发生崩溃是因为android系统无法从“activity_main.xml”中找到回收站视图。

请尝试添加以下代码“activity_main.xml”布局：

curl -X POST -H "Jenkins-Crumb:${JENKINS_CRUMB}" http://${JENKINS_URL}/job/${JOB_NAME}/${BUILD_ID}/input/${INPUT_ID}/abort

因此改变后的布局将是：

<android.support.v7.widget.RecyclerView
    android:id="@+id/rv"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
</android.support.v7.widget.RecyclerView>

Answer 2

RecyclerView XML中没有activity_main，导致NullPointerException。

将RecyclerView添加到activity_main，然后重试。

<?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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    tools:context="com.example.oisin.premierleaguesocial.UI.MainActivity"
    android:weightSum="1">

    ................
    .........................


     <android.support.v7.widget.RecyclerView
        android:id="@+id/rv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

    </android.support.v7.widget.RecyclerView>

</RelativeLayout>

使用RecyclerView时应用程序崩溃

2 个答案: