Question

尝试调用虚方法＆＃39; java.lang.String android.content.Context.getPackageName（）＆＃39;在空对象引用上

我知道这个问题在这里问了很多次，但我无法解决这个问题我是android新手，我无法解决这个问题

我想点击卡片视图并开始新的活动我为此编写代码，但问题是当我点击cardview时出现此错误

请告诉我如何解决这个问题

以下是我的代码

Maia活动

public class MainActivity extends AppCompatActivity {

private List<Data> movieList = new ArrayList<>();
private RecyclerView recyclerView;
private MoviesAdapter  mAdapter;
private Context context;

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

    recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
    mAdapter = new MoviesAdapter(movieList,context) ;
    context = getApplicationContext();

    RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
    recyclerView.setLayoutManager(mLayoutManager);
    recyclerView.setItemAnimator(new DefaultItemAnimator());
    recyclerView.setAdapter(mAdapter);

    prepareMovieData();
}

private void prepareMovieData() {

    Data data = new Data("MadMax");
    movieList.add(data);

    data = new Data("MadMax1");
    movieList.add(data);

    data = new Data("MadMax2");
    movieList.add(data);

    data = new Data("MadMax3");
    movieList.add(data);

    data = new Data("MadMax4");
    movieList.add(data);

    mAdapter.notifyDataSetChanged();
}
}

适配器

public class MoviesAdapter extends RecyclerView.Adapter<MoviesAdapter.MyViewHolder> {

private List<Data> moviesList;
private Context context;

@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View itemView = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.single_row_layout, parent, false);

    return new MyViewHolder(itemView);
}

public static class MyViewHolder extends RecyclerView.ViewHolder{
    public TextView title;

    public View view;
    public MyViewHolder(View v) {
        super(v);

        view = v;
        title = (TextView) view.findViewById(R.id.title);
    }
}

public MoviesAdapter(List<Data> moviesList,Context context) {

    this.moviesList = moviesList;
    this.context = context;
}

@Override
public void onBindViewHolder(MyViewHolder holder,int position) {

    Data data = moviesList.get(position);
    holder.title.setText(data.getTitle());

    holder.itemView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            Intent intent = new Intent(context,Parts.class);
            context.startActivity(intent);
        }
    });
}

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

logcat的

02-25 18：05：43.121 11930-11930 / com.example.owner.theconstitutionofindia E / AndroidRuntime：致命异议：主要过程：com.example.owner.theconstitutionofindia，PID：11930 java.lang.NullPointerException：尝试调用虚方法＆＃39; java.lang.String android.content.Context.getPackageName（）＆＃39;在null 对象参考在android.content.ComponentName。（ComponentName.java:77）在android.content.Intent。（Intent.java:4170）在 com.example.owner.theconstitutionofindia.MoviesAdapter $ 1.onClick（MoviesAdapter.java:86）在android.view.View.performClick（View.java:4785）在android.view.View $ PerformClick.run（View.java:19884）在android.os.Handler.handleCallback（Handler.java:739）在android.os.Handler.dispatchMessage（Handler.java:95）在android.os.Looper.loop（Looper.java:135）在android.app.ActivityThread.main（ActivityThread.java:5343） at java.lang.reflect.Method.invoke（Native Method）在java.lang.reflect.Method.invoke（Method.java:372）在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:905）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:700）

请告诉我如何解决此问题以及如何通过卡片视图开始新活动。

Answer 1

试试这个

context=MainActivity.this
mAdapter = new MoviesAdapter(movieList,context) ;

Answer 2

在您的代码中

mAdapter = new MoviesAdapter(movieList,context) ;
context = getApplicationContext();

您在初始化之前使用context。做到这一点

context = getApplicationContext();
mAdapter = new MoviesAdapter(movieList,context) ;

同时制作

context = getApplicationContext();

到

context = MainActivity.this;

Answer 3

首先检查两个文件是否在同一个包中，并将活动也传递给适配器。不要只传递上下文并将其投射到活动中。

public MoviesAdapter(List<Data> moviesList,Context context, Activity activity) {
this.moviesList = moviesList;
this.context = context;
this,activity = activity;
}

这种方法总是不起作用;

context = ActivityName.this;

＆＃39; java.lang.String android.content.Context.getPackageName（）＆＃39;在空对象引用

3 个答案: