如何修复转到适配器中的下一个活动（在空对象引用上的Context.getPackageName（）'[重复]

Question

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在我的项目中，我通过改造工作并制作适配器和模型 问题，点击cardview后转到下一个活动，错误导致应用程序崩溃：

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
    at android.content.ComponentName.<init>(ComponentName.java:128)
    at android.content.Intent.<init>(Intent.java:5390)
    at ir.hmotamed.notline.adapter.NoteAdapter$1.onClick(NoteAdapter.java:54)
    at android.view.View.performClick(View.java:6261)

我的适配器代码：

public class NoteAdapter extends RecyclerView.Adapter<NoteAdapter.notesViewHoler> {


List<Querynotes> querynotes;
private Context mContext;

public NoteAdapter(List<Querynotes> querynotes, MainActivity mainActivity){

    this.querynotes=querynotes;

}

@NonNull
@Override
public notesViewHoler onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

    View view= LayoutInflater.from(parent.getContext()).inflate(R.layout.note_row,parent,false);
    return new notesViewHoler(view);

}

@Override
public void onBindViewHolder(@NonNull final notesViewHoler holder, int position) {

    final Querynotes queryPostses=querynotes.get(position);
    holder.title.setText(queryPostses.getTitle());
    holder.note.setText(queryPostses.getNote());
    holder.body.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Intent intent=new Intent(mContext,EditNoteActivity.class);
            intent.putExtra("nid",queryPostses.getId());
            intent.putExtra("ntitle",queryPostses.getTitle());
            intent.putExtra("ndesc",queryPostses.getNote());
            mContext.startActivity(intent);

        }
    });

}

@Override
public int getItemCount() {

    return querynotes.size();

}

public class notesViewHoler extends RecyclerView.ViewHolder{

    int id;
    CardView parent;
    TextView title;
    TextView note;
    RelativeLayout body;
    public notesViewHoler(View itemView) {
        super(itemView);
        parent=itemView.findViewById(R.id.rv_note_row);
        title=itemView.findViewById(R.id.tv_header_title);
        note=itemView.findViewById(R.id.tv_body_desc);
        body=itemView.findViewById(R.id.rv_row_body);

    }
}

我需要点击我的项目后转到下一个活动 但点击我的应用程序崩溃后，在我的适配器的第54行得到错误 第54行：

Intent intent=new Intent(mContext,EditNoteActivity.class);

Answer 1

你必须在使用之前初始化你的context：

public NoteAdapter(List<Querynotes> querynotes, MainActivity mainActivity){
mContext = mainActivity; \\ add this line
    this.querynotes=querynotes;

}

Answer 2

您的上下文为null因此崩溃。确保在适配器构造函数中传递上下文，如下所示：

public NoteAdapter(List<Querynotes> querynotes, Context mContext){

    this.querynotes=querynotes;
    this.mContext=mContext;

}

并在您创建适配器的活动中：

NoteAdapter mNoteAdapter = new NoteAdapter(queryNotes, MainActivity.class);