适配器中的Android上下文操作栏？

Question

我试图在我的应用程序中实现上下文操作栏。 但是，当我尝试在适配器中使用Startactionmode方法时，找不到任何方法。

我努力了 ：

mActionMode = ((MainActivity)c).startActionMode(new MyActionModeCallback());

这给我一个错误

java.lang.NullPointerException：尝试在CustomerListAdapter $ ViewHolder $ 1.onClick（CustomerListAdapter.java:62）上调用虚拟方法'

java：62是

mActionMode = ((MainActivity)c).startActionMode(new MyActionModeCallback());

顺便说一句，我正在导入import android.view.ActionMode; 及其在mainactivity工具中的tabs片段实现actionbaractivity

我的适配器类

public class CustomerListAdapter extends RecyclerView.Adapter<CustomerListAdapter.ViewHolder>{

public ViewHolder(final View itemView,int ViewType, final Context c) {   

然后我设定

itemView.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {

                mActionMode = ((MainActivity)c).startActionMode(new MyActionModeCallback());
            }
        }); 

我的适配器代码如下

    package com.thecueapps.cue_business;

    import android.content.Context;
    import android.support.v7.widget.CardView;
    import android.support.v7.widget.RecyclerView;
    import android.view.ActionMode;
    import android.view.LayoutInflater;
    import android.view.Menu;
    import android.view.MenuItem;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ImageView;
    import android.widget.TextView;

    import com.parse.ParseUser;

    import java.text.ParseException;
    import java.text.SimpleDateFormat;
    import java.util.Date;
    import java.util.List;


    public class CustomerListAdapter extends RecyclerView.Adapter<CustomerListAdapter.ViewHolder>{
    protected List<ParseUser> mCustomers;

    Context context;
    public static class ViewHolder extends RecyclerView.ViewHolder {

        TextView Name_fiedl;
        TextView Number_ppl_field;
        TextView Time_field;
        Context contxt;
        Context contxt1;
        private CardView cardView;
        private ImageView circleview;
        public ActionMode mActionMode;




        public ViewHolder(final View itemView,int ViewType, final Context c) {                 // Creating ViewHolder Constructor with View and viewType As a parameter
            super(itemView);
            contxt = c;

            //itemView.setClickable(true);
            //itemView.setOnClickListener(this);
            // Here we set the appropriate view in accordance with the the view type as passed when the holder object is created
            Name_fiedl = (TextView) itemView.findViewById(R.id.text_name); // Creating TextView object with the id of textView from item_row.xml
            Number_ppl_field = (TextView) itemView.findViewById(R.id.number_ppl);// Creating ImageView object with the id of ImageView from item_row.xml
            circleview=(ImageView) itemView.findViewById(R.id.circle_ppl);
            Time_field=(TextView) itemView.findViewById(R.id.text_time);

            itemView.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                   /* Toast.makeText(itemView.getContext(), "hi "
                            , Toast.LENGTH_SHORT).show();*/


    mActionMode = ((MainActivity)c).startActionMode(new       MyActionModeCallback());

                }
            });

            //Add Expand Area to a Card
            cardView = (CardView) itemView.findViewById(R.id.card_view);
            cardView.setRadius(0);

        }



    }



        CustomerListAdapter(List<ParseUser> customer){ // MyAdapter Constructor with titles and icons parameter
        // titles, icons, name, email, profile pic are passed from the main activity as we
       mCustomers=customer;



        //in adapter
    }



    @Override
    public CustomerListAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_row,parent,false); //Inflating the layout

            ViewHolder vhItem = new ViewHolder(v,viewType,context); //Creating ViewHolder and passing the object of type view

            return vhItem; // Returning the created object

            //inflate your layout and pass it to view holder
    }

    @Override
    public void onBindViewHolder(CustomerListAdapter.ViewHolder holder, int position) {

        ParseUser  customer=mCustomers.get(position);
        holder.Name_fiedl.setText(customer.getString(ParseConstants.KEY_USER_REAL_NAME)); // Setting the Text with the array of our Titles
        holder.Number_ppl_field.setText(String.valueOf(customer.getInt(ParseConstants.KEY_CUSTOMER_NUMBER_PPL)));// Settimg the image with array of our icons
        String time=customer.getString(ParseConstants.KEY_CUSTOMER_TIME);
        SimpleDateFormat dateFormat = new SimpleDateFormat("MM/dd/yyyy h:mm:ss a");
        SimpleDateFormat dateFormat2 = new SimpleDateFormat("hh:mm aa");
        try {
            Date date = dateFormat.parse(time);

             String out= dateFormat2.format(date);
            holder.Time_field.setText(out);
            //Log.e("Time", out);
        } catch (ParseException e) {
        }


        if(customer.getInt(ParseConstants.KEY_CUSTOMER_NUMBER_PPL)==3){
            holder.circleview.setImageResource(R.color.lightblue500);
        }
        else if(customer.getInt(ParseConstants.KEY_CUSTOMER_NUMBER_PPL)==4){
            holder.circleview.setImageResource(R.color.lightblue500);
        }
        else if(customer.getInt(ParseConstants.KEY_CUSTOMER_NUMBER_PPL)==5){
            holder.circleview.setImageResource(R.color.lightgreen500);
        }
        else if(customer.getInt(ParseConstants.KEY_CUSTOMER_NUMBER_PPL)>5){
            holder.circleview.setImageResource(R.color.lightgreen500);
        }

    }
    @Override
    public int getItemCount() {

        return mCustomers.size(); // the number of items in the list will be +1 the titles including the header view.
    }
    public void remove(String item) {
        int position = mCustomers.indexOf(item);
        mCustomers.remove(position);
        notifyItemRemoved(position);
    }
   }

class MyActionModeCallback implements ActionMode.Callback{


    @Override
    public boolean onCreateActionMode(ActionMode actionMode, Menu menu) {
        actionMode.getMenuInflater().inflate(R.menu.menu_login, menu);
        return false;
    }

    @Override
    public boolean onPrepareActionMode(ActionMode actionMode, Menu menu) {
        actionMode.setTitle("hihi");
        return false;
    }

    @Override
    public boolean onActionItemClicked(ActionMode actionMode, MenuItem menuItem) {
        return false;
    }

    @Override
    public void onDestroyActionMode(ActionMode actionMode) {

    }
}

因为我的适配器在片段内。 这是我尝试过并且仍然面临的问题。

1. 在我的片段中：

    mAdapter = new CustomerListAdapter(mCustomers, getActivity()); 

2. 在我的适配器中：

    CustomerListAdapter(List < ParseUser > customer, Activity Activity) { // MyAdapter Constructor with titles and icons parameter // titles, icons, name, email, profile pic are passed from the main activity as we mCustomers = customer; mActivity= Activity; //in adapter } 

3. 对于我的onclicklistener：

   itemView.setOnClickListener（new View.OnClickListener（）{public void onClick（View v）{

     mActionMode = mActivity.startActionMode(new MyActionModeCallback()); } }); 

但是我仍然面临显示非静态字段的错误，不能应用于静态字段吗？

Answer 1

这里：

mActionMode = ((MainActivity)c).startActionMode(new MyActionModeCallback());

Context的c对象可能为null。

要在CustomerListAdapter类中获取活动上下文，请使用类构造函数：

private Acivity mActivity;

public CustomerListAdapter(Activity mActivity){
  this.mActivity=mActivity;
  ....
}

使用mActivity从Activity调用startActionMode方法：

 mActionMode = mActivity.startActionMode(new MyActionModeCallback());

而从MainActivity传活动上下文使用this创建时CustomerListAdapter类对象：

CustomerListAdapter adapter=new CustomerListAdapter(this);

Answer 2

活动中

 public class Main extends AppCompatActivity {
     public Toolbar toolbar;
    AdapterEXT mAdapter;
    .....
     @Override
        protected void onCreate(Bundle savedInstanceState) {
     toolbar = (Toolbar) findViewById(R.id.toolbar);
            setSupportActionBar(toolbar);
            assert getSupportActionBar() != null;
            getSupportActionBar().setDisplayHomeAsUpEnabled(true);
            getSupportActionBar().setDisplayShowHomeEnabled(true);
    ......
     List<DataXXX> data = new ArrayList<>();
     mAdapter = new AdapterEXT(Main.this , toolbar, data);

在适配器中

 class AdapterEXT extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
        public Context context;
        public Toolbar toolbar;
     AdapterEXT (Context context, Toolbar toolbar, List<DataXXX> dataXXX) {
             this.context = context;
            this.toolbar=toolbar;
            this.dataXXX = dataXXX;
        }

您想要在适配器中的位置

toolbar.setTitle(context.getString(R.string.YourTXTfromXML));