使用意图从适配器将用户发送到另一个活动。

Question

我试图在收集位置后，当用户点击回收视图内的图片时，将其发送到另一个活动，问题是无论我做什么，当使用上下文时，我仍然在Adapter上得到null，请找到下面的代码，并向我描述我错过了什么？

问题出在onclick方法的代码里（最后一个）：----。

package com.example.boc.Teachers;

import androidx.appcompat.app.AppCompatActivity;
import androidx.cardview.widget.CardView;
import androidx.recyclerview.widget.RecyclerView;

import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import com.example.boc.R;
import com.example.boc.main.DashboardActivity;

import java.util.ArrayList;

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

    private LayoutInflater mInflater;
    private ArrayList<TeachersModel> items;
    private TeacherMain mActivity;
    private Context context;
    public TeachersAdapter(ArrayList<TeachersModel> data, TeacherMain activity) {
        this.items = data;
        this.mActivity = activity;
        this.mInflater = LayoutInflater.from(mActivity);
    }

    public void addItem(TeachersModel result) {
        items.add(result);
    }
    public TeachersAdapter(Context context) {
        this.context = context;
    }
    public void setInflater(LayoutInflater layoutInflater){
        this.mInflater =layoutInflater;
    }

    public void replaceItems(ArrayList<TeachersModel> newItems) {
        this.items.clear();
        for(TeachersModel item: newItems)
            this.items.add(item);
    }

    public void insertItem(TeachersModel item) {
        items.add(0, item);
    }

    public void clearItems(){
        items.clear();
    }

    public void AddResults(ArrayList<TeachersModel> result) {
        items.addAll(result);
    }

    public TeachersModel getItemsAt(int position){
        return  items.get(position);
    }

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

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        TeachersModel model = items.get(position);
        MessageViewHolder messageViewHolder = (MessageViewHolder) holder;
        messageViewHolder.imageViewIcon.setBackgroundResource(model.getImage());
        messageViewHolder.textViewName.setText(model.getName());
        messageViewHolder.textViewStatus.setText(model.getStatus());
        messageViewHolder.textViewMobile.setText(model.getMobile());
    }

    @Override
    public int getItemViewType(int position) {
        return  super.getItemViewType(position);
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View rootCategoryView = mInflater.inflate(R.layout.row_item_teachers, parent, false);
        return new MessageViewHolder(rootCategoryView, this);
    }

    private class MessageViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

        private ImageView imageViewIcon;
        private TextView textViewName;
        private TextView textViewStatus;
        private TextView textViewMobile;
        private CardView cardView;

        private MessageViewHolder(View itemView, TeachersAdapter adapter) {
            super(itemView);
            imageViewIcon = (ImageView) itemView.findViewById(R.id.imageViewIcon);
            textViewName = (TextView) itemView.findViewById(R.id.textViewName);
            textViewStatus = (TextView) itemView.findViewById(R.id.textViewStatus);
            textViewMobile = (TextView) itemView.findViewById(R.id.textViewMobile);
            cardView = (CardView) itemView.findViewById(R.id.cardView);

            cardView.setOnClickListener(this);
        }

        @Override
        public void onClick(View v) {
            final int pos = getAdapterPosition();
            if (pos == 0) {
                imageViewIcon.setOnClickListener( new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        Intent intent = new Intent( context, DashboardActivity.class );
                        context.startActivity( intent );
                    }
                } );

                Toast.makeText(mActivity, "Selected Item Position "+pos, Toast.LENGTH_SHORT).show();
            }
        }
    }
}

Answer 1

我假设你使用的是 constrcutor 顺理成章 context:

//update the constructor to take a context

public TeachersAdapter(ArrayList<TeachersModel> data, TeacherMain activity , Context context) {
this.items = data;
this.mActivity = activity;
this.mInflater = LayoutInflater.from(mActivity);
//add this
this.context = context;
}

设置点击监听器在 onBindViewHolder:

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

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

messageViewHolder.imageViewIcon.setOnClickListener( new View.OnClickListener() {

@Override
public void onClick(View view) {

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

}

当您创建 adapter 在你的活动中，请确保通过正确的 context:

adapter = new TeachersAdapter(... , .... ,  getApplicationContext());