如何连接我的ListAdapter类，使其在具有针对行的自定义“模型”类的片段中工作？

Question

I am trying to create a customized ListView in an app I am making following a tutorial. The tutorial works fine if you want to launch the ListView from an activity, but I am trying to get it to work from inside a fragment and I can not seem to figure out how to connect my adapter to the fragment. Does anyone know how I could figure this out? Kotlin is quite new to me at this point, so there might be an obvious solution, I just have not found it yet.

I did get it to work attaching the code to an activity, but in my project, I am trying to attach it to a fragment in a navigation bar, but the fragment will not handle the code that is working in the activity.

This is what the code looks like in the onCreate-method when it is attached to an activity:

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        //listview
        var listView = findViewById<ListView>(R.id.listView)

        var list = mutableListOf<Model>()

        //adding items to the listview
        list.add(Model("title one", "description one....", R.drawable.imgone))
        list.add(Model("title two", "description two....", R.drawable.imgtwo))
.....

        //adapter
        listView.adapter = MyListAdapter(this, R.layout.row, list)

        //ListView item clicks
        listView.setOnItemClickListener { parent, view, position, id ->
            if (position == 0){
                Toast.makeText(this@MainActivity, "Item One clicked", Toast.LENGTH_LONG).show()
            }
            if (position == 1){
                Toast.makeText(this@MainActivity, "Item Two clicked", Toast.LENGTH_LONG).show()
            }
.....
        }

    }

This is what the code looks like in the fragment at this point

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val view = inflater.inflate(R.layout.fragment_home, container, false)

        val listView: ListView = view.findViewById(R.id.homeListView)

        val adapter: MyListAdapter
        //Not sure how to instantiate MyListAdapter

        return view
    }

The Model class looks like this

class Model(val title: String, val desc: String, val img: Int)

And MyListAdapter looks like this

class MyListAdapter (var mCtx: Context, var resource: Int, var items: List<Model>)
    :ArrayAdapter<Model>(mCtx, resource, items){


    override fun getView(position: Int, convertView: View?, parent: ViewGroup): View {

        val layoutInflater: LayoutInflater = LayoutInflater.from(mCtx)

        val view: View = layoutInflater.inflate(resource, null)
        val imageView: ImageView = view.findViewById(R.id.list_view_image)
        val titleView: TextView = view.findViewById(R.id.list_view_title_txt)
        val descTView: TextView = view.findViewById(R.id.list_view_desc_txt)

        var mItems: Model = items[position]

        imageView.setImageDrawable(mCtx.resources.getDrawable(mItems.img))
        titleView.text = mItems.title
        descTView.text = mItems.desc


        return view
    }
}

My fragment_home.xml uses a pretty simple ListView:

<ListView
            android:id="@+id/homeListView"
            android:layout_width="match_parent"
            android:layout_height="match_parent">

    </ListView>

Whilst it is the row.xml that customizes the look of the items in my list

<LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:padding="10dp">

    <ImageView
            android:id="@+id/list_view_image"
            android:layout_width="80dp"
            android:layout_height="80dp"
            android:contentDescription="@string/list_view_img_content_desc"/>

    <LinearLayout
            android:layout_margin="5dp"
            android:layout_gravity="center"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical">

        <TextView
                android:id="@+id/list_view_title_txt"
                android:text="@string/list_view_title"
                android:textSize="15sp"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"/>
        <TextView
                android:id="@+id/list_view_desc_txt"
                android:text="@string/list_view_desc"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"/>

    </LinearLayout>

</LinearLayout>

What it is supposed to do, is that I should be able to launch my customized ListView from my HomeFragment and from there be able to click on an item in the list and have a Toast show up(eventually another fragment, but first things first). At the moment, I have the customized rows and the ListView ready, but I can not seem to make the connection from MyListAdapter to the HomeFragment.

Answer 1

MyListAdapter should be able to take a reference to a Fragment instead of a Context (Activity) provided you change the parameter type and local variable in MyListAdapter, then, you just have to pass 'this' and the syntax is the same as that of an Activity. If that doesn't work, then you might need to get the Fragment's Context (Activity) onCreate() and save it for use in the creation of MyListAdapter. I'll have to look at my code samples tomorrow for an example...

OK, this is how I do it (sorry it is not in Kotlin):

FavoritesFragment.java

            package org.mycompany.myapp;

            import java.util.ArrayList;
            import java.util.HashMap;
            import java.util.Map;

            import org.json.JSONArray;
            import org.json.JSONException;
            import org.json.JSONObject;
            import org.mycompany.TEST.adapter.FavoriteListAdapter;
            import org.mycompany.TEST.model.FavoriteItem;

            import android.app.Fragment;
            import android.app.ProgressDialog;
            import android.content.Context;
            import android.content.Intent;
            import android.view.LayoutInflater;
            import android.view.View;
            import android.view.ViewGroup;
            import android.widget.AdapterView;
            import android.widget.ListView;

            public class FavoritesFragment extends Fragment {

                Context thisContext;
                private MainActivity myActivity;

                private ViewGroup container;
                private View rootView;

                private ListView mFavoriteList;                 
                private ArrayList<FavoriteItem> favoriteItems;
                private FavoriteListAdapter adapter;
                private FavoritesFragment thisFragment;

                public FavoritesFragment(){}

                @Override
                public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

                    rootView = inflater.inflate(R.layout.fragment_favorites, container, false);
                    this.container = container;

                    //Get a reference to the fragments activity 
                    myActivity = (MainActivity)getActivity();   

                    RestoreAllItems();

                    //Declare the favorite array
                    favoriteItems = new ArrayList<FavoriteItem>();

                    //Load the favorite array
                    callGetFavorites();

                    return rootView;

                }

                private void RestoreAllItems()
                {

                    //Get a reference to the fragments Context
                    thisContext = container.getContext();

                    //Get a reference to the Fragment
                    thisFragment = this;

                    mFavoriteList = (ListView) rootView.findViewById(R.id.list_browse);

                    mFavoriteList.setOnItemClickListener(new FavoriteClickListener());


                }

                /**
                 * Item click listener
                 * */
                private class FavoriteClickListener implements ListView.OnItemClickListener {
                    @Override
                    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

                        FavoriteItem item = favoriteItems.get(position);

                            Intent iIntent = new Intent(thisContext, DetailActivity.class);

                            iIntent.putExtra("animal_id", item.getAnimalID());

                            startActivityForResult(iIntent, ACTIVITY_PET_DETAIL);

                    }
                }  

                //Method called from the ListAdapter when an items checkbox changes
                public void checkChanged(int position, boolean isChecked) {

                    if (position < favoriteItems.size()) {      
                        FavoriteItem item = favoriteItems.get(position);
                        item.setSelected(isChecked);

                        favoriteItems.set(position, item);
                    }


                }

                //Load the favoriteItems array
                private void getFavorites(String url) {
                    final ProgressDialog dialog;    

                    dialog = new ProgressDialog(thisContext);         
                    dialog.setMessage("Loading, please wait...");         
                    dialog.setIndeterminate(true);         
                    dialog.setCancelable(false);         
                    dialog.show();     

                    favoriteItems = new ArrayList<FavoriteItem>();

                    JsonArrayRequest req = new JsonArrayRequest(url, new Response.Listener<JSONArray> () {  

                        @Override
                        public void onResponse(JSONArray response) {
                            try {
                                ....

                                for (int i = 0; i < response.length(); i++) {

                                ....

                                    // Load the favoriteItems array
                                    favoriteItems.add(new FavoriteItem(name, breed, sex, age_long, animal_id));

                                }

                                try {

                                    //When the array is fully loaded set the ListAdapter
                                    adapter = new FavoriteListAdapter(thisContext, favoriteItems, thisFragment);
                                    mFavoriteList.setAdapter(adapter);

                                } catch (Exception e) {
                                   e.printStackTrace();
                                } 

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

                            dialog.dismiss();
                        }


                    }, new Response.ErrorListener() {
                        @Override
                        public void onErrorResponse(VolleyError error) {
                            VolleyLog.e("Error: ", error.getMessage());
                            Log.e("Error: ", error.getMessage());
                            dialog.dismiss();
                        }
                    }) {

                       @Override
                       public Map<String, String> getHeaders() throws AuthFailureError {
                           HashMap<String, String> headers = new HashMap<String, String>();
                                String authValue = "Bearer " + apiToken;
                                headers.put("Authorization", authValue);
                                headers.put("Accept", "application/json; charset=UTF-8");
                                headers.put("Content-Type", "application/json; charset=UTF-8");
                           return headers;
                       };
                    };

                    // add the request object to the queue to be executed
                    MyApplication.getInstance().addToRequestQueue(req);
                }   
            }

Then, the ListAdapter: FavoriteListAdapter.java

            package org.mycompany.TEST.adapter;

            import java.util.ArrayList;

            import org.mycompany.TEST.FavoritesFragment;
            import org.mycompany.TEST.R;
            import org.mycompany.TEST.model.FavoriteItem;

            import android.app.Activity;
            import android.content.Context;
            import android.view.LayoutInflater;
            import android.view.View;
            import android.view.ViewGroup;
            import android.widget.BaseAdapter;
            import android.widget.CheckBox;
            import android.widget.CompoundButton;
            import android.widget.CompoundButton.OnCheckedChangeListener;
            import android.widget.ImageView;
            import android.widget.TextView;


            public class FavoriteListAdapter extends BaseAdapter {

                private Context context;
                private FavoritesFragment thisFragment;
                private ArrayList<FavoriteItem> favoriteItems;
                private boolean isEditing = false;


                public FavoriteListAdapter(Context context, ArrayList<FavoriteItem> favoriteItems, FavoritesFragment thisFragment){
                    //Reference to the Context
                    this.context = context;
                    //Reference to the ArrayList
                    this.favoriteItems = favoriteItems;
                    //Reference to the Fragment that created the ListAdapter
                    this.thisFragment = thisFragment;
                }

                @Override
                public int getCount() {
                    return favoriteItems.size();
                }

                @Override
                public Object getItem(int position) {       
                    return favoriteItems.get(position);
                }

                @Override
                public long getItemId(int position) {
                    return position;
                }

                @Override
                public View getView(int position, View convertView, ViewGroup parent) {

                    if (convertView == null) {
                        //Context allows you to get the LayoutInflater
                        LayoutInflater mInflater = (LayoutInflater)context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
                        convertView = mInflater.inflate(R.layout.favorite_list_item, null);
                    }

                     TextView txtName = (TextView) convertView.findViewById(R.id.name);
                    CheckBox chkSelected = (CheckBox) convertView.findViewById(R.id.isSelected);

                    txtName.setText(favoriteItems.get(position).getName());
                    chkSelected.setChecked(favoriteItems.get(position).isSelected());
                    //Store the position in the list of this list item
                    chkSelected.setTag("" + position);
                    chkSelected.setOnCheckedChangeListener(new OnCheckedChangeListener() 
                    {

                        public void onCheckedChanged(CompoundButton chkBox, boolean isChecked) 
                        {
                            //Get the position out of the tag when the checkbox changes
                            String sPos = (String) chkBox.getTag();
                            int position = Integer.parseInt(sPos);

                            //Call the checkChanged method in the Fragment
                            thisFragment.checkChanged(position, isChecked);
                        }
                    });

                    return convertView;
                }

            }

Answer 2

 val adapter: MyListAdapter
    //Not sure how to instantiate MyListAdapter

Will go:

listView.adapter = MyListAdapter(context, R.layout.row, list)

The context ( this.context , where this is your HomeFragment and context is from getContext() ) will be used in your adapter to inflate you list row (resource = R.layout.row)

In the case that you need your activity as context you can instantiate your list adapter like this:

listView.adapter = MyListAdapter(activity, R.layout.row, list)

where activity is from getActivity()

In either case you'll get access to your application's resources to get the Model.img.