Nullpointerexception trying to implement search on listview

Question

I have created a SQL database using an AsyncTask that takes in inputs in one activity and displays them in another activity. Now I am trying to learn how to search the database in listview using a searchview.

I have an adapter class that binds to the listview. In it there is a filter function, to filter the searchview, which is where I believe the error originates from; since the error occurs at adapter.filter(s);.

My Error:

7167-7167/com.example.andrewg.sqltutorial E/AndroidRuntime: FATAL EXCEPTION: 
main
Process: com.example.andrewg.sqltutorial, PID: 7167
java.lang.NullPointerException: Attempt to invoke virtual method 'void 
com.example.andrewg.sqltutorial.ProductAdapter.filter(java.lang.String)' on a 
null object reference
    at
com.example.andrewg.sqltutorial.DisplayProduct$1.onQueryTextChange
(DisplayProduct.java:47)
    at android.widget.SearchView.onTextChanged(SearchView.java:1250)
    at android.widget.SearchView.access$2100(SearchView.java:98)
    at android.widget.SearchView$10.onTextChanged(SearchView.java:1776)
    at android.widget.TextView.sendOnTextChanged(TextView.java:9754)
    at android.widget.TextView.handleTextChanged(TextView.java:9851)
    at android.widget.TextView$ChangeWatcher.onTextChanged(TextView.java:12512)
    at android.text.SpannableStringBuilder.sendTextChanged(SpannableStringBuilder.java:1263)
    at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:575)
    at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:506)
    at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:36)
    at android.view.inputmethod.BaseInputConnection.replaceText(BaseInputConnection.java:843)
    at android.view.inputmethod.BaseInputConnection.setComposingText(BaseInputConnection.java:616)
    at com.android.internal.view.IInputConnectionWrapper.executeMessage(IInputConnectionWrapper.java:396)
    at com.android.internal.view.IInputConnectionWrapper$MyHandler.handleMessage(IInputConnectionWrapper.java:85)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6649)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:826)

DisplayDatabase.java

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ListView;
import android.widget.SearchView;

public class DisplayProduct extends AppCompatActivity {

ListView listView;
ProductAdapter adapter;

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

    listView = findViewById(R.id.Display_listview);

    BackgroundTask backgroundTask = new BackgroundTask(this);
    backgroundTask.execute("get_info");

   //-----------------------------EDIT--------------------------------
   adapter = new ProductAdapter(this, R.layout.display_product_row);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu, menu);

    MenuItem myActionMenuItem = menu.findItem(R.id.action_search);
    SearchView searchView = (SearchView) myActionMenuItem.getActionView();
    searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
        @Override
        public boolean onQueryTextSubmit(String s) {
            return false;
        }

        @Override
        public boolean onQueryTextChange(String s) {

            if(TextUtils.isEmpty(s)){
                adapter.filter("");
                listView.clearTextFilter();
            }
            else{
                adapter.filter(s);
            }

            return true;
        }
    });

    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();

    if(id == R.id.action_settings){
        //do your functionality here
        return true;
    }

    return super.onOptionsItemSelected(item);
}
}

ProductAdapter.java

import android.content.Context;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;
import java.util.Locale;

public class ProductAdapter extends ArrayAdapter {

List list = new ArrayList();

//Menu Search
Context context;
ArrayList<Product> productArrayList = new ArrayList<>();


public ProductAdapter(@NonNull Context context, int resource) {
    super(context, resource);
    this.context = context;
    this.productArrayList.addAll(list);
}

public void addList(ArrayList<Product> Oldarraylist){
    this.productArrayList = Oldarraylist;
}

public void add(Product object) {
    list.add(object);
    super.add(object);
}

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

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

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    //Referencing each row as a View, which is an object
    View row = convertView;
    ProductHolder productHolder;

    if(row == null){
        //There is no view at this position, so we are creating a new one
        //In this case we are inflating an XML layout

        LayoutInflater layoutInflater = (LayoutInflater) this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        row = layoutInflater.inflate(R.layout.display_product_row, parent, false);

        //Locate the views in row.xml
        productHolder = new ProductHolder();
        productHolder.id = row.findViewById(R.id.ID);
        productHolder.name = row.findViewById(R.id.NAME);
        productHolder.price = row.findViewById(R.id.PRICE);
        productHolder.quantity = row.findViewById(R.id.QUANTITY);

        /*setTag is very useful for custom ArrayAdapter using. It is some kind of optimization.
         There setTag used as reference to object that references on some parts of layout
         (that displaying in ListView) instead of findViewById.
         */

        row.setTag(productHolder);
    }

    else{
        //We are recycling a view that already exists
        productHolder = (ProductHolder) row.getTag();
    }

    //Once we have a reference to the View we are returning, we set its values
    //Setting results into textviews

    Product product = (Product) getItem(position);
    productHolder.id.setText(product.getID().toString());
    productHolder.name.setText(product.getName().toString());
    productHolder.price.setText(Integer.toString(product.getPrice()));
    productHolder.quantity.setText(Integer.toString(product.getQuantity()));

    //Menu
    //Listview item clicks

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

        }
    });

    return row;
}

//Menu
public void filter(String charText){
    charText = charText.toLowerCase(Locale.getDefault());
    list.clear();

    if(charText.length() == 0){
        list.addAll(productArrayList);
    }
    else{
        for (Product product : productArrayList){
            if(product.getName().toLowerCase(Locale.getDefault()).contains(charText)){
                list.add(product);
            }
        }
    }
    notifyDataSetChanged();
}

static class ProductHolder{

    TextView id, name, price, quantity;

}
}

Relevant Code in my AsyncTask thread

public class BackgroundTask extends AsyncTask<String,Product,String> {

Context context;
ProductAdapter productAdapter;
Activity activity;
ListView listView;

ArrayList<Product> arrayList = new ArrayList<>();

@Override
protected String doInBackground(String... params) {
    listView = activity.findViewById(R.id.Display_listview);
        SQLiteDatabase db = dbOperations.getReadableDatabase();
        Cursor cursor = dbOperations.getInformation(db);

        productAdapter = new ProductAdapter(context, 
  R.layout.display_product_row);

        String id, name;
        int price, quantity;

        while(cursor.moveToNext()){
            id = 
  cursor.getString(cursor.getColumnIndex(ProductContract.ProductEntry.ID));
            name = 
 cursor.getString(cursor.getColumnIndex(ProductContract.ProductEntry.NAME));
            price = 
 cursor.getInt(cursor.getColumnIndex(ProductContract.ProductEntry.PRICE));
            quantity = 
 cursor.getInt(cursor.getColumnIndex(ProductContract.ProductEntry.QUANTITY));

            Product product = new Product(id, name, price, quantity);

            publishProgress(product);
        }

        return "get_info";
}

@Override
protected void onPostExecute(String s) {
   //Bind the array adapter to the listview
   listView.setAdapter(productAdapter);
   productAdapter.addList(arrayList);

    @Override
protected void onProgressUpdate(Product... values) {
    productAdapter.add(values[0]);
    arrayList.add(values[0]);
}

Welcome to StackOverflow! After looking at your code, it looks like you haven’t initialized `productAdapter` in `DisplayDatabase.java` or your background task. — Greg Whatley, Jun 13 '18 at 00:05
It's complaining because `adapter` is null when you do this: `adapter.filter("");`. Make sure it's not null and you'll be fine. — DataDino, Jun 13 '18 at 00:06
Wrap the line that invokes `adapter` with an `if (adapter != null){`. Then figure out why the variable has null before you run it. — Eric Leschinski, Jun 13 '18 at 00:08

Psypher · Answer 1 · 2018-06-13T00:42:24.660

0

You haven't initialized the ProductAdapter adapter; before you invoked product.filter() method. The adapter is null when you are invoking filter() in onQueryTextChange hence the error.

The code you have right now might have worked if the ProductAdapter class was declared static, since its not you have to create a new instance of the class before invoking methods in the class.

You need to have ProductAdapter adapter= new ProductAdapter() before calling the filter method.

The same is in the BackgroundTask class, you have not intitialized the adapter variable before calling add or addList.

edited Jun 13 '18 at 00:42

answered Jun 13 '18 at 00:36

Psypher

10,717
12
59
83

Thanks that was my issue. The program doesn't crash anymore but the search functionality isn't working. – David Jun 13 '18 at 01:13
If the answer helped can you mark it answered and the next problem in another question – Psypher Jun 13 '18 at 01:29

score 0 · Accepted Answer · answered Jun 13 '18 at 01:18

0

As @Psypher pointed out, you have to have initialized ProductAdapter. However, just adding ProductAdapter adapter = new ProductAdapter() in your AsyncTask won't work, since it's not referring to the same object that you created before.

You'll need to create the adapter first, then pass it into the AsyncTask (or make it static).

answered Jun 13 '18 at 01:18

Tyler V

9,694
3
26
52

I had a feeling that was the issue the search wasn't working. How would I pass the adapter into the asyncTask? – David Jun 13 '18 at 02:05
Add a constructor for BackgroundTask that takes it as an argument (so you would create the adapter, then call "new BackgroundTask(this,adapter)" in onCreate). You can always ask a followup question if needed. No idea why this was downvoted, but hope it helps :) – Tyler V Jun 13 '18 at 02:10
Finally!! IT WORKS! thanks Tyler, I greatly appreciate it. I tried upvoting your response but my reputation is too low – David Jun 13 '18 at 02:13
No worries, it happens. Welcome to SO. – Tyler V Jun 13 '18 at 02:14

Nullpointerexception trying to implement search on listview

2 Answers2