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社区首页 >问答首页 >Nullpointerexception尝试在列表视图上实现搜索

Nullpointerexception尝试在列表视图上实现搜索
EN

Stack Overflow用户
提问于 2018-06-13 08:00:28
回答 2查看 103关注 0票数 1

我已经使用AsyncTask创建了一个SQL数据库,它接受一个活动中的输入,并在另一个活动中显示它们。现在我正在尝试学习如何使用searchview在listview中搜索数据库。

我有一个绑定到listview的适配器类。其中有一个过滤函数,用于过滤搜索视图,我认为这就是错误的来源;因为错误发生在adapter.filter(s);。

我的错误:

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;

}
}

我的AsyncTask线程中的相关代码

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]);
}
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接:

https://stackoverflow.com/questions/50827409

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