java - 当我们尝试在 recylerview 中设置适配器时从 recylerview 收到错误
问题描述
ComponentInfo{enkay.ntucsingapoor/enkay.ntucsingapoor.Activity.BabyDiapers}：尝试在 null 上调用虚拟方法 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)'在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 在 android.app.ActivityThread.-wrap11(Unknown Source:0) 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817) 的对象引用。 app.ActivityThread$H.handleMessage(ActivityThread.java:1593) 在 android.os.Handler.dispatchMessage(Handler.java:105) 在 android.os.Looper.loop(Looper.java:164) 在 android.app.ActivityThread.main(ActivityThread.java:6541) 在 java. lang.reflect.Method.invoke(Native Method) 在 com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767）原因：java.lang.NullPointerException：尝试在 enkay 的空对象引用上调用虚拟方法 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' .ntucsingapoor.Activity.BabyDiapers.SetData(BabyDiapers.java:56) 在 enkay.ntucsingapoor.Activity.BabyDiapers.onCreate(BabyDiapers.java:42) 在 android.app.Activity.performCreate(Activity.java:6975) 在 android。应用程序。仪器。callActivityOnCreate(Instrumentation.java:1213) 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770) 在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 在 android.app.ActivityThread.-wrap11(未知来源:0) 在 android.os.Handler.dispatchMessage(Handler.java:105) 在 android.os.Looper 的 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)。在 com.android.internal.os.Zygote$MethodAndArgsCaller 的 java.lang.reflect.Method.invoke(Native Method) 的 android.app.ActivityThread.main(ActivityThread.java:6541) 的循环（Looper.java:164）。在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) 运行（Zygote.java:240）在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) 的 com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 调用（本机方法）在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) 的 com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 调用（本机方法）
尝试将数据从 Sqite 设置为 Reclyerview 时出现此错误
这是我想要获取数据的活动
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import com.google.android.gms.analytics.ecommerce.Product;
import java.util.ArrayList;
import java.util.List;
import enkay.ntucsingapoor.Adapters.MarketAdapters;
import enkay.ntucsingapoor.Helper.SQlHelper;
import enkay.ntucsingapoor.R;
import enkay.ntucsingapoor.model.MarketModel;
public class BabyDiapers extends AppCompatActivity {
RecyclerView market_data_recylerview;
private static final String TAG = "BabyDiapers";
SQlHelper myDatabaseHelper;
private SQlHelper market;
List<MarketModel> model;
MarketAdapters adapters;
MarketModel marketModel;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_baby_diapers);
SetData();
}
private void SetData() {
model = new ArrayList<>();
market_data_recylerview = (RecyclerView) findViewById(R.id.List_items);
model = new ArrayList<MarketModel>();
myDatabaseHelper = new SQlHelper(BabyDiapers.this);
model = myDatabaseHelper.getAllMarketData();
adapters = new MarketAdapters(model);
final LinearLayoutManager reLayoutManager = new LinearLayoutManager(getApplicationContext());
reLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
market_data_recylerview.setLayoutManager(reLayoutManager);
Log.i(TAG, "onCreate: RecylerView =" + market_data_recylerview);
market_data_recylerview.setItemAnimator(new DefaultItemAnimator());
market_data_recylerview.setHasFixedSize(true);
market_data_recylerview.setAdapter(adapters);
Log.i("HIteshdata", "" + adapters);
}
}
此活动的 Xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_baby_diapers"
android:layout_width="match_parent"
android:background="@color/colorNavIcon"
android:layout_height="match_parent"
tools:context="enkay.ntucsingapoor.Activity.BabyDiapers">
<TextView
android:layout_width="match_parent"
android:layout_height="45dp"
android:text="Search Bar"
android:textSize="34dp"
android:textStyle="bold"/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="53dp"
android:layout_marginTop="48dp"
android:orientation="horizontal"
>
<Button
android:layout_width="99dp"
android:layout_marginLeft="279dp"
android:layout_height="wrap_content"
android:text="GO"
android:background="@color/Yellow"
/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="fill_parent"
android:layout_marginTop="111dp">
<android.support.v7.widget.RecyclerView
android:id="@+id/List_items"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
</android.support.v7.widget.RecyclerView>
</LinearLayout>
</RelativeLayout>
数据库助手类
package enkay.ntucsingapoor.Helper;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import java.util.ArrayList;
import java.util.List;
import enkay.ntucsingapoor.Activity.DataInsert;
import enkay.ntucsingapoor.model.MarketModel;
/**
* Created by lenovo on 8/8/2018.
*/
public class SQlHelper extends SQLiteOpenHelper {
private static final String TAG="SQLHelper";
MarketModel model=new MarketModel();
SQLiteOpenHelper dbhandler;
SQLiteDatabase database;
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "supermarketdata";
private static final String TABLE_NAME = "market_comparision";
private static final String KEY_ID = "id";
private static final String KEY_BRAND_NAME ="brand_name";
private static final String KEY__FAIRPRICE_PRODUCT_NAME = "product_fairprice";
private static final String KEY_FAIRPRICE_PRICE_NO = "price_fairprice";
private static final String KEY__All_IN_FOR_YOU_PRODUCT_NAME = "product_all_in_for_you";
private static final String KEY_ALL_IN_FOR_PRODUCT_PRICE_NO = "price_all_in_for_you";
private static final String KEY__GIANT_ONLINE_PRODUCT_NAME = "product_giant_online";
private static final String KEY_GIANT_ONLINE_PRODUCT_PRICE_NO = "price_giant_online";
private static final String KEY_GIANT_ONLINE_PRODUCT_CATEGERY="categery_giant_online";
private static final String KEY__COLD_STORAGE_PRODUCT_NAME = "product_cold_storage";
private static final String KEY_COLD_STORAGE_PRODUCT_PRICE_NO = "price_cold_storage";
SQLiteDatabase db;
public SQlHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_NAME + "("
+ KEY_ID + " INTEGER PRIMARY KEY,"
+ KEY_BRAND_NAME + " TEXT,"
+ KEY__FAIRPRICE_PRODUCT_NAME + " TEXT,"
+ KEY_FAIRPRICE_PRICE_NO + " TEXT,"
+ KEY__All_IN_FOR_YOU_PRODUCT_NAME + " TEXT,"
+ KEY_ALL_IN_FOR_PRODUCT_PRICE_NO + " TEXT,"
+ KEY__GIANT_ONLINE_PRODUCT_NAME + " TEXT,"
+ KEY_GIANT_ONLINE_PRODUCT_PRICE_NO + " TEXT,"
+ KEY_GIANT_ONLINE_PRODUCT_CATEGERY + " TEXT,"
+ KEY__COLD_STORAGE_PRODUCT_NAME + " TEXT,"
+ KEY_COLD_STORAGE_PRODUCT_PRICE_NO + " TEXT" + ")";
db.execSQL(CREATE_CONTACTS_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int i, int i1) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
public void InsertMArket(MarketModel marketModel) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_BRAND_NAME, marketModel.getBrand_name());
values.put(KEY__FAIRPRICE_PRODUCT_NAME, marketModel.getFair_Price_product());
values.put(KEY_FAIRPRICE_PRICE_NO, marketModel.getFair_Price_Product_Price());
values.put(KEY__All_IN_FOR_YOU_PRODUCT_NAME, marketModel.getAll_In_For_You_Product());
values.put(KEY_ALL_IN_FOR_PRODUCT_PRICE_NO, marketModel.getAll_In_For_You_Product_Price());
values.put(KEY__GIANT_ONLINE_PRODUCT_NAME, marketModel.getGiant_Online_Product());
values.put(KEY_GIANT_ONLINE_PRODUCT_PRICE_NO, marketModel.getGiant_Online_product_price());
values.put(KEY_GIANT_ONLINE_PRODUCT_CATEGERY, marketModel.getGiant_Online_product_categery());
values.put(KEY__COLD_STORAGE_PRODUCT_NAME, marketModel.getCold_Storage_Product());
values.put(KEY_COLD_STORAGE_PRODUCT_PRICE_NO, marketModel.getCold_Storage_price());
db.insert(TABLE_NAME, null, values);
db.close();
}
//public MarketModel getMArket(int id) {
// SQLiteDatabase db = this.getReadableDatabase();
//
// Cursor cursor = db.query(TABLE_NAME, new String[] { KEY_ID,
// KEY_BRAND_NAME,
// KEY__All_IN_FOR_YOU_PRODUCT_NAME,
// KEY_ALL_IN_FOR_PRODUCT_PRICE_NO,
// KEY__FAIRPRICE_PRODUCT_NAME,
// KEY_FAIRPRICE_PRICE_NO,
// KEY__GIANT_ONLINE_PRODUCT_NAME,
// KEY_GIANT_ONLINE_PRODUCT_PRICE_NO,
// KEY_GIANT_ONLINE_PRODUCT_CATEGERY,
// KEY__COLD_STORAGE_PRODUCT_NAME,
// KEY_COLD_STORAGE_PRODUCT_PRICE_NO
// }
// , KEY_ID + "=?",
// new String[] { String.valueOf(id) }, null, null, null, null);
// if (cursor != null)
// cursor.moveToFirst();
//
// MarketModel market = new MarketModel(Integer.parseInt(cursor.getString(0)),
// cursor.getString(1), cursor.getString(2));
//
// return market;
// }
public List<MarketModel> getAllMarketData() {
//Log.i(TAG, "getAllMarketData: checkData = " + MarketModel.class);
String colums[]={
KEY__FAIRPRICE_PRODUCT_NAME,
KEY_FAIRPRICE_PRICE_NO,
KEY_BRAND_NAME,
KEY__All_IN_FOR_YOU_PRODUCT_NAME,
KEY_ALL_IN_FOR_PRODUCT_PRICE_NO,
KEY__GIANT_ONLINE_PRODUCT_NAME,
KEY_GIANT_ONLINE_PRODUCT_PRICE_NO,
KEY_GIANT_ONLINE_PRODUCT_CATEGERY,
KEY__COLD_STORAGE_PRODUCT_NAME,
KEY_COLD_STORAGE_PRODUCT_PRICE_NO
};
String sortOrder =
KEY__FAIRPRICE_PRODUCT_NAME + " ASC";
List<MarketModel> marketList = new ArrayList<MarketModel>();
Log.i(TAG, "getAllMarketData: Data= " + marketList.isEmpty());
//Select Fair_price_product from tablename
//String whereClouse =KEY__FAIRPRICE_PRODUCT_NAME +"=?";
String selectQuery = "SELECT * FROM " + TABLE_NAME;
// String [] selectionArgs=new String[]{"Product"};
Log.i(TAG, "getAllMarketData: DataQuery=" + selectQuery);
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
Log.i(TAG, "getAllMarketData: dataCursor= " + cursor.getCount());
if (cursor.moveToFirst()) {
do {
MarketModel market=new MarketModel();
market.setBrand_name(cursor.getString(cursor.getColumnIndex(KEY_BRAND_NAME)));
market.setFair_Price_product(cursor.getString(cursor.getColumnIndex(KEY__FAIRPRICE_PRODUCT_NAME)));
Log.i(TAG, "getAllMarketData: coding=" + market.getFair_Price_product());
market.setFair_Price_Product_Price(cursor.getString(cursor.getColumnIndex(KEY_FAIRPRICE_PRICE_NO)));
Log.i(TAG, "getAllMarketData: coding=" + market.getFair_Price_Product_Price());
// market.setAll_In_For_You_Product(cursor.getString(cursor.getColumnIndex(KEY__All_IN_FOR_YOU_PRODUCT_NAME)));
// Log.i(TAG, "getAllMarketData: coding=" + market.getFair_Price_product());
// market.setAll_In_For_You_Product_Price(cursor.getString(cursor.getColumnIndex(KEY_ALL_IN_FOR_PRODUCT_PRICE_NO)));
// market.setGiant_Online_Product(cursor.getString(cursor.getColumnIndex(KEY__GIANT_ONLINE_PRODUCT_NAME)));
// market.setGiant_Online_product_price(cursor.getString(cursor.getColumnIndex(KEY_GIANT_ONLINE_PRODUCT_PRICE_NO)));
// market.setGiant_Online_product_categery(cursor.getString(cursor.getColumnIndex(KEY_GIANT_ONLINE_PRODUCT_CATEGERY)));
// market.setCold_Storage_Product(cursor.getString(cursor.getColumnIndex(KEY__COLD_STORAGE_PRODUCT_NAME)));
// market.setCold_Storage_price(cursor.getString(cursor.getColumnIndex(KEY_COLD_STORAGE_PRODUCT_PRICE_NO)));
marketList.add(market);
} while (cursor.moveToNext());
cursor.close();
db.close();
Log.i(TAG, "getAllUser: List empty = "+marketList.isEmpty());
}
return marketList;
}
// public List<MarketModel> getAllMarket()
// {
// String TABLE_NAME="market_comparision";
// MarketModel market=new MarketModel();
// String query = "SELECT * FROM "+TABLE_NAME
// +" WHERE "+KEY__FAIRPRICE_PRODUCT_NAME+" = ?";
//
// Log.i(TAG, "getUserDetail: market = "+market);
//
// Cursor cursor = getReadableDatabase().rawQuery(query, null);
// Log.i(TAG, "getAllMarket: Data " + cursor.getCount());
// while (cursor.moveToNext())
// {
// market.setBrand_name(cursor.getString(cursor.getColumnIndex(KEY_BRAND_NAME)));
// market.setFair_Price_product(cursor.getString(cursor.getColumnIndex(KEY__FAIRPRICE_PRODUCT_NAME)));
// market.setFair_Price_Product_Price(cursor.getString(cursor.getColumnIndex(KEY_FAIRPRICE_PRICE_NO)));
// market.setAll_In_For_You_Product(cursor.getString(cursor.getColumnIndex(KEY__All_IN_FOR_YOU_PRODUCT_NAME)));
// market.setAll_In_For_You_Product_Price(cursor.getString(cursor.getColumnIndex(KEY_ALL_IN_FOR_PRODUCT_PRICE_NO)));
// market.setGiant_Online_Product(cursor.getString(cursor.getColumnIndex(KEY__GIANT_ONLINE_PRODUCT_NAME)));
// market.setGiant_Online_product_price(cursor.getString(cursor.getColumnIndex(KEY_GIANT_ONLINE_PRODUCT_PRICE_NO)));
// market.setGiant_Online_product_categery(cursor.getString(cursor.getColumnIndex(KEY_GIANT_ONLINE_PRODUCT_CATEGERY)));
// market.setCold_Storage_Product(cursor.getString(cursor.getColumnIndex(KEY__COLD_STORAGE_PRODUCT_NAME)));
// market.setCold_Storage_price(cursor.getString(cursor.getColumnIndex(KEY_COLD_STORAGE_PRODUCT_PRICE_NO)));
//
// Log.i(TAG, "getAllMarket: market" +cursor);
// // marketList.add(market);
// }
//
// return (List<MarketModel>) market;
// }
public int updateMArket(MarketModel market) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_BRAND_NAME,DataInsert.marketModel1.getBrand_name());
values.put(KEY__FAIRPRICE_PRODUCT_NAME, DataInsert.marketModel1.getFair_Price_product());
values.put(KEY_FAIRPRICE_PRICE_NO,DataInsert.marketModel1.getFair_Price_Product_Price());
values.put(KEY__All_IN_FOR_YOU_PRODUCT_NAME,DataInsert.marketModel1.getAll_In_For_You_Product());
values.put(KEY_ALL_IN_FOR_PRODUCT_PRICE_NO,DataInsert.marketModel1.getAll_In_For_You_Product_Price());
values.put(KEY__GIANT_ONLINE_PRODUCT_NAME,DataInsert.marketModel1.getGiant_Online_Product());
values.put(KEY_GIANT_ONLINE_PRODUCT_PRICE_NO,DataInsert.marketModel1.getGiant_Online_product_price());
values.put(KEY_GIANT_ONLINE_PRODUCT_CATEGERY,DataInsert.marketModel1.getGiant_Online_product_categery());
values.put(KEY__COLD_STORAGE_PRODUCT_NAME,DataInsert.marketModel1.getCold_Storage_Product());
values.put(KEY_COLD_STORAGE_PRODUCT_PRICE_NO,DataInsert.marketModel1.getCold_Storage_price());
// updating row
return db.update(TABLE_NAME, values, KEY_ID + " = ?",
new String[] { String.valueOf(market.getId()) });
}
// Deleting single contact
public void deleteMarket(MarketModel market) {
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_NAME, KEY_ID + " = ?",
new String[] { String.valueOf(market.getId()) });
db.close();
}
// Getting contacts Count
public int getContactsCount() {
String countQuery = "SELECT * FROM " + TABLE_NAME;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(countQuery, null);
cursor.close();
// return count
return cursor.getCount();
}
}
我的适配器类
package enkay.ntucsingapoor.Adapters;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import java.util.List;
import enkay.ntucsingapoor.R;
import enkay.ntucsingapoor.model.MarketModel;
/**
* Created by lenovo on 9/1/2018.
*/
public class MarketAdapters extends RecyclerView.Adapter<MarketAdapters.MarketViewHolder> {
List<MarketModel> modelList;
public MarketAdapters(List<MarketModel> modelList)
{
this.modelList=modelList;
}
@Override
public MarketViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.activity_baby_diapers,null);
return new MarketViewHolder(view);
}
@Override
public void onBindViewHolder(MarketViewHolder holder, int position) {
MarketModel model=modelList.get(position);
}
@Override
public int getItemCount() {
return modelList.size();
}
public class MarketViewHolder extends RecyclerView.ViewHolder {
public MarketViewHolder(View itemView) {
super(itemView);
}
}
}
解决方案
推荐阅读
- java - 用户登录桌面应用程序时如何隐藏登录/注册表单？
- java - 如果变量的值在过去 24 小时内没有改变
- junit5 - JUnit 从数据库中检索值以测试标准
- dart - 缺少 Dart 空值检查速记？
- python - 在续行中混合普通字符串和 f 字符串
- python - 从另一个数据帧中分配一个数字 - Series([], Name: id, dtype: float64)
- c# - 通过按钮启用和禁用文本框？（asp.net）
- c# - Selenium - 检查元素不存在的等待时间太长
- java - 为什么 getAllTrackables 方法只返回一张脸？
- python - 如何在python中从网络摄像头视频20秒后开始捕获视频帧