从SQLite中删除项目后,RecyclerView是否不更新？[副本]

Question

我已经从sqlite中填充了RecolyerView。当单击每一行时，row将从sqlite中删除，但删除后RecolyerView不显示更新的列表。回收器视图仅在再次启动活动后显示更新的列表。我的问题是，在没有刷新的情况下，从recylcerview中删除一个项目后，如何很快更新回收器视图。

下面是我的代码

SecondActivity.java

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;

import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;

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

public class SecondActivity extends AppCompatActivity {
    DatabaseHelpher helpher;
    List<DatabaseModel> dbList;
RecyclerView mRecyclerView;
    private RecyclerView.Adapter mAdapter;
    private RecyclerView.LayoutManager mLayoutManager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);


        helpher = new DatabaseHelpher(this);
        dbList= new ArrayList<DatabaseModel>();
        dbList = helpher.getDataFromDB();


        mRecyclerView = (RecyclerView)findViewById(R.id.recycleview);

        mRecyclerView.setHasFixedSize(true);

        // use a linear layout manager
        mLayoutManager = new LinearLayoutManager(this);
        mRecyclerView.setLayoutManager(mLayoutManager);

        // specify an adapter (see also next example)
        mAdapter = new RecyclerAdapter(this,dbList);
        mRecyclerView.setAdapter(mAdapter);
mAdapter.notifyDataSetChanged ();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_second, menu);
        return true;
    }



    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case android.R.id.home:
                finish();
                return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

DatabaseHelpher.java

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 android.widget.Toast;

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

public class DatabaseHelpher extends SQLiteOpenHelper {
    private static final String DATABASE_NAME="student";
    private static final int DATABASE_VERSION = 1;
    private static final String STUDENT_TABLE = "stureg";
    private static final String STU_TABLE = "create table "+STUDENT_TABLE +"(name TEXT,email TEXT primary key,roll TEXT,address TEXT,branch TEXT)";

Context context;

    public DatabaseHelpher(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        this.context = context;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        db.execSQL(STU_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

        db.execSQL("DROP TABLE IF EXISTS " + STUDENT_TABLE);

        // Create tables again
        onCreate(db);
    }
/* Insert into database*/
    public void insertIntoDB(String name,String email,String roll,String address,String branch){
        Log.d("insert", "before insert");

        // 1. get reference to writable DB
        SQLiteDatabase db = this.getWritableDatabase();

        // 2. create ContentValues to add key "column"/value
        ContentValues values = new ContentValues();
        values.put("name", name);
        values.put("email", email);
        values.put("roll", roll);
         values.put("address", address);
        values.put("branch", branch);

        // 3. insert
        db.insert(STUDENT_TABLE, null, values);
        // 4. close
        db.close();
        Toast.makeText(context, "insert value", Toast.LENGTH_LONG);
        Log.i("insert into DB", "After insert");
    }
/* Retrive  data from database */
    public List<DatabaseModel> getDataFromDB(){
        List<DatabaseModel> modelList = new ArrayList<DatabaseModel>();
        String query = "select * from "+STUDENT_TABLE;

        SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(query,null);

        if (cursor.moveToFirst()){
            do {
                DatabaseModel model = new DatabaseModel();
                model.setName(cursor.getString(0));
                model.setEmail(cursor.getString(1));
                model.setRoll(cursor.getString(2));
                model.setAddress(cursor.getString(3));
                model.setBranch(cursor.getString(4));

                modelList.add(model);
            }while (cursor.moveToNext());
        }


        Log.d("student data", modelList.toString());


        return modelList;
    }


    /*delete a row from database*/

    public void deleteARow(String email){
        SQLiteDatabase db= this.getWritableDatabase();
        db.delete(STUDENT_TABLE, "email" + " = ?", new String[] { email });
        db.close();
    }

}

DatabaseModel.java

public class DatabaseModel {
    private String name;
    private String roll;
    private String address;
    private String branch;
    private String email;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getRoll() {
        return roll;
    }

    public void setRoll(String roll) {
        this.roll = roll;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getBranch() {
        return branch;
    }

    public void setBranch(String branch) {
        this.branch = branch;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

回收适配器.java

import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;

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


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

  static   List<DatabaseModel> dbList;
    static  Context context;

    static DatabaseHelper dh;
    RecyclerAdapter(Context context, List<DatabaseModel> dbList ){
        this.dbList = new ArrayList<DatabaseModel>();
        this.context = context;
        this.dbList = dbList;
dh=new DatabaseHelper(context);
    }

    @Override
    public RecyclerAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        View itemLayoutView = LayoutInflater.from(parent.getContext()).inflate(
                R.layout.item_row, null);

        // create ViewHolder

        ViewHolder viewHolder = new ViewHolder(itemLayoutView);
        return viewHolder;
    }

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

        holder.name.setText(dbList.get(position).getName());
        holder.email.setText(dbList.get(position).getEmail());

    }

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

    public static class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

        public TextView name,email;

        public ViewHolder(View itemLayoutView) {
            super(itemLayoutView);
            name = (TextView) itemLayoutView
                    .findViewById(R.id.rvname);
            email = (TextView)itemLayoutView.findViewById(R.id.rvemail);
            itemLayoutView.setOnClickListener(this);

        }

        @Override
        public void onClick(View v) {
           dh.delete(dbList.get(getAdapterPosition()).getEmail);


            Toast.makeText(RecyclerAdapter.context, "you have clicked Row " + getAdapterPosition(), Toast.LENGTH_LONG).show();
        }
    }
}

我已尝试使用MAdapter.NotifyDataSetChanged（）；更新recyclerview，但它对我不起作用。请给我建议。谢谢

Answer 1

从arraylist和database中删除数据，然后通知list将更新。

或

从数据库中删除数据，删除后从数据库中获取数据并用新数据重新加载arraylist即可完成工作

dbList.remove(getAdapterPosition());
notifyDataSetChanged();
//or use this for better perfomance.
notifyItemRemoved(getAdapterPosition());

移除方法中的传递位置