Question

我对这个整个Android开发很新，但我希望创建一个简单的Android应用程序，利用sql数据库，cardViews和RecycleView。我到目前为止的应用程序工作，但我试图添加一个按钮到DetailedActivity，这将允许我从数据库中删除条目。

所需的工作流程将是：

获取数据
选择CardView
点击新按钮（将是删除）
返回CardView，删除按钮所在的条目按下并填充CardView。

RecyclerAdapter.java

package com.example.prabhu.databasedemo;

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

    }

    @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) {
            Intent intent = new Intent(context,DetailsActivity.class);

            Bundle extras = new Bundle();
            extras.putInt("position",getAdapterPosition());
            intent.putExtras(extras);

            /*
            int i=getAdapterPosition();
            intent.putExtra("position", getAdapterPosition());*/
            context.startActivity(intent);
            Toast.makeText(RecyclerAdapter.context, "you have clicked Row " + getAdapterPosition(), Toast.LENGTH_SHORT).show();
        }
    }
}

DatabaseHelper.java

package com.example.prabhu.databasedemo;
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_SHORT);
        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

package com.example.prabhu.databasedemo;


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;
    }
}

MainActivity.java

package com.example.prabhu.databasedemo;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

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

public class MainActivity extends AppCompatActivity {
    EditText etName,etRoll,etAddress,etBranch,etEmail;
    Button btnSubmit,btngetdata;
    DatabaseHelpher helpher;
    List<DatabaseModel> dbList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        dbList= new ArrayList<DatabaseModel>();
        etName = (EditText)findViewById(R.id.etName);
        etRoll = (EditText)findViewById(R.id.etRoll);
        etAddress =(EditText)findViewById(R.id.etAddress);
        etBranch = (EditText)findViewById(R.id.etBranch);
        etEmail = (EditText)findViewById(R.id.etEmail);
        btnSubmit  =(Button)findViewById(R.id.btnSubmit);
        btngetdata =(Button)findViewById(R.id.btngetdata);
        btngetdata.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(MainActivity.this, SecondActivity.class));

               // startActivity(new Intent(MainActivity.this, DetailsActivity.class));

            }
        });

        btnSubmit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                String name=etName.getText().toString();
                String email=etEmail.getText().toString();
                String roll=etRoll.getText().toString();
                String address=etAddress.getText().toString();
                String branch=etBranch.getText().toString();

            if(name.equals("") || email.equals("") || roll.equals("") ||address.equals("")||branch.equals("")){
                Toast.makeText(MainActivity.this,"Please fill all the fields",Toast.LENGTH_SHORT).show();
            }else {
                helpher = new DatabaseHelpher(MainActivity.this);
                helpher.insertIntoDB(name, email, roll, address, branch);
            }
                etName.setText("");
                etRoll.setText("");
                etAddress.setText("");
                etBranch.setText("");
                etEmail.setText("");

                Toast.makeText(MainActivity.this, "insert value", Toast.LENGTH_SHORT);

            }
        });

    }


}

SecondActivity.java

package com.example.prabhu.databasedemo;

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);

    }

    @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);
    }
}

DetailedActivity.java

package com.example.prabhu.databasedemo;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import android.widget.Toast;

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

public class DetailsActivity extends AppCompatActivity {
    DatabaseHelpher helpher;
    List<DatabaseModel> dbList;
    int position;
    TextView tvname,tvemail,tvroll,tvaddress,tvbranch;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_details);

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);


        Intent intent = getIntent();
        Bundle bundle = intent.getExtras();

        // 5. get status value from bundle
         position = bundle.getInt("position");

        tvname =(TextView)findViewById(R.id.name);
        tvemail =(TextView)findViewById(R.id.email);
        tvroll =(TextView)findViewById(R.id.roll);
        tvaddress =(TextView)findViewById(R.id.address);
        tvbranch =(TextView)findViewById(R.id.branch);
        helpher = new DatabaseHelpher(this);
        dbList= new ArrayList<DatabaseModel>();
        dbList = helpher.getDataFromDB();

        if(dbList.size()>0){
            String name= dbList.get(position).getName();
            String email=dbList.get(position).getEmail();
            String roll=dbList.get(position).getRoll();
            String address=dbList.get(position).getAddress();
            String branch=dbList.get(position).getBranch();
            tvname.setText(name);
            tvemail.setText(email);
            tvroll.setText(roll);
            tvaddress.setText(address);
            tvbranch.setText(branch);
        }

        Toast.makeText(DetailsActivity.this, dbList.toString(), Toast.LENGTH_SHORT);
    }


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



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


}

我在DetailedAvtivity.java中添加了一个带有OnClickListener的按钮（findViewByID）。但是，最初只显示吐司，当点击任何详细视图上的按钮时，没有任何反应 - 没有吐司。

所以，问题是：

我在哪里定义按钮以及在哪里实现onClickListener？
如何让按钮删除条目？现在我很高兴使用来自电子邮件TextView（tvemail）的电子邮件，但我将不得不返回并刷新卡片。

提前全部谢谢

Answer 1

过了一段时间我找到了答案。我正在做的是正确的，但搞砸了吐司的命令。

基本上需要做的是

delButton = (Button) findViewById(R.id.button);

delButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Toast.makeText(getApplicationContext(), tvemail.getText() + " deleted", Toast.LENGTH_SHORT).show();
            startActivity(new Intent(DetailsActivity.this, MainActivity.class));
            helpher.deleteARow((String) tvemail.getText());
        }
    });

使用db helper和recycleView完成android cardView

1 个答案: