java - 如何检查在editText中插入的文本是否存在于SQLite数据库中，如果存在则返回一条消息，如果不存在则返回不同的消息

Question

我是编程新手，我正在尝试制作一个应用程序来创建 SQLite 数据库，向所述数据库添加一个表，允许我更新表并查看插入其中的数据。然后，我希望它检查我插入 editText 的文本(例如姓名)是否存在于数据库中并返回一条消息，如果找到文本，则返回一条消息，假设“员工存在”，如果找到则返回一条不同的消息“找不到员工”该名称不在数据库中。

除了应用程序应该检查数据库中是否存在该名称并返回消息的部分之外，我已经成功完成了所有操作。据我所知，这是:

DatabaseHelper 看起来像这样:

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

import androidx.annotation.Nullable;

public class DatabaseHelper extends SQLiteOpenHelper {
    private static final int dbVersion = 1;
    public static final String DATABASE_NAME="numere_masini.db";
    public static final String TABLE_NAME="tabel_masini";
    public static final String COL_1="ID";
    public static final String COL_2="NUME";
    public static final String COL_3="PRENUME";
    public static final String COL_4="NUMAR_DOSAR";
    public static final String COL_5="COD_ORGANIGRAMA";
    public static final String COL_6="CENTRU_COST";
    public static final String COL_7="NUMAR_AUTO_1";
    public static final String COL_8="NUMAR_AUTO_2";
    public static final String COL_9="NUMAR_AUTO_3";
    SQLiteDatabase db;
    private static final String createTable = "Create Table " + TABLE_NAME + "("
            + COL_1 + " Integer Primary Key AutoIncrement," +
            COL_2 + " Text," +
            COL_3 + " Text," +
            COL_4 + " Text," +
            COL_5 + " Text," +
            COL_6 + " Text," +
            COL_7 + " Text," +
            COL_8 + " Text," +
            COL_9 + " Text" + ");";


    public DatabaseHelper(@Nullable Context context) {
        super(context, DATABASE_NAME, null,dbVersion );

    }



    @Override
    public void onCreate(SQLiteDatabase SQLiteDatabase) {
        this.db= SQLiteDatabase;
        db.execSQL(createTable);

    }

    @Override
    public void onUpgrade(SQLiteDatabase SQLiteDatabase, int i, int i1) {
        String query = "DROP TABLE IF EXISTS" + TABLE_NAME;
        db.execSQL(query);
        this.onCreate(db);

    }


    public boolean cautaNumar(){
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.query(TABLE_NAME, new String[]{COL_2}, COL_2+"=?", new String[] {}, null, null, null, "1");
        if (cursor.moveToFirst()) {
            return true; // a row was found
        }
        return false; // no row was found

    }

MainActivity是这个

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

import android.database.Cursor;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    DatabaseHelper myDb;
    EditText editNume, editPrenume, editNumar_dosar,  editCod_organigrama, editCentru_cost, editNumar_auto_1, editNumar_auto2, editNumar_auto3,editTextId, editCauta;
    Button btnAdaugaNumar;
    Button btnverificaNumar;
    Button btnActualizeazaInformatii;
    Button btnAfiseazaDb;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myDb=new DatabaseHelper(this);
        editNume= (EditText)findViewById(R.id.editText_nume);
        editPrenume= (EditText)findViewById(R.id.editText_prenume);
        editNumar_dosar= (EditText)findViewById(R.id.editText_numar_dosar);
        editCod_organigrama= (EditText)findViewById(R.id.editText_cod_organigrama);
        editCentru_cost= (EditText)findViewById(R.id.editText_centru_cost);
        editNumar_auto_1= (EditText)findViewById(R.id.editText_numar_auto_1);
        editNumar_auto2= (EditText)findViewById(R.id.editText_numar_auto_2);
        editNumar_auto3= (EditText)findViewById(R.id.editText_numar_auto_3);
        editTextId=(EditText)findViewById(R.id.editText_id) ;
        editCauta=(EditText) findViewById(R.id.editText_cauta);

        btnAdaugaNumar=(Button)findViewById(R.id.button_adauga_angajat);
        btnverificaNumar= (Button) findViewById(R.id.button_verifica_numar);
        btnActualizeazaInformatii=(Button) findViewById(R.id.button_actualizeaza_informatii);
        btnAfiseazaDb=(Button) findViewById((R.id.button_afiseaza_db));
        AddData();
        viewAll();
        UpdateData();
        verificaNumar();
    }

    // i have no idea how ro write this segment
     public void verificaNumar (){

        String cautare= editCauta.getText().toString();
        if(myDb.cautaNumar()) {

            Toast.makeText(MainActivity.this, "employee exist", Toast.LENGTH_LONG).show();
        }
        else{
            Toast.makeText(MainActivity.this,"employee not found", Toast.LENGTH_LONG).show();
        }

    }

Answer 1

在DatabaseHelper类中:

public boolean cautaNumar(String name){
        boolean flag = false;
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.query(TABLE_NAME, new String[]{COL_2}, COL_2+"=?", new String[] {}, null, null, null, "1");
        if (cursor.moveToFirst()) {
            if(cursor.getString("name").equalsIgnoreCase(name)) {
                flag = true;
            }
            else {
                flag = false;
            }
        }
        return flag;
    }

在类 MainActivity 中:

public void verificaNumar (){
            String cautare = editCauta.getText().toString();
            if(myDb.cautaNumar(cautare)) {
                Toast.makeText(MainActivity.this, "employee exist", Toast.LENGTH_LONG).show();
            }
            else{
                Toast.makeText(MainActivity.this,"employee not found", Toast.LENGTH_LONG).show();
            }
        }