我想帮忙,我最近做了一个数据库相关的应用程序:你可以通过代码非常清楚地理解:
要学习SQLite中的数据库,请参阅DatabaseHelper.java--
这是机票预订系统的一个例子
BookingsActivity.java::
package com.example.myapplication;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;
public class BookingsActivity extends AppCompatActivity {
private DatabaseHelper databaseHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_bookings);
databaseHelper = new DatabaseHelper(this);
SQLiteDatabase db = databaseHelper.getReadableDatabase();
Cursor cursor = db.query(DatabaseHelper.TABLE_BOOKINGS, null, null, null, null, null, null);
StringBuilder pastBookings = new StringBuilder();
while (cursor.moveToNext()) {
pastBookings.append("Date: ").append(cursor.getString(cursor.getColumnIndex(DatabaseHelper.COLUMN_DATE)))
.append(", From: ").append(cursor.getString(cursor.getColumnIndex(DatabaseHelper.COLUMN_FROM)))
.append(", To: ").append(cursor.getString(cursor.getColumnIndex(DatabaseHelper.COLUMN_TO)))
.append(", Airline: ").append(cursor.getString(cursor.getColumnIndex(DatabaseHelper.COLUMN_AIRLINE)))
.append("\n");
}
cursor.close();
db.close();
TextView pastBookingsTextView = findViewById(R.id.pastBookingsTextView);
pastBookingsTextView.setText(pastBookings.toString());
}
}
MainActivity.java::
package com.example.myapplication;
import android.content.ContentValues;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
public class MainActivity extends AppCompatActivity {
String[] airlines ={ "Air India", "Indigo", "Air Asia", "SpiceJet"};
String[] places = { "Kolkata", "Mangalore", "Mumbai", "Chennai", "Delhi"};
String[] passengerCounts = {"1", "2", "3", "4", "5"};
String[] ticketClasses = {"Economy", "Business", "First Class"};
private DatabaseHelper databaseHelper;
String date;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
databaseHelper = new DatabaseHelper(this);
Spinner fromSpinner = findViewById(R.id.fromSpinner);
Spinner toSpinner = findViewById(R.id.toSpinner);
Spinner airlineSpinner = findViewById(R.id.airlineSpinner);
Spinner passengerSpinner = findViewById(R.id.passengerSpinner);
Spinner classSpinner = findViewById(R.id.classSpinner);
ArrayAdapter<String> placeAdapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_item, places);
ArrayAdapter<String> airlineAdapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_item, airlines);
ArrayAdapter<String> passengerAdapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_item, passengerCounts);
ArrayAdapter<String> classAdapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_item, ticketClasses);
fromSpinner.setAdapter(placeAdapter);
toSpinner.setAdapter(placeAdapter);
airlineSpinner.setAdapter(airlineAdapter);
passengerSpinner.setAdapter(passengerAdapter);
classSpinner.setAdapter(classAdapter);
Button bookFlightButton = findViewById(R.id.bookFlightButton);
bookFlightButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
bookFlight();
}
});
}
private void bookFlight() {
String date = this.date;
String from = ((Spinner) findViewById(R.id.fromSpinner)).getSelectedItem().toString();
String to = ((Spinner) findViewById(R.id.toSpinner)).getSelectedItem().toString();
String airline = ((Spinner) findViewById(R.id.airlineSpinner)).getSelectedItem().toString();
String passengers = ((Spinner) findViewById(R.id.passengerSpinner)).getSelectedItem().toString();
String ticketClass = ((Spinner) findViewById(R.id.classSpinner)).getSelectedItem().toString();
SQLiteDatabase db = databaseHelper.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(DatabaseHelper.COLUMN_DATE, date);
values.put(DatabaseHelper.COLUMN_FROM, from);
values.put(DatabaseHelper.COLUMN_TO, to);
values.put(DatabaseHelper.COLUMN_AIRLINE, airline);
values.put(DatabaseHelper.COLUMN_PASSENGERS, passengers);
values.put(DatabaseHelper.COLUMN_CLASS, ticketClass);
db.insert(DatabaseHelper.TABLE_BOOKINGS, null, values);
db.close();
Toast.makeText(this,"Booking successful!!",Toast.LENGTH_SHORT).show();
}
}
DatabaseHelper.java:::
package com.example.myapplication;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseHelper extends SQLiteOpenHelper {
static final String DATABASE_NAME = "airline_reservation.db";
static final int DATABASE_VERSION = 1;
static final String TABLE_BOOKINGS = "bookings";
static final String COLUMN_ID = "id";
static final String COLUMN_DATE = "date";
static final String COLUMN_FROM = "from_location";
static final String COLUMN_TO = "to_location";
static final String COLUMN_AIRLINE = "airline";
static final String COLUMN_PASSENGERS = "passengers";
static final String COLUMN_CLASS = "class";
// SQL statement to create the bookings table
private static final String CREATE_TABLE_BOOKINGS = "CREATE TABLE " + TABLE_BOOKINGS +
"(" +
COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
COLUMN_DATE + " TEXT," +
COLUMN_FROM + " TEXT," +
COLUMN_TO + " TEXT," +
COLUMN_AIRLINE + " TEXT," +
COLUMN_PASSENGERS + " TEXT," +
COLUMN_CLASS + " TEXT" +
")";
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_TABLE_BOOKINGS);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// Drop older table if existed
db.execSQL("DROP TABLE IF EXISTS " + TABLE_BOOKINGS);
// Create tables again
onCreate(db);
}
}
activity_bookings.xml::
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".BookingsActivity">
<TextView
android:id="@+id/pastBookingsTextView"
android:layout_width="378dp"
android:layout_height="606dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
activity_main.xml::
<?xml版本=“1.0”编码=“utf-8”>
<androidx.constraintlayout.widget。ConstraintLayout xmlns:android=“http://schemas.android.com/apk/res/android"
xmlns:app=“http://schemas.android.com/apk/res-auto"
xmlns:tools=“http://schemas.android.com/tools"
android:layout_width=“match_parent”
android:layout_height=“match_parent”
工具:context=“.BookingsActivity”>
<文本框
android:id=“@+id/pastBookingsTextView”
android:layout_width=“378dp”
android:layout_height=“606dp”
app:layout_constractBottom_toBottomOf=“父级”
app:layout_contraintEnd_toEndOf=“父级”
app:layout_contraintStart_toStartOf=“父级”
app:layout_contraintTop_toTopOf=“父级”/>
</androidx.constraintlayout.widget。约束布局>
另外,不要忘记在AndroidManifest.xml中使用Intent的活动标记
它应该是这样的:
<activity
android:name=".BookingsActivity"
android:exported="false" />
如果您需要详细信息,请随时询问,这是一个非常简单的程序,可以帮助您学习DatabaseHelper的基础知识。
必须在这里进行代码转储,因为安卓工作室因应用程序崩溃而臭名昭著,即使是一个小错误,等级问题也会非常严重。
