如何为BMI应用添加SQLite数据库以存储用户体重指数记录？

Got it, let's get your SQLite integration sorted for your BMI app. Here's a step-by-step solution that builds on your existing code to save and view BMI history:

Step 1: Create the Database Helper Class #

First, make a new class called BMIDatabaseHelper to handle database setup and operations. This is Android's standard way to manage SQLite databases.

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import java.util.ArrayList;
import java.util.HashMap;

public class BMIDatabaseHelper extends SQLiteOpenHelper {
    // Core database config
    private static final String DATABASE_NAME = "BMIHistory.db";
    private static final int DATABASE_VERSION = 1;

    // Table and column definitions
    private static final String TABLE_BMI = "bmi_records";
    private static final String COLUMN_ID = "_id";
    private static final String COLUMN_BMI_VALUE = "bmi_value";
    private static final String COLUMN_BMI_CATEGORY = "bmi_category";
    private static final String COLUMN_RECORD_DATE = "record_date";

    public BMIDatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // Create the BMI records table
        String CREATE_TABLE_QUERY = "CREATE TABLE " + TABLE_BMI + "("
                + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
                + COLUMN_BMI_VALUE + " REAL,"
                + COLUMN_BMI_CATEGORY + " TEXT,"
                + COLUMN_RECORD_DATE + " DATETIME DEFAULT CURRENT_TIMESTAMP"
                + ")";
        db.execSQL(CREATE_TABLE_QUERY);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop old table and re-create on version upgrade
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_BMI);
        onCreate(db);
    }

    // Insert a new BMI record into the database
    public void insertBMIRecord(float bmiValue, String category) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(COLUMN_BMI_VALUE, bmiValue);
        values.put(COLUMN_BMI_CATEGORY, category);
        // Insert row (record_date uses default current timestamp)
        db.insert(TABLE_BMI, null, values);
        db.close();
    }

    // Fetch all saved BMI records, sorted by most recent first
    public ArrayList<HashMap<String, String>> getAllBMIRecords() {
        ArrayList<HashMap<String, String>> recordList = new ArrayList<>();
        String fetchQuery = "SELECT * FROM " + TABLE_BMI + " ORDER BY " + COLUMN_RECORD_DATE + " DESC";

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

        // Loop through results and build the list
        if (cursor.moveToFirst()) {
            do {
                HashMap<String, String> record = new HashMap<>();
                record.put("bmi", String.valueOf(cursor.getFloat(cursor.getColumnIndexOrThrow(COLUMN_BMI_VALUE))));
                record.put("category", cursor.getString(cursor.getColumnIndexOrThrow(COLUMN_BMI_CATEGORY)));
                record.put("date", cursor.getString(cursor.getColumnIndexOrThrow(COLUMN_RECORD_DATE)));
                recordList.add(record);
            } while (cursor.moveToNext());
        }
        cursor.close();
        db.close();
        return recordList;
    }
}

Step 2: Update Your MainActivity #

Now modify your MainActivity to use the database helper, implement save/view functionality, and fix a small typo in your input validation.

First, add a member variable for the database helper:

private BMIDatabaseHelper dbHelper;
private String currentBMICategory; // To store the calculated BMI category for saving

Initialize the helper in onCreate:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    height = findViewById(R.id.height);
    weight = findViewById(R.id.weight);
    result = findViewById(R.id.result);
    // Initialize database helper
    dbHelper = new BMIDatabaseHelper(this);
}

Update displayBMI to track the current category (needed for saving):

private void displayBMI(float bmi) {
    currentBMICategory = "";
    if (Float.compare(bmi, 15f) <= 0) {
        currentBMICategory = getString(R.string.v_sev_underweight);
    } else if (Float.compare(bmi, 15f) > 0 && Float.compare(bmi, 16f) <= 0) {
        currentBMICategory = getString(R.string.sev_underweight);
    } else if (Float.compare(bmi, 16f) > 0 && Float.compare(bmi, 18.5f) <= 0) {
        currentBMICategory = getString(R.string.underweight);
    } else if (Float.compare(bmi, 18.5f) > 0 && Float.compare(bmi, 25f) <= 0) {
        currentBMICategory = getString(R.string.healthy);
    } else if (Float.compare(bmi, 25f) > 0 && Float.compare(bmi, 30f) <= 0) {
        currentBMICategory = getString(R.string.overweight);
    } else if (Float.compare(bmi, 30f) > 0 && Float.compare(bmi, 35f) <= 0) {
        currentBMICategory = getString(R.string.obese1);
    } else if (Float.compare(bmi, 35f) > 0 && Float.compare(bmi, 40f) <= 0) {
        currentBMICategory = getString(R.string.obese2);
    } else {
        currentBMICategory = getString(R.string.obese3);
    }
    String bmiLabel = bmi + "\n\n" + currentBMICategory;
    result.setText(bmiLabel);
}

Fix the input validation typo in calculateBMI (you had three quotes instead of two):

public void calculateBMI(View v) {
    String heightStr = height.getText().toString();
    String weightStr = weight.getText().toString();
    // Fixed the quote typo here
    if (heightStr != null && !"".equals(heightStr) && weightStr != null && !"".equals(weightStr)) {
        float heightValue = Float.parseFloat(heightStr) / 100;
        float weightValue = Float.parseFloat(weightStr);
        float bmi = weightValue / (heightValue * heightValue);
        displayBMI(bmi);
    }
}

Implement the saveBMI method (add a View parameter if you're calling this from a button click):

public void saveBMI(View v) {
    if (currentBMICategory == null || currentBMICategory.isEmpty()) {
        Toast.makeText(this, "Calculate your BMI first!", Toast.LENGTH_SHORT).show();
        return;
    }
    // Extract BMI value from the result text
    String resultText = result.getText().toString();
    float bmiValue = Float.parseFloat(resultText.split("\n")[0]);
    // Save to database
    dbHelper.insertBMIRecord(bmiValue, currentBMICategory);
    Toast.makeText(this, "BMI record saved successfully!", Toast.LENGTH_SHORT).show();
}

Implement the viewBMI method to display history in a dialog:

public void viewBMI(View v) {
    ArrayList<HashMap<String, String>> records = dbHelper.getAllBMIRecords();
    if (records.isEmpty()) {
        Toast.makeText(this, "No BMI records found!", Toast.LENGTH_SHORT).show();
        return;
    }
    // Build the history text
    StringBuilder historyBuilder = new StringBuilder();
    for (HashMap<String, String> record : records) {
        historyBuilder.append("Date: ").append(record.get("date")).append("\n")
                .append("BMI: ").append(record.get("bmi")).append("\n")
                .append("Category: ").append(record.get("category")).append("\n\n");
    }
    // Show dialog with history
    new AlertDialog.Builder(this)
            .setTitle("Your BMI History")
            .setMessage(historyBuilder.toString())
            .setPositiveButton("Close", null)
            .show();
}

Step 3: Add Buttons to Your Layout (Optional) #

Update your activity_main.xml to add save and view buttons:

<Button
    android:id="@+id/save_btn"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Save BMI"
    android:onClick="saveBMI"/>

<Button
    android:id="@+id/view_history_btn"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="View History"
    android:onClick="viewBMI"/>

Quick Notes #

• Don't forget to add imports for Toast, AlertDialog, and other used classes to your MainActivity.
• For better UX, you could move history display to a separate activity with a RecyclerView instead of a dialog, but this implementation works for a quick start.

内容的提问来源于stack exchange，提问作者JSTAN