[在新计算机上运行项目或删除数据库文件夹时，未在Android Studio中创建SQLite数据库 _数据库文件

五陵年少金市东，银鞍白马渡春风。这篇文章主要讲述[在新计算机上运行项目或删除数据库文件夹时，未在Android Studio中创建SQLite数据库相关的知识，希望能为你提供帮助。
[我已经构建了一个应用程序，其中使用融合位置提供程序可以获取位置，并基于该位置显示来自SQLiteDatabase的特定位置的报告卡。
数据库最初运行良好，但是当我在另一台机器上运行相同的android项目时，它并没有在创建数据库。 Android在设备文件资源管理器-> 数据-> 数据-> 包名称-> 数据库中创建数据库文件夹后。我是通过右键单击“数据库”文件夹并单击“上载”来手动加载以下数据库文件的。数据库文件链接：https://drive.google.com/file/d/197MHiLl8nvFZ5eHStrBR9WfeYvQTtDKm/view?usp=sharing为了尝试了解问题所在，我也从自己的计算机上的项目中删除了数据库文件夹，现在也没有在计算机上创建数据库文件夹。
【[在新计算机上运行项目或删除数据库文件夹时，未在Android Studio中创建SQLite数据库】在将其标记为重复项之前，我已经尝试过以下问题的方法，但仍然无法使用。Android SQLite database table not being createdsqlite database not createdhttps://alvinalexander.com/android/sqliteopenhelper-does-not-call-oncreate-failing-database
请在下面找到我的代码：DatabaseHelper.java

package edu.cpsc6150.co2ut; import android.content.ContentValues; import android.content.Context; import android.database.Cursor; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; public class DatabaseHelper extends SQLiteOpenHelper {public static String DATABASE_NAME = "states"; public static final int DATABASE_VERSION = 1; public static final String TABLE_NAME = "States_Report"; public static final String KEY_ID = "id"; public static final String STATE_NAME = "name"; public static final String STATE_GRADE = "grade"; public static final String EXTREME_HEAT = "heat"; public static final String DROUGHT = "Drought"; public static final String WILDFIRES = "wildfires"; public static final String INLAND_FLOODING = "inlandflooding"; public static final String COASTAL_FLOODING = "coastalflooding"; public static final String CREATE_TABLE_STUDENTS = "CREATE TABLE " + TABLE_NAME + "(" + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + STATE_NAME + " TEXT," + STATE_GRADE + " TEXT," + EXTREME_HEAT + " TEXT," + DROUGHT + " TEXT," + WILDFIRES + " TEXT," + INLAND_FLOODING + " TEXT," + COASTAL_FLOODING + " TEXT)"; public DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); //Log.d("table", CREATE_TABLE_STUDENTS); }//end DatabaseHelper constructor/** * Functionality: Creates tables * PreConditions: needs table names and column names * PostConditions: Table is created */ @Override public void onCreate(SQLiteDatabase db) { db.execSQL(CREATE_TABLE_STUDENTS); }//end onCreate method/** * Functionality: Drop existing table and create new table if table already exists * PreConditions: Database name, oldversion number and newVersion number are required to create a new table * PostConditions: Old table should be dropped and new table should be created */ @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { db.execSQL("DROP TABLE IF EXISTS '" + TABLE_NAME + "'"); onCreate(db); }//end onUpgrade method /* public long addStudentDetail(String state, String grade, String heat, String drought, String wildfires, String iflooding, String cflooding) { SQLiteDatabase db = this.getWritableDatabase(); // Creating content values ContentValues values = new ContentValues(); values.put(STATE_NAME, state); values.put(STATE_GRADE, grade); values.put(EXTREME_HEAT, heat); values.put(DROUGHT, drought); values.put(WILDFIRES, wildfires); values.put(INLAND_FLOODING, iflooding); values.put(COASTAL_FLOODING, cflooding); // insert row in students table long insert = db.insert(TABLE_NAME, null, values); return insert; }*//** * Functionality: Get data from database and Update UI * PreConditions: requires existing populated database * PostConditions: Update reportcard in the UI from the database */ public String[] getData(String state) { /*SQLiteDatabase db = this.getReadableDatabase(); Cursor res =db.rawQuery( "select * from States_Report where name = '"+state+"'", null ); return res; */ String State = state; String[] name = new String[7]; String password; //SQLiteDatabase db = getWritableDatabase(); SQLiteDatabase db = this.getReadableDatabase(); String[] columns = {DatabaseHelper.STATE_NAME,DatabaseHelper.STATE_GRADE,DatabaseHelper.EXTREME_HEAT,DatabaseHelper.DROUGHT,DatabaseHelper.WILDFIRES,DatabaseHelper.INLAND_FLOODING,DatabaseHelper.COASTAL_FLOODING}; Cursor cursor =db.query(DatabaseHelper.TABLE_NAME,columns,"name = '"+state+"' ",null,null,null,null); StringBuffer buffer= new StringBuffer(); while (cursor.moveToNext()) { name[0] =cursor.getString(cursor.getColumnIndex(DatabaseHelper.STATE_NAME)); name[1] =cursor.getString(cursor.getColumnIndex(DatabaseHelper.STATE_GRADE)); name[2] =cursor.getString(cursor.getColumnIndex(DatabaseHelper.EXTREME_HEAT)); name[3] =cursor.getString(cursor.getColumnIndex(DatabaseHelper.DROUGHT)); name[4] =cursor.getString(cursor.getColumnIndex(DatabaseHelper.WILDFIRES)); name[5] =cursor.getString(cursor.getColumnIndex(DatabaseHelper.INLAND_FLOODING)); name[6] =cursor.getString(cursor.getColumnIndex(DatabaseHelper.COASTAL_FLOODING)); }return name; }//end getData method }//end DatabaseHelper class

ReportCardActivity.java（与该特定功能的MainActivity.java类似）

package edu.cpsc6150.co2ut; import android.Manifest; import android.annotation.SuppressLint; import android.app.Activity; import android.content.Intent; import android.content.IntentSender; import android.content.pm.PackageManager; import android.database.sqlite.SQLiteDatabase; import android.location.Address; import android.location.Geocoder; import android.location.Location; import android.net.Uri; import android.os.Bundle; import android.os.Looper; import android.provider.Settings; import android.util.Log; import android.widget.Button; import android.widget.TextView; import android.widget.Toast; import androidx.annotation.NonNull; import androidx.appcompat.app.AppCompatActivity; import androidx.core.app.ActivityCompat; import com.google.android.gms.common.api.ApiException; import com.google.android.gms.common.api.ResolvableApiException; import com.google.android.gms.location.FusedLocationProviderClient; import com.google.android.gms.location.LocationCallback; import com.google.android.gms.location.LocationRequest; import com.google.android.gms.location.LocationResult; import com.google.android.gms.location.LocationServices; import com.google.android.gms.location.LocationSettingsRequest; import com.google.android.gms.location.LocationSettingsResponse; import com.google.android.gms.location.LocationSettingsStatusCodes; import com.google.android.gms.location.SettingsClient; import com.google.android.gms.tasks.OnCompleteListener; import com.google.android.gms.tasks.OnFailureListener; import com.google.android.gms.tasks.OnSuccessListener; import com.google.android.gms.tasks.Task; import com.karumi.dexter.Dexter; import com.karumi.dexter.PermissionToken; import com.karumi.dexter.listener.PermissionDeniedResponse; import com.karumi.dexter.listener.PermissionGrantedResponse; import com.karumi.dexter.listener.PermissionRequest; import com.karumi.dexter.listener.single.PermissionListener; import java.io.IOException; import java.util.List; import java.util.Locale; import butterknife.BindView; import butterknife.ButterKnife; import butterknife.OnClick; public class ReportCardActivity extends AppCompatActivity { private static final String TAG = ReportCardActivity.class.getSimpleName(); @BindView(R.id.location_result) TextView txtLocationResult; @BindView(R.id.btn_start_location_updates) Button btnStartUpdates; private static final long UPDATE_INTERVAL_IN_MILLISECONDS = 10000; private static final long FASTEST_UPDATE_INTERVAL_IN_MILLISECONDS = 5000; private static final int REQUEST_CHECK_SETTINGS = 100; private FusedLocationProviderClient mFusedLocationClient; private SettingsClient mSettingsClient; private LocationRequest mLocationRequest; private LocationSettingsRequest mLocationSettingsRequest; private LocationCallback mLocationCallback; private Location mCurrentLocation; private Boolean mRequestingLocationUpdates; private DatabaseHelper databaseHelper; private TextView statedisplay, gradedisplay, heat, drought, wildfires, inlandFlooding,coastalFlooding; /** * Functionality: Instantiates the DatabaseHelper class and other UI Components like textviews * PreConditions: DatabaseHelper and textviews must be declared * PostConditions: Textviews are assigned and DatabaseHelper initialized */ @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_report_card); ButterKnife.bind(this); databaseHelper = new DatabaseHelper(this); SQLiteDatabase db = new DatabaseHelper(this).getReadableDatabase(); statedisplay = (TextView) findViewById(R.id.statedisplay); gradedisplay = (TextView) findViewById(R.id.gradedisplay); heat = (TextView) findViewById(R.id.heat); drought = (TextView) findViewById(R.id.drought); wildfires = (TextView) findViewById(R.id.wildfires); inlandFlooding = (TextView) findViewById(R.id.inlandFlooding); coastalFlooding = (TextView) findViewById(R.id.coastalFlooding); // initialize the necessary libraries init(); // restore the values from saved instance state restoreValuesFromBundle(savedInstanceState); }//end onCreate method/** * Functionality: Initializes the necessary libraries to get location updates * PreConditions: Library's required for the location updates must be declared * PostConditions: All necessary Libraries are intialized */ private void init() { mFusedLocationClient = LocationServices.getFusedLocationProviderClient(this); mSettingsClient = LocationServices.getSettingsClient(this); mLocationCallback = new LocationCallback() { /** * Functionality: Updates Last location on receiving location updates * PreConditions: Needs to receive locationResult as a parameter * PostConditions: Return updated last location to the UI */@Override public void onLocationResult(LocationResult locationResult) { super.onLocationResult(locationResult); // location is received mCurrentLocation = locationResult.getLastLocation(); updateLocationUI(); } }; mRequestingLocationUpdates = false; mLocationRequest = new LocationRequest(); mLocationRequest.setInterval(UPDATE_INTERVAL_IN_MILLISECONDS); mLocationRequest.setFastestInterval(FASTEST_UPDATE_INTERVAL_IN_MILLISECONDS); mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY); LocationSettingsRequest.Builder builder = new LocationSettingsRequest.Builder(); builder.addLocationRequest(mLocationRequest); mLocationSettingsRequest = builder.build(); }//end init method/** * Functionality: Restores the savedState of the activity * PreConditions: Needs the instance state to be saved * PostConditions: Retrieve the saved state and update the UI */ private void restoreValuesFromBundle(Bundle savedInstanceState) { if (savedInstanceState != null) { if (savedInstanceState.containsKey("is_requesting_updates")) { mRequestingLocationUpdates = savedInstanceState.getBoolean("is_requesting_updates"); }if (savedInstanceState.containsKey("last_known_location")) { mCurrentLocation = savedInstanceState.getParcelable("last_known_location"); } } updateLocationUI(); }//end restoreValuesFromBundle method/** * Functionality: Update the UI displaying the location data * PreConditions: Requires the current location * PostConditions: Updates the UI with the current location and the states report card from the database */ String state; private void updateLocationUI() { if (mCurrentLocation != null) { Geocoder gcd = new Geocoder(this, Locale.getDefault()); try{ List< Address> addresses = gcd.getFromLocation(mCurrentLocation.getLatitude(), mCurrentLocation.getLongitude(), 1); if (addresses.size() > 0) { state = addresses.get(0).getAdminArea(); String output[] = databaseHelper.getData(state); statedisplay.setText("State: "+output[0]); gradedisplay.setText("Average: "+output[1]); heat.setText("Extreme Heat: "+output[2]); drought.setText("Drought: "+output[3]); wildfires.setText("Wildfires: "+output[4]); inlandFlooding.setText("Inland Flooding: "+output[5]); coastalFlooding.setText("Coastal Flooding: "+output[6]); /*Cursor rs = databaseHelper.getData(state); if (rs.moveToFirst()){ // do the workString username = rs.getString(1); String password = rs.getString(2); //String nam = rs.getString(rs.getColumnIndex(DatabaseHelper.STATE_NAME)); //String phon = rs.getString(rs.getColumnIndex(DatabaseHelper.STATE_GRADE)); statedisplay.setText(username); gradedisplay.setText(password); }*///arrayList = databaseHelper.getAllStudentsList(); //tvnames.setText(""); /*for (int i = 0; i < arrayList.size(); i++){ tvnames.setText(tvnames.getText().toString()+", "+arrayList.get(i)); }*/} else { // do your stuff } } catch (IOException e1) { e1.printStackTrace(); }//end try-catch block txtLocationResult.setText( getString(R.string.welcome_message,state) ); // location last updated time } }//end updateLocationUI method/** * Functionality: Saves the Activities current state * PreConditions: Needs the values of mCurrentLocation and mRequestingLocationUpdates * PostConditions: The Instance state should be saved to the Bundle */ @Override public void onSaveInstanceState(Bundle outState) { super.onSaveInstanceState(outState); outState.putBoolean("is_requesting_updates", mRequestingLocationUpdates); outState.putParcelable("last_known_location", mCurrentLocation); }//end onSaveInstanceState method/** * Functionality: Starting location updates * PreConditions: Check whether location settings are satisfied * PostConditions: Location updates will be requested */ private void startLocationUpdates() { mSettingsClient .checkLocationSettings(mLocationSettingsRequest) .addOnSuccessListener(this, new OnSuccessListener< LocationSettingsResponse> () { @SuppressLint("MissingPermission") @Override public void onSuccess(LocationSettingsResponse locationSettingsResponse) { Log.i(TAG, "All location settings are satisfied."); Toast.makeText(getApplicationContext(), "Started location updates!", Toast.LENGTH_SHORT).show(); //noinspection MissingPermission mFusedLocationClient.requestLocationUpdates(mLocationRequest, mLocationCallback, Looper.myLooper()); updateLocationUI(); }//end onSuccess method }) .addOnFailureListener(this, new OnFailureListener() { @Override public void onFailure(@NonNull Exception e) { int statusCode = ((ApiException) e).getStatusCode(); switch (statusCode) { case LocationSettingsStatusCodes.RESOLUTION_REQUIRED: Log.i(TAG, "Location settings are not satisfied. Attempting to upgrade " + "location settings "); try { // Show the dialog by calling startResolutionForResult(), and check the // result in onActivityResult(). ResolvableApiException rae = (ResolvableApiException) e; rae.startResolutionForResult(ReportCardActivity.this, REQUEST_CHECK_SETTINGS); } catch (IntentSender.SendIntentException sie) { Log.i(TAG, "PendingIntent unable to execute request."); }//end try-catch block break; case LocationSettingsStatusCodes.SETTINGS_CHANGE_UNAVAILABLE: String errorMessage = "Location settings are inadequate, and cannot be " + "fixed here. Fix in Settings."; Log.e(TAG, errorMessage); Toast.makeText(ReportCardActivity.this, errorMessage, Toast.LENGTH_LONG).show(); }//end switch statement updateLocationUI(); }//end onFailure method }); }//end startLocationUpdates method/** * Functionality: OnClick will start receiving location updates * PreConditions: Permissions must be granted * PostConditions: Location Updates started */ @OnClick(R.id.btn_start_location_updates) public void startLocationButtonClick() { // Requesting ACCESS_FINE_LOCATION using Dexter library Dexter.withActivity(this) .withPermission(Manifest.permission.ACCESS_FINE_LOCATION) .withListener(new PermissionListener() {@Override public void onPermissionGranted(PermissionGrantedResponse response) { mRequestingLocationUpdates = true; startLocationUpdates(); }//end onPermissionGranted method@Override public void onPermissionDenied(PermissionDeniedResponse response) { if (response.isPermanentlyDenied()) { // open device settings when the permission is // denied permanently openSettings(); } }//end onPermuissionDenied method@Override public void onPermissionRationaleShouldBeShown(PermissionRequest permission, PermissionToken token) { token.continuePermissionRequest(); }//end onPermissionRationaleShouldBeShown method }).check(); }//end startLocationButtonClick method/** * Functionality: Stop or pause location updates when the app pauses * PreConditions: FusedLocationClient must be intialized * PostConditions: Stop Location updates */ public void stopLocationUpdates() { // Removing location updates mFusedLocationClient .removeLocationUpdates(mLocationCallback) .addOnCompleteListener(this, new OnCompleteListener< Void> () { /** * Functionality: * PreConditions: * PostConditions: */ @Override public void onComplete(@NonNull Task< Void> task) { Toast.makeText(getApplicationContext(), "Location updates stopped!", Toast.LENGTH_SHORT).show(); } }); }//end stopLocationUpdates method/** * Functionality: Check whether user has granted permissions or not * PreConditions: Needs requestCode, resultCode and data as parameters * PostConditions: Log the ActivityResult as an error log */ @Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { super.onActivityResult(requestCode, resultCode, data); switch (requestCode) { // Check for the integer request code originally supplied to startResolutionForResult(). case REQUEST_CHECK_SETTINGS: switch (resultCode) { case Activity.RESULT_OK: Log.e(TAG, "User agreed to make required location settings changes."); // Nothing to do. startLocationupdates() gets called in onResume again. break; case Activity.RESULT_CANCELED: Log.e(TAG, "User chose not to make required location settings changes."); mRequestingLocationUpdates = false; break; }//end switch statement break; }//end switch statement }//end onActivityResult method/** * Functionality: Open settings if permissions is denied * PreConditions: Settings URI * PostConditions: Open Application details settings page */ private void openSettings() { Intent intent = new Intent(); intent.setAction( Settings.ACTION_APPLICATION_DETAILS_SETTINGS); Uri uri = Uri.fromParts("package", BuildConfig.APPLICATION_ID, null); intent.setData(uri); intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK); startActivity(intent); }//end openSettings method/** * Functionality: Check for permissions again onResume * PreConditions: App must be paused or stopped before this function is called * PostConditions: onResume the locationupdates must be resume and the UI must be updated */ @Override public void onResume() { super.onResume(); // Resuming location updates depending on button state and // allowed permissions if (mRequestingLocationUpdates & & checkPermissions()) { startLocationUpdates(); } updateLocationUI(); }//end onResume()/** * Functionality: Checks if permission to access location is granted * PreConditions: Permission must be mentioned in the manifest file * PostConditions: Return permission granted if Uses-Permission is mentioned in the activity file */ private boolean checkPermissions() { int permissionState = ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION); return permissionState == PackageManager.PERMISSION_GRANTED; }//end checkPermissions method/** * Functionality: Stops location updates when the application is paused * PreConditions: Application must be paused * PostConditions: Location updates must be stopped */ @Override protected void onPause() { super.onPause(); if (mRequestingLocationUpdates) { // pausing location updates stopLocationUpdates(); } }//end onPause method }//end ReportCardActivity class

让我知道您是否需要有关代码或依赖项的更多信息。
答案我相信正在创建数据库BUT，您似乎没有在填充它。
使用您的Databasehelper（仅将addStudentDetail注释为唯一更改），然后使用：-

public class MainActivity extends AppCompatActivity { DatabaseHelper mDBHelper; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); mDBHelper = new DatabaseHelper(this); mDBHelper.addStudentDetail("STATE1","GRADE1","HIGH","YES","NO","NO","NO"); mDBHelper.addStudentDetail("STATE1","GRADE2","HIGH","YES","NO","NO","NO"); mDBHelper.addStudentDetail("STATE1","GRADE3","HIGH","YES","NO","NO","NO"); mDBHelper.addStudentDetail("STATE1","GRADE4","HIGH","YES","NO","NO","NO"); for (String s: mDBHelper.getData("STATE1")){ Log.d("INFO",s); } } }

结果：-

12-05 16:38:19.211 3764-3764/? D/INFO: STATE1 12-05 16:38:19.211 3764-3764/? D/INFO: GRADE4 12-05 16:38:19.211 3764-3764/? D/INFO: HIGH 12-05 16:38:19.211 3764-3764/? D/INFO: YES 12-05 16:38:19.211 3764-3764/? D/INFO: NO 12-05 16:38:19.211 3764-3764/? D/INFO: NO 12-05 16:38:19.211 3764-3764/? D/INFO: NO

我看不到您在代码中向数据库添加数据的任何地方。相反，您只是尝试使用

String output[] = databaseHelper.getData(state);

来获取数据，因为没有数据，它不会检索任何内容。
另一答案下面我附加了一个解决方案，您只需要在ReportCardActivity.java代码中添加两行代码即可。要添加的两行代码被注释为“ // add this line”，并在其前后有一行astrix（*）。

private Boolean mRequestingLocationUpdates; DatabaseHelper databaseHelper; ********************************************************* SQLiteDatabase database; //add this line ********************************************************* private TextView statedisplay, gradedisplay, heat, drought, wildfires, inlandFlooding,coastalFlooding; /** * Functionality: Instantiates the DatabaseHelper class and other UI Components like textviews * PreConditions: DatabaseHelper and textviews must be declared * PostConditions: Textviews are assigned and DatabaseHelper initialized */ @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_report_card); ButterKnife.bind(this); databaseHelper = new DatabaseHelper(this); ********************************************************* database = databaseHelper.getWritableDatabase(); //add this line ********************************************************* statedisplay = (TextView) findViewById(R.id.statedisplay); gradedisplay = (TextView) findViewById(R.id.gradedisplay); heat = (TextView) findViewById(R.id.heat); drought = (TextView) findViewById(R.id.drought); wildfires = (TextView) findViewById(R.id.wildfires); inlandFlooding = (TextView) findViewById(R.id.inlandFlooding); coastalFlooding = (TextView) findViewById(R.id.coastalFlooding); // initialize the necessary libraries init(); // restore the values from saved instance state restoreValuesFromBundle(savedInstanceState); }//end onCreate method

您粘贴代码的人运行该应用程序。这应该在设备文件资源管理器-> 数据-> 数据-> 包名称目录中创建数据库目录。
该数据库文件夹可能不会立即显示。运行一次应用程序后，您可能必须重新启动android studio。
当您重新启动android studio并转到设备文件资源管理器-> 数据-> 数据-> 包名称目录时，应创建数据库目录。
创建后，右键单击数据库文件夹，然后单击上载，然后上载您在链接中提供的数据库文件。