我正在从Firebase中获取一些数据，并尝试将数据保存到同一onDataChange method中的SQLite数据库中。以下是到目前为止我尝试过的代码。我正在将获取的数据保存在String变量中。当我尝试使用Toast时，它显示获取的值，并且当我对String drivername="some value"这样的变量使用硬编码的值时，它会将数据保存到sqlite，但是当我尝试保存获取的数据时值，它返回空值，因此不保存。我在做什么错
String mobile_no=localSharedPreferences.getSharedPreferences(Constants.PhoneNumber);
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Driver");
reference.orderByKey().equalTo(mobile_no).addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
String drivermobile=localSharedPreferences.getSharedPreferences(Constants.PhoneNumber);
for(DataSnapshot datas: dataSnapshot.getChildren()){
String drivername = datas.child("d_nme").getValue(String.class);
String avatorurl = datas.child("d_avtr").getValue(String.class);
String vehicleno = datas.child("v_No").getValue(String.class);
String vehiclename = datas.child("v_nme").getValue(String.class);
//Toast is showing fetched drivername correctly
Toast.makeText(SigninActivity.this, drivername, Toast.LENGTH_SHORT).show();
//Trying to save into SQLITE
ContactsDB db = new ContactsDB(getApplicationContext());
db.open();
db.createEntry(drivermobile, drivername, vehiclename, avatorurl, vehicleno);
db.close();
Toast.makeText(SigninActivity.this, localSharedPreferences.getSharedPreferences(Constants.dDrivername), Toast.LENGTH_SHORT).show();
}
这是我的ContactsDB类
public class ContactsDB {
public static final String KEY_ROWID="_id";
public static final String DRIVER_MOBILE="driver_mobile";
public static final String DRIVER_NAME="driver_firstname";
public static final String VEHICLE_NAME="vehicle_name";
public static final String AVATOR_URL="driver_avator";
public static final String VEHICLE_NO="vehicle_no";
private final String DATABASE_NAME="ContactsDB";
private final String DATABASE_TABLE="ContactsTable";
private final int DATABASE_VERSION=1;
private DBHelper ourHelper;
private final Context ourContext;
private SQLiteDatabase ourDatabse;
public ContactsDB(Context context)
{
ourContext=context;
}
private class DBHelper extends SQLiteOpenHelper
{
public DBHelper(Context context)
{
super(context,DATABASE_NAME,null,DATABASE_VERSION);
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
sqLiteDatabase.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
onCreate(sqLiteDatabase);
}
@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
/**
* THIS Only runs if database not exists with specified version
*/
String sqlcode="CREATE TABLE " + DATABASE_TABLE + " (" +
KEY_ROWID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
DRIVER_MOBILE + " INTEGER NOT NULL, " +
DRIVER_NAME + " TEXT NOT NULL, " +
VEHICLE_NAME + " TEXT NOT NULL, " +
AVATOR_URL + " TEXT NOT NULL, " +
VEHICLE_NO + " DECIMAL NOT NULL);";
sqLiteDatabase.execSQL(sqlcode);
}
}
public ContactsDB open() throws SQLException
{
ourHelper=new DBHelper(ourContext);
ourDatabse=ourHelper.getWritableDatabase();
return this;
}
public void close()
{
ourHelper.close();
}
public long createEntry(String drivermobile, String drivername, String vehiclename, String avatorurl, String vehicleno) {
ContentValues cv = new ContentValues();
cv.put(DRIVER_MOBILE, drivermobile);
cv.put(DRIVER_NAME,drivername);
cv.put(VEHICLE_NAME,vehiclename);
cv.put(AVATOR_URL,avatorurl);
cv.put(VEHICLE_NO,vehicleno);
return ourDatabse.insert(DATABASE_TABLE, null, cv);
}
public String getData()
{
/*Here you can Specify which column value you want to retrieve*/
String [] columns=new String[] {KEY_ROWID,DRIVER_MOBILE,DRIVER_NAME,VEHICLE_NAME,AVATOR_URL,VEHICLE_NO};
Cursor c=ourDatabse.query(DATABASE_TABLE, columns, null,null,null,null,null);
String result="";
int iKeyID=c.getColumnIndex(KEY_ROWID);
int iRowID=c.getColumnIndex(DRIVER_MOBILE);
int iFirstName=c.getColumnIndex(DRIVER_NAME);
int iSecondName=c.getColumnIndex(VEHICLE_NAME);
int iAvatorUrl=c.getColumnIndex(AVATOR_URL);
int iRatings=c.getColumnIndex(VEHICLE_NO);
for(c.moveToFirst();!c.isAfterLast();c.moveToNext())
{
result=result + c.getString(iKeyID) + ": " + c.getString(iRowID) + ": " + c.getString(iFirstName) + ": " +
c.getString(iSecondName) + ": " + c.getString(iAvatorUrl) + "+ " +
c.getString(iRatings) + "\n"; // n is for newline
}
c.close();
return result;
}
public long deleteEntry(String rowId)
{
return ourDatabse.delete(DATABASE_TABLE, KEY_ROWID + "=?", new String[]{rowId});
}
public long updateEntry(String rowId, String drivermobile, String drivername, String vehiclename, String avatorurl, String vehicleno)
{
ContentValues cv=new ContentValues();
/*if you update one column then put only one column or put as many as many you want to update*/
cv.put(DRIVER_MOBILE, drivermobile);
cv.put(DRIVER_NAME,drivername);
cv.put(VEHICLE_NAME,vehiclename);
cv.put(AVATOR_URL,avatorurl);
cv.put(VEHICLE_NO,vehicleno);
return ourDatabse.update(DATABASE_TABLE, cv, KEY_ROWID + "=?", new String[]{rowId});
}
最佳答案
我建议您尝试以下方法：
1。
将以下getter方法添加到ContactsDB.java中：
public SQLiteDatabase getOurDatabse() {
return ourDatabse;
}
2
将打开和关闭分别移动到循环之前和之后，并在循环之前和循环之后还包含一个beginTransaction setTransactionSuccessful和endTransaction。
这样，磁盘将只写入一次，而不是每次插入。
例如：-
public void onDataChange(DataSnapshot dataSnapshot) {
ContactsDB db = new ContactsDB(getApplicationContext());
db.open();
db.getOurDatabse().beginTransaction();
String drivermobile = localSharedPreferences.getSharedPreferences(Constants.PhoneNumber);
for (DataSnapshot datas : dataSnapshot.getChildren()) {
String drivername = datas.child("d_nme").getValue(String.class);
String avatorurl = datas.child("d_avtr").getValue(String.class);
String vehicleno = datas.child("v_No").getValue(String.class);
String vehiclename = datas.child("v_nme").getValue(String.class);
//Toast is showing fetched drivername correctly
Toast.makeText(SigninActivity.this, drivername, Toast.LENGTH_SHORT).show();
//Trying to save into SQLITE
if (drivermobile != null && drivername != null && vehiclename != null && avatorurl != null && vehicleno != null) {
if (db.createEntry(drivermobile, drivername, vehiclename, avatorurl, vehicleno) > 0) {
Toast.makeText(SigninActivity.this, localSharedPreferences.getSharedPreferences(Constants.dDrivername), Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(SigninActivity.this, "?????? Not ADDED", Toast.LENGTH_SHORT).show();
}
} else {
Toast.makeText(SigninActivity.this, "?????? Unable to ADD due to NULL value(s)", Toast.LENGTH_SHORT).show();
}
}
db.getOurDatabse().setTransactionSuccessful();
db.getOurDatabse().endTransaction();
db.close();
此外，这还会进行一些检查，以使null值不会导致尝试插入，但会敬告它无法添加该行。
它还检查每个插入的返回值，以查看是否插入了该行以及相应的Toast。
但是，我建议将消息而不是Toast（或消息）写入Log会有助于调试。
关于firebase - 如何将数据从Firebase保存到SQLite Android，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/59211269/