NullPointerException：尝试调用虚拟方法'；android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase
我得到的错误是NullPointerException：尝试调用虚拟方法'；android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase,android,sqlite,nullpointerexception,Android,Sqlite,Nullpointerexception,我得到的错误是 java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory 有关守则- public vo
java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory
public void delete(int position) {
SQLiteDatabase db = getWritableDatabase(); //this is null
db.execSQL("DELETE FROM LOGIN WHERE _ID=1;");
db.close();
}
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;
import static android.content.ContentValues.TAG;
public class DBHelper extends SQLiteOpenHelper {
private Context context;
private DBHelper dbHelper;
public DBHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
this.context = context;
}
@Override public void onCreate(SQLiteDatabase db) {
try {
String DROP_SQL = "drop table if exists LOGIN";
db.execSQL(DROP_SQL);
} catch(Exception ex) {
Log.e(TAG, "Exception in DROP_SQL", ex);
}
StringBuffer sb = new StringBuffer();
sb.append(" CREATE TABLE LOGIN ( ");
sb.append(" _ID INTEGER PRIMARY KEY AUTOINCREMENT, ");
sb.append(" ID TEXT, ");
sb.append(" PW TEXT ) ");
try {
db.execSQL(sb.toString());
} catch(Exception ex) {
Log.e(TAG, "Exception in CREATE_SQL", ex);
}
Toast.makeText(context, R.string.make, Toast.LENGTH_SHORT).show();
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Toast.makeText(context, R.string.upgrade, Toast.LENGTH_SHORT).show();
}
public void addLogin(Login login) {
SQLiteDatabase db = getWritableDatabase();
StringBuffer sb = new StringBuffer();
sb.append(" INSERT INTO LOGIN ( ");
sb.append(" ID, PW ) ");
sb.append(" VALUES ( ?, ? ) ");
if(login.getId().equals("") || login.getPw().equals("")){
Toast.makeText(context, R.string.nodata, Toast.LENGTH_SHORT).show();
}else{
db.execSQL(sb.toString(),
new Object[]{
login.getId(),
login.getPw(),
});;
Toast.makeText(context, R.string.insert, Toast.LENGTH_SHORT).show();
}
}
public void delete(int position) {
SQLiteDatabase db = getWritableDatabase(); //this is null
db.execSQL("DELETE FROM LOGIN WHERE _ID=1;");
db.close();
//????
//db.execSQL("DELETE FROM LOGIN WHERE _ID=" + position + ";");
//?? ???
}
public List getAllData() {
StringBuffer sb = new StringBuffer();
sb.append(" SELECT _ID, ID, PW FROM LOGIN ");
SQLiteDatabase db = getReadableDatabase();
Cursor cursor = db.rawQuery(sb.toString(), null);
List list = new ArrayList();
Login login = null;
while (cursor.moveToNext()) {
login = new Login();
login.set_id(cursor.getInt(0));
login.setId(cursor.getString(1));
login.setPw(cursor.getString(2));
list.add(login);
}
return list;
}
}
请访问com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1120）检查您的应用程序权限。清单和运行时 在哪里设置数据库名称和版本 您可以像这样创建构造函数。您的数据库名称和版本总是相同的
// Database version
private static final int DATABASE_VERSION = 1;
// Database name
private static final String DATABASE_NAME = MyDatabase.db;
public DBHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
this.context = context;
}
显示完整的stacktrace，请读取stacktrace我将检查stacktrace的其余部分是否有错误。数据库可能没有被创建，因为onCreate异常事实上，副本是准确的，上下文是空的