[英]Android Sqlite java.lang.nullpointer exception
I am using SQLite in Android eclipse, however it gives me a java.lang.nullpointerexception in the function createEntry. 我在Android eclipse中使用SQLite,但是它在函数createEntry中给了我java.lang.nullpointerexception。 I tried using Questoid SQLite manager to view the database file and it does show up with the table created. 我尝试使用Questoid SQLite管理器来查看数据库文件,但它确实与创建的表一起显示。 Where's the bug? 错误在哪里?
public class Transact {
public static final String KEY_ROWID = "_id";
public static final String KEY_TAG = "saved_tag";
private static final String DATABASE_NAME = "MyDatabaseName";
private static final String DATABASE_TABLE = "tagsTable";
private static final int DATABASE_VERSION = 1;
private DbHelper ourHelper;
private final Context ourContext;
private SQLiteDatabase ourDatabase;
private static class DbHelper extends SQLiteOpenHelper{
public DbHelper(Context context){
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL(
"CREATE TABLE " + DATABASE_TABLE + " (" + KEY_ROWID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + KEY_TAG + " TEXT NOT NULL);"
);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
onCreate(db);
}
}
public Transact(Context c ){
ourContext = c;
}
public Transact open() throws SQLException{
ourHelper = new DbHelper(ourContext);
ourHelper.getWritableDatabase();
return this;
}
public void close(){
ourHelper.close();
}
public long createEntry(String tagword) {
// TODO Auto-generated method stub
ContentValues cv = new ContentValues();
cv.put(KEY_TAG, tagword);
return ourDatabase.insert(DATABASE_TABLE, "", cv);
}
public String getData() {
// TODO Auto-generated method stub
String[] columns = new String[]{KEY_ROWID, KEY_TAG};
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null, null, null);
String result = "";
int iRow = c.getColumnIndex(KEY_ROWID);
int iTag = c.getColumnIndex(KEY_TAG);
for(c.moveToFirst();!c.isAfterLast();c.moveToNext()){
result = result + c.getString(iRow) + " " + c.getString(iTag) + "\n";
}
return null;
}
}
Code for the add button from Main.java class: Main.java类中添加按钮的代码:
case R.id.addDB:
boolean doneAdd = true;
try{
String tag = textTag.getText().toString();
Transact entry = new Transact(Main.this);
entry.open();
entry.createEntry(tag);
entry.close();
}catch(Exception e){
String error = e.toString();
Dialog d = new Dialog(this);
d.setTitle("Error");
TextView tv = new TextView(this);
tv.setText(error);
d.setContentView(tv);
d.show();
doneAdd = false;
}finally{
if(doneAdd){
Dialog d = new Dialog(this);
d.setTitle("Addition done");
TextView tv = new TextView(this);
tv.setText("Success");
d.setContentView(tv);
d.show();
}
}
break;
You are using ourDatabase
variable without initializing it. 您正在使用ourDatabase
变量,而没有对其进行初始化。 So not only insert you will get nullpointerexception
everywhere where you are using ourDatabase
variable 因此,不仅插入,而且在使用ourDatabase
变量的任何地方都将获得nullpointerexception
you can use something like following in constructor. 您可以在构造函数中使用类似以下的内容。
SQLiteDatabase db = context.openOrCreateDatabase(DATABASE_NAME,
Context.MODE_PRIVATE, null);
used this code in sq light java file
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
public class SQLiteAdapter {
Cursor cursor;
public static final String MYDATABASE_NAME = "MY_DATABASE";
public static final String MYDATABASE_TABLE = "MY_TABLE";
public static final int MYDATABASE_VERSION = 2;
public static final String KEY_ID = "_id";
public static final String KEY_CONTENT1 = "Content1";
public static final String KEY_CONTENT2 = "Content2";
public static final String KEY_CONTENT3 = "Content3";
public static final String KEY_CONTENT4 = "Content4";
public static final String KEY_CONTENT5 = "Content5";
public static final String KEY_CONTENT6 = "Content6";
public static final String KEY_CONTENT7 = "Content7";
public static final String KEY_CONTENT8 = "Content8";
public static final String KEY_CONTENT9 = "Content9";
public static final String KEY_CONTENT10 = "Content10";
public static final String KEY_CONTENT11 = "Content11";
public static final String KEY_CONTENT12 = "Content12";
// create table MY_DATABASE (ID integer primary key, Content text not null);
private static final String SCRIPT_CREATE_DATABASE = "create table "
+ MYDATABASE_TABLE + " (" + KEY_ID
+ " integer primary key autoincrement, " + KEY_CONTENT1
+ " text not null, " + KEY_CONTENT2 + " text not null, "
+ KEY_CONTENT3 + " text not null, " + KEY_CONTENT4
+ " text not null, " + KEY_CONTENT5 + " text not null, "
+ KEY_CONTENT6 + " text not null, " + KEY_CONTENT7
+ " text not null, " + KEY_CONTENT8 + " text not null, "
+ KEY_CONTENT9 + " text not null, " + KEY_CONTENT10
+ " text not null, " + KEY_CONTENT11 + " blob not null, "
+ KEY_CONTENT12 + " long not null);";
private SQLiteHelper sqLiteHelper;
private SQLiteDatabase sqLiteDatabase;
private Context context;
public SQLiteAdapter(Context c) {
context = c;
}
public SQLiteAdapter openToRead() throws android.database.SQLException {
sqLiteHelper = new SQLiteHelper(context, MYDATABASE_NAME, null,
MYDATABASE_VERSION);
sqLiteDatabase = sqLiteHelper.getReadableDatabase();
return this;
}
public SQLiteAdapter openToWrite() throws android.database.SQLException {
sqLiteHelper = new SQLiteHelper(context, MYDATABASE_NAME, null,
MYDATABASE_VERSION);
sqLiteDatabase = sqLiteHelper.getWritableDatabase();
return this;
}
public void close() {
sqLiteHelper.close();
}
public class SQLiteHelper extends SQLiteOpenHelper {
public SQLiteHelper(Context context, String name,
CursorFactory factory, int version) {
super(context, name, factory, version);
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL("PRAGMA foreign_keys=ON");
db.execSQL(SCRIPT_CREATE_DATABASE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
}
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