在SQL Lite上第一次尝试。我创建了一个数据库,几乎没有问题可以在示例测验中实现。现在这里是问题。 1.完成所有问题后,它会抛出调试错误,因为close()缺失。 2.如果我实现close(),应用程序崩溃 3.无论close()如何,db创建都不会更新并显示旧数据,需要卸载并重新安装app才能再次运行。
这是我的数据库帮助程序类文件中的代码。
package ccccc
import java.util.ArrayList;
import java.util.List;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DbHelper extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "QuizOnline";
// tasks table name
private static final String TABLE_QUEST = "quest";
// tasks Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_QUES = "question";
private static final String KEY_ANSWER = "answer"; //correct option
private static final String KEY_OPTA= "opta"; //option a
private static final String KEY_OPTB= "optb"; //option b
private static final String KEY_OPTC= "optc"; //option c
private static final String KEY_OPTD= "optd"; //option d
private SQLiteDatabase dbase;
public DbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
dbase=db;
String sql = "CREATE TABLE IF NOT EXISTS " + TABLE_QUEST + " ( "
+ KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + KEY_QUES
+ " TEXT, " + KEY_ANSWER+ " TEXT, "+KEY_OPTA +" TEXT, "
+KEY_OPTB +" TEXT, "+KEY_OPTC +" TEXT, "+KEY_OPTD+" TEXT)";
db.execSQL(sql);
addQuestions();
}
private void addQuestions()
{
Question q1=new Question("Highest mountain peak in the world"+"?","Everest","K2","T3","P3","Everest");
this.addQuestion(q1);
//...........>omited rest questions/entries added
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldV, int newV) {
// Drop older table if existed
db.execSQL("DROP TABLE IF EXISTS " + TABLE_QUEST);
// Create tables again
onCreate(db);
}
// Adding new question
public void addQuestion(Question quest) {
//SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_QUES, quest.getQUESTION());
values.put(KEY_ANSWER, quest.getANSWER());
values.put(KEY_OPTA, quest.getOPTA());
values.put(KEY_OPTB, quest.getOPTB());
values.put(KEY_OPTC, quest.getOPTC());
values.put(KEY_OPTD, quest.getOPTD());
// Inserting Row
dbase.insert(TABLE_QUEST, null, values);
//dbase.close();-----> close given here
}
public List<Question> getAllQuestions() {
List<Question> quesList = new ArrayList<Question>();
// Select All Query
String selectQuery = "SELECT * FROM " + TABLE_QUEST;
dbase=this.getReadableDatabase();
Cursor cursor = dbase.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
Question quest = new Question();
quest.setID(cursor.getInt(0));
quest.setQUESTION(cursor.getString(1));
quest.setANSWER(cursor.getString(2));
quest.setOPTA(cursor.getString(3));
quest.setOPTB(cursor.getString(4));
quest.setOPTC(cursor.getString(5));
quest.setOPTD(cursor.getString(6));
quesList.add(quest);
} while (cursor.moveToNext());
}
// return quest list
return quesList;
}
public int rowcount()
{
int row=0;
String selectQuery = "SELECT * FROM " + TABLE_QUEST;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
row=cursor.getCount();
return row;
}
}
日志:
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: close() was never explicitly called on database '/data/data/com.xxx.quiz/databases/QuizOnline'
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: android.database.sqlite.DatabaseObjectNotClosedException: Application did not close the cursor or database object that was opened here
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.database.sqlite.SQLiteDatabase.<init>(SQLiteDatabase.java:1943)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:1007)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:986)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:1051)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.app.ContextImpl.openOrCreateDatabase(ContextImpl.java:787)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:221)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:157)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:231)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at com.xxx.quiz.DbHelper.getAllQuestions(DbHelper.java:267)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at com.xxx.quiz.QuizActivity.onCreate(QuizActivity.java:43)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.app.Activity.performCreate(Activity.java:4492)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.app.ActivityThread.access$600(ActivityThread.java:123)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.os.Handler.dispatchMessage(Handler.java:99)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.os.Looper.loop(Looper.java:137)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at android.app.ActivityThread.main(ActivityThread.java:4424)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at java.lang.reflect.Method.invokeNative(Native Method)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at java.lang.reflect.Method.invoke(Method.java:511)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
01-09 10:16:16.038 19636-19645/com.xxx.quiz E/SQLiteDatabase: at dalvik.system.NativeStart.main(Native Method)
01-09 10:16:16.048 19636-19645/com.xxx.quiz E/System: Uncaught exception thrown by finalizer
01-09 10:16:16.048 19636-19645/com.xxx.quiz E/System: java.lang.IllegalStateException: Don't have database lock!
01-09 10:16:16.048 19636-19645/com.xxx.quiz E/System: at android.database.sqlite.SQLiteDatabase.verifyLockOwner(SQLiteDatabase.java:2090)
01-09 10:16:16.048 19636-19645/com.xxx.quiz E/System: at android.database.sqlite.SQLiteDatabase$1.entryRemoved(SQLiteDatabase.java:2182)
01-09 10:16:16.048 19636-19645/com.xxx.quiz E/System: at android.database.sqlite.SQLiteDatabase$1.entryRemoved(SQLiteDatabase.java:2178)
01-09 10:16:16.048 19636-19645/com.xxx.quiz E/System: at android.util.LruCache.trimToSize(LruCache.java:197)
01-09 10:16:16.048 19636-19645/com.xxx.quiz E/System: at android.util.LruCache.evictAll(LruCache.java:285)
01-09 10:16:16.048 19636-19645/com.xxx.quiz E/System: at android.database.sqlite.SQLiteDatabase.deallocCachedSqlStatements(SQLiteDatabase.java:2143)
01-09 10:16:16.048 19636-19645/com.xxx.quiz E/System: at android.database.sqlite.SQLiteDatabase.closeClosable(SQLiteDatabase.java:1126)
01-09 10:16:16.048 19636-19645/com.xxx.quiz E/System: at android.database.sqlite.SQLiteDatabase.finalize(SQLiteDatabase.java:1914)
01-09 10:16:16.048 19636-19645/com.xxx.quiz E/System: at java.lang.Daemons$FinalizerDaemon.doFinalize(Daemons.java:182)
01-09 10:16:16.048 19636-19645/com.xxx.quiz E/System: at java.lang.Daemons$FinalizerDaemon.run(Daemons.java:168)
01-09 10:16:16.048 19636-19645/com.xxx.quiz E/System: at java.lang.Thread.run(Thread.java:856)
答案 0 :(得分:1)
您不得保留提供给onCreate()
和onUpdate()
的数据库副本。
对于实际的数据访问:你可以
getWritableDatabase()
一次,并在某处保存引用(正如您对dbase
所做的那样)或每次都会调用getWritableDatabase()
,并在您完成后调用close()
,然后不保持参考。
在这种情况下,为了确保对象始终关闭,您应该使用try
/ finally
:
SQLiteDatabase db = getWritableDatabase();
try {
... use db ...
} finally {
db.close();
}
如果你混合使用这两种方法,你很可能会经常或过少地致电close()
。
游标总是需要close()
d。