我试图从不同的数据库版本切换。但是，当我最近访问较高的数据库版本时，当我尝试访问较低的数据库版本时，应用程序仍然崩溃。
这是代码
public class DbHelper extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 46;
// Database Name
private static final String DATABASE_NAME = "triviaQuiz";
// 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 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)";
db.execSQL(sql);
addQuestions();
//db.close();
}
private void addQuestions()
{
Question q1=new Question("What does ICT stands for?","Individual Computing Techniques", "Information Computer Technology", "Information Computer Tutorial", "Information Computer Technology");
this.addQuestion(q1);
Question q2=new Question("Information Technology is also classified as the Science and Art of?", "Recording and Storage", "Past Time", "Information", "Recording and Storage");
this.addQuestion(q2);
Question q3=new Question("Based on the lesson, what are the things that you might experience when interacting with other people in the internet?","Free load", "Time Leisure","Cyber Bullying", "Cyber Bullying" );
this.addQuestion(q3);
Question q4=new Question("What are the things you need to consider before turning off the computer?", "Make sure to save all your work", "Make sure to log out your account", "Leave a file open","Make sure to log out your account");
this.addQuestion(q4);
Question q5=new Question("Password must be?","Easy to guess","Easy to remember","Unique and hard to guess by other people","Unique and hard to guess by other people");
this.addQuestion(q5);
}
@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());
// Inserting Row
dbase.insert(TABLE_QUEST, null, values);
}
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));
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;
}
现在，我有5个这样的java文件，每个都有不同的数据库版本。当我切换数据库时，应用程序不断崩溃。无论如何要解决这个问题吗？
这是logcat
03-31 22:45:20.793 25098-25098/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.doepiccoding.navigationdrawer, PID: 25098
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.doepiccoding.navigationdrawer/com.android.pet.view.QuizActivity1}: android.database.sqlite.SQLiteException: Can't downgrade database from version 46 to 45
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5021)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:827)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:643)
at dalvik.system.NativeStart.main(Native Method)
Caused by: android.database.sqlite.SQLiteException: Can't downgrade database from version 46 to 45
at android.database.sqlite.SQLiteOpenHelper.onDowngrade(SQLiteOpenHelper.java:361)
at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:255)
at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:188)
at com.android.pet.view.DbHelper1.getAllQuestions(DbHelper1.java:80)
at com.android.pet.view.QuizActivity1.onCreate(QuizActivity1.java:35)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1090)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5021)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
答案 0 :(得分：1)
要在Android中降级SQLite数据库版本，您需要覆盖{ [Error: scripts/main.js: Unexpected token: name (sidr)]
message: 'scripts/main.js: Unexpected token: name (sidr)',
fileName: 'scripts/main.js',
...
showStack: false,
showProperties: true,
plugin: 'gulp-uglify' }
类的onDowngrade(...)方法。就像你有SQLiteOpenHelper方法一样：
onUpgrade(...)在它下面添加降级方法
@Override
public void onUpgrade(SQLiteDatabase db, int oldV, int newV) {
...
}
但你错误地使用了数据库。不要为每个测验及其问题创建新的DB文件。你只需要一个DB就可以了。甚至不为您的测验创建多个表。所有测验都属于一个表，所有问题都属于另一个表。谷歌一些数据库基础......