Question

编辑2，问题解决了 - 问题是我有两个不同的帮助器，一个用于单个数据库中的每个表。这意味着当第一个帮助器被实例化时，它的onCreate方法被调用，并且数据库与一个表一起创建。

当第二个帮助器被实例化时，没有调用onCreate方法，因为数据库已经存在。这意味着未创建第二个表，因此在尝试访问第二个表时会引发错误。

编辑，我想我已经意识到我的问题 - SQLiteHelper引用的是数据库而不是表。我不应该有多个帮助器，只管理所有表。有两个帮助器导致第二个onCreate方法不被调用，因为数据库已经存在。

我有一个数据库的助手类。活动按如下方式创建它的实例 -

storageHelper = new ClassTimeStorageHelper(getApplicationContext());

接下来，调用一个方法来加载数据持有者类的ArrayList -

classes = storageHelper.getAllClasses();

被调用的方法如下 -

public ArrayList<ClassTime> getAllClasses() {
    ArrayList<ClassTime> classes = new ArrayList<>();

    String query = "SELECT * FROM " + TABLE_CLASS_TIMES;
    SQLiteDatabase db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery(query, null);

    ClassTime c;
    if (cursor.moveToFirst()) {
        do {
            c = new ClassTime();
            c.setId(Integer.parseInt(cursor.getString(0)));
            c.setSubjectID(cursor.getInt(1));
            c.setStart(cursor.getInt(2));
            c.setEnd(cursor.getInt(3));
            c.setDay(cursor.getInt(4));
            classes.add(c);
        } while (cursor.moveToNext());
    }
    Log.d("getAllClasses", classes.toString());
    return classes;
}

存储助手的onCreate方法是 -

    @Override
public void onCreate(SQLiteDatabase db) {
    Log.d("OnCreate", "Method called");
    try {
        String CREATE_TABLE_CLASS_TIMES = "CREATE TABLE IF NOT EXISTS " +
                TABLE_CLASS_TIMES +
                "(" + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                KEY_LESSON_ID + " INTEGER, " +
                "FOREIGN KEY(" + KEY_LESSON_ID + ") " + "REFERENCES " + TABLE_SUBJECTS + "(id), " +
                KEY_START_TIME + " INTEGER, " +
                KEY_END_TIME + " INTEGER, " +
                KEY_DAY + " INTEGER )";
        db.execSQL(CREATE_TABLE_CLASS_TIMES);
    } catch (Exception e) {
        Log.d("Exception ", ""+e.getStackTrace());
    }
}

由于缺少日志语句，我可以看到onCreate方法没有被调用，即使我清除了应用程序数据，或者卸载并重新安装。编辑 - 我还尝试创建一个全局SQLiteDatabase变量，并在构造函数中调用db = this.getWriteableDatabase（），然后替换对此方法的其他调用。同样的问题仍然存在。

我不明白什么是错的，因为我有另一张桌子非常相似的帮手 -

    @Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_TABLE_SUBJECT = "CREATE TABLE IF NOT EXISTS " +
            TABLE_SUBJECT +
            "(" + KEY_ID + " Integer PRIMARY KEY AUTOINCREMENT, " +
            KEY_SUBJECT_NAME + " VARCHAR, " +
            KEY_CLASSROOM + " VARCHAR, " +
            KEY_TEACHER + " VARCHAR, " +
            KEY_COLOR + " Integer )";
    db.execSQL(CREATE_TABLE_SUBJECT);
}

public ArrayList<Subject> getAllSubjects() {
    ArrayList<Subject> subjects = new ArrayList<>();

    String query = "SELECT * FROM " + TABLE_SUBJECT;
    SQLiteDatabase db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery(query, null);

    Subject l;
    if (cursor.moveToFirst()) {
        do {
            l = new Subject();
            l.setId(Integer.parseInt(cursor.getString(0)));
            l.setName(cursor.getString(1));
            l.setClassroom(cursor.getString(2));
            l.setTeacher(cursor.getString(3));
            l.setColor(cursor.getInt(4));
            subjects.add(l);
        } while (cursor.moveToNext());
    }
    Log.d("getAllSubjects", subjects.toString());
    return subjects;
}

它没有任何问题。

日志如下 -

02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/SQLiteLog: (1) no 
such table: ClassTimes
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement D/AndroidRuntime: Shutting down VM
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime: FATAL EXCEPTION: main
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime: Process: com.anapp.tpb.replacement, PID: 1238
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.anapp.tpb.replacement/com.anapp.tpb.replacement.Setup.DataPresentation.ClassTimeCollector}: android.database.sqlite.SQLiteException: no such table: ClassTimes (code 1): , while compiling: SELECT  * FROM ClassTimes
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.app.ActivityThread.-wrap11(ActivityThread.java)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:148)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5417)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:  Caused by: android.database.sqlite.SQLiteException: no such table: ClassTimes (code 1): , while compiling: SELECT  * FROM ClassTimes
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:887)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:498)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1316)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1255)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at com.anapp.tpb.replacement.Storage.StorageHelpers.ClassTimeStorageHelper.getAllClasses(ClassTimeStorageHelper.java:111)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at com.anapp.tpb.replacement.Setup.DataPresentation.ClassTimeCollector.onCreate(ClassTimeCollector.java:87)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.app.Activity.performCreate(Activity.java:6237)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.app.ActivityThread.-wrap11(ActivityThread.java) 
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102) 
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:148) 
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5417) 
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method) 
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
02-20 19:59:58.370 1238-1238/com.anapp.tpb.replacement E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Answer 1

SQLiteOpenHelper用于版本化数据库文件，而不是表格。如果数据库中有多个表，请将它们全部放在同一个帮助程序中。
CREATE TABLE中存在语法问题。外键定义应该在末尾，而不是与列定义混合。
您有try - catch隐藏语法问题。去掉它。如果出现问题，onCreate()不能正常返回，但会抛出异常。
修复上述内容后，请再次卸载您的应用，以删除使用损坏的onCreate()创建的空数据库。

Answer 2

首先打开数据库，即SQLiteDatabase db = this.getWritableDatabase（）; 然后执行CRUD操作。

所以，改变

String query = "SELECT * FROM " + TABLE_CLASS_TIMES;
SQLiteDatabase db = this.getWritableDatabase();

                 to

SQLiteDatabase db = this.getWritableDatabase();
String query = "SELECT * FROM " + TABLE_CLASS_TIMES;

未调用Android SQLiteHelper OnCreate方法。导致没有这样的表异常

2 个答案: