如何在Android中正确使用数据库？

I'm building an app that relies heavily on database usage. However, my emulator is behaving erratically and I can't find any pattern to what/when works and what/when it doesn't.

我正在构建一个严重依赖数据库使用的应用程序。但是,我的模拟器表现不正常,我找不到任何模式,什么/什么工作,什么/什么不工作。

Below you have my Adapter and Helper class taken straight from an example I found on the web. In this form, it functions perfectly, it adds records, deletes them, updates them and displays them in a list flawlessly.

下面我从我在网上找到的一个例子中直接看了我的Adapter和Helper类。在这种形式中,它完美地运行,它添加记录,删除它们,更新它们并在列表中完美地显示它们。

If I try and change ANYTHING (for example the KEY_TITLE value), the app crashes, even if I create a completely new emulator. I'm completely stumped by this and any help would be greatly welcomed...

如果我尝试更改ANYTHING(例如KEY_TITLE值),即使我创建了一个全新的模拟器,应用程序也会崩溃。我完全被这个困住了,任何帮助都会受到极大的欢迎......

public class PirelliDBAdapter {
private static final String DATABASE_NAME="data";
private static final String DATABASE_TABLE="reminders";
private static final int DATABASE_VERSION=1;

public static final String KEY_TITLE="title";
public static final String KEY_BODY="body";

public static final String KEY_LOCATION = "location";
public static final String KEY_TYPE = "type";

public static final String KEY_DATE_TIME="date_time_value";
public static final String KEY_ROW_ID="_id";

private DatabaseHelper mDbHelper;
private SQLiteDatabase db;

private static final String DATABASE_CREATE =
        "create table " + DATABASE_TABLE + " ( "+
                KEY_ROW_ID+ " integer primary key autoincrement, "+
                KEY_TITLE+ " text not null, "+
                KEY_BODY+" text not null, "+
                KEY_DATE_TIME+ " text not null);";

private Context mContext;

public PirelliDBAdapter(Context c){
    mContext=c;
}


// database open/close actions
public PirelliDBAdapter open() throws android.database.SQLException{
    mDbHelper=new DatabaseHelper(mContext);
    db=mDbHelper.getWritableDatabase();
    return this;
}

public void close(){
    mDbHelper.close();
}

// database CRUD operation
public long createReminder(String title, String body, String dateTime){
    ContentValues initialValues = new ContentValues();
    initialValues.put(KEY_TITLE, title);
    initialValues.put(KEY_BODY, body);
    initialValues.put(KEY_DATE_TIME, dateTime);

    return db.insert(DATABASE_TABLE, null, initialValues);

}

public boolean deleteReminder(long rowId){
    return db.delete(DATABASE_TABLE, KEY_ROW_ID+" = "+rowId,null) >0;
}

public Cursor fetchAllReminders(){
    return db.query(DATABASE_TABLE,new String [] {KEY_ROW_ID,KEY_TITLE,KEY_BODY,KEY_DATE_TIME}, null, null, null, null, null);
}

public Cursor fetchReminder(long rowId) throws SQLException{
    Cursor c = db.query(true, DATABASE_TABLE, new String []{KEY_ROW_ID,KEY_TITLE,KEY_BODY,KEY_DATE_TIME}, KEY_ROW_ID+" = "+rowId, null,null,null,null,null);

    if(c!=null){
        c.moveToFirst();
    }
    return c;
}

public boolean updateReminder(long rowId, String title, String body, String dateTime){
    ContentValues args = new ContentValues();
    args.put(KEY_TITLE, title);
    args.put(KEY_BODY, body);
    args.put(KEY_DATE_TIME, dateTime);

    return db.update(DATABASE_TABLE, args, KEY_ROW_ID+" = "+rowId, null)>0;
}

private static class DatabaseHelper extends SQLiteOpenHelper{
    public DatabaseHelper(Context c){
        // create the current database
        super(c,DATABASE_NAME,null,DATABASE_VERSION);
    }

    //  overrides

    @Override
    public void onCreate(SQLiteDatabase db) {
        // create the database table
        db.execSQL(DATABASE_CREATE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("drop table " + DATABASE_TABLE);
        db.execSQL(DATABASE_CREATE);

    }
}

Here's my error log when trying to add another field to the database (AFTER creating an entirely new AVD):

尝试将另一个字段添加到数据库时,这是我的错误日志(创建一个全新的AVD后):

    12-28 22:02:11.806: E/SQLiteDatabase(421):  at  android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:149)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at pirelli.app.dbadapter.PirelliDBAdapter.open(PirelliDBAdapter.java:44)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at pirelli.app.AdminSpinnerScreen.onCreate(AdminSpinnerScreen.java:329)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at android.app.Activity.performCreate(Activity.java:4397)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1048)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1779)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1831)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at android.app.ActivityThread.access$500(ActivityThread.java:122)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1024)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at android.os.Handler.dispatchMessage(Handler.java:99)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at android.os.Looper.loop(Looper.java:132)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at android.app.ActivityThread.main(ActivityThread.java:4123)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at java.lang.reflect.Method.invokeNative(Native Method)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at java.lang.reflect.Method.invoke(Method.java:491)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
    12-28 22:02:11.806: E/SQLiteDatabase(421):  at dalvik.system.NativeStart.main(Native Method)

2 个解决方案

#1

Are you perhaps installing over a previous install on the emulator? The database is only created once. After that, if you change a column name, it would not work.

您是否可以在模拟器上安装以前的安装?数据库仅创建一次。之后,如果更改列名称,则无效。

If you make a change to your database structure, you need to either clear the app from the device/emulator to force a fresh install or increment the version number. Of course, if you update the version number, you need to implement onUpgrade to destroy the database and recreate (or do the appropriate migrations).

如果对数据库结构进行了更改,则需要从设备/模拟器中清除应用程序以强制进行全新安装或增加版本号。当然,如果更新版本号,则需要实现onUpgrade以销毁数据库并重新创建(或执行适当的迁移)。

#2

I had to change the adapter class so whenever I make a change to the database, I use the commented lines below:

我不得不更改适配器类,所以每当我对数据库进行更改时,我都会使用下面的注释行:

public DatabaseHelper(Context c){
        // create the current database
        super(c,DATABASE_NAME,null,DATABASE_VERSION);
        SQLiteDatabase db = this.getWritableDatabase();
        try{//USE THESE WHEN CHANGING DB STRUCTURE
            //db.execSQL("drop table if exists " + DATABASE_TABLE);
            //db.execSQL(DATABASE_CREATE);
        } catch( Exception E ){
            Log.v("ERRRRRRROR", E.getMessage());
        }
    }

#1