Java 无法解析SQLiteOpenHelper中的方法onAttach()
我试图从扩展SQLiteOpenHelper的类调用一个方法(HomeFragment中的createButton)。我正在使用getSupportFragmentManager打开此片段,因此我需要传递上下文才能正确使用此getSupportFragmentManager。我尝试过以这种方式使用上下文:Java 无法解析SQLiteOpenHelper中的方法onAttach(),java,android,sqlite,android-fragments,Java,Android,Sqlite,Android Fragments,我试图从扩展SQLiteOpenHelper的类调用一个方法(HomeFragment中的createButton)。我正在使用getSupportFragmentManager打开此片段,因此我需要传递上下文才能正确使用此getSupportFragmentManager。我尝试过以这种方式使用上下文: private FragmentActivity myContext; @Override public void onAttach(Context context) { myCon
private FragmentActivity myContext;
@Override
public void onAttach(Context context) {
myContext=(FragmentActivity) context;
super.onAttach(context);
}
public void buttonCreator(Drawable d,String a) {
Log.d("tag_name", "buttonCreator" + myContext);
HomeFragment homeFragment = (HomeFragment)myContext.getSupportFragmentManager().getFragments().get(1);
homeFragment.createButton(d, a);
}
但是我在调用“super.onAttach(context)”时出错,无法解析方法onAttach()是否有一种方法可以在SQLiteOpenHelper中使用onAttach(),以便访问getSupportFragmentManager来打开我的片段?
我也尝试过以这种方式访问上下文:
但当我这样做时,它“无法解析方法'getSupportFragmentManager()'”
以下是完整的类代码:
public class DatabaseStructure extends SQLiteOpenHelper {
// Database Version
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "database";
// Table Names
private static final String DB_TABLE = "table_image";
// column names
private static final String KEY_NAME = "image_name";
private static final String KEY_IMAGE = "image_data";
// Table create statement
private static final String CREATE_TABLE_IMAGE = "CREATE TABLE " + DB_TABLE + "("+
KEY_NAME + " TEXT," +
KEY_IMAGE + " BLOB);";
private Context mContext;
public DatabaseStructure(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
Log.d("tag_name", "Entered DatabaseStructure" + context);
mContext = context;
}
@Override
public void onCreate(SQLiteDatabase db) {
// creating table
db.execSQL(CREATE_TABLE_IMAGE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// on upgrade drop older tables
db.execSQL("DROP TABLE IF EXISTS " + DB_TABLE);
// create new table
onCreate(db);
}
public void addEntry( String name, byte[] image) throws SQLiteException {
SQLiteDatabase db = this.getWritableDatabase();
Log.d("tag_name", "Enter Add Entry" + db);
ContentValues cv = new ContentValues();
cv.put(KEY_NAME, name);
cv.put(KEY_IMAGE, image);
db.insert(DB_TABLE, null, cv);
}
public boolean checkDatabase() {
Log.d("tag_name", "In CheckDatabase method" );
SQLiteDatabase db = this.getWritableDatabase();
Cursor mCursor = db.rawQuery("SELECT * FROM " + DB_TABLE, null);
if (mCursor.moveToFirst())
{
mCursor.moveToFirst();
String appName = mCursor.getString(0);
byte[] image = mCursor.getBlob(1);
Bitmap bitmap = BitmapFactory.decodeByteArray(image, 0, image.length);
Drawable d = new BitmapDrawable(Resources.getSystem(), bitmap);
//Drawable d = new BitmapDrawable(bitmap);
buttonCreator(d, appName);
return true;
} else
{
return false;
}
}
private FragmentActivity myContext;
@Override
public void onAttach(Context context) {
myContext=(FragmentActivity) context;
super.onAttach(context);
}
public void buttonCreator(Drawable d,String a) {
Log.d("tag_name", "buttonCreator" + myContext);
HomeFragment homeFragment = (HomeFragment)myContext.getSupportFragmentManager().getFragments().get(1);
homeFragment.createButton(d, a);
}
}
onAttach()
是Fragment
的回调方法,您可以重写该方法来附加侦听器或Fragment类中的其他内容
根据您所说的,您从SQLiteOpenHelper
扩展了类,因此您没有任何onAttach()
方法可以重写。
那么答案是什么呢
是否有一种方法可以在SQLiteOpenHelper
中使用onAttach(),以便
访问getSupportFragmentManager以打开我的片段
--
否
另外,关于如何获取上下文,我不知道为什么要将类扩展到
SQLiteOpenHelper
,但是如果要获取上下文来启动片段或使用getSupportFragmentManager()
,您可以在创建其对象时在该类中传递上下文。我完全不了解此代码与SQLiteOpenHelper
的关系。你能发布完整的课程吗?只需删除本主题不需要的方法。为什么要从一个只负责管理数据库的类中执行与视图相关的操作?通常情况下是相反的。@ghostman我发布了完整的活动,它扩展了SQLiteOpenHelper。@Natalieжжжжжжжжжжжжжжжжа。然后我想检查数据库是否为空。如果它不是空的,我想打开一个新的活动,并将存储在数据库中的值传递给它。有没有更好的方法呢?谢谢你的反馈。您说“当您创建该类的对象时,您可以在该类中传递上下文”。但我怎样才能传递context,这样我就不会得到context=null?您已经运行了activity,从中获得了context,但是当您的片段被附加时,您应该打开数据库连接。使用Loader在后台处理数据库的最佳方法。
public class DatabaseStructure extends SQLiteOpenHelper {
// Database Version
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "database";
// Table Names
private static final String DB_TABLE = "table_image";
// column names
private static final String KEY_NAME = "image_name";
private static final String KEY_IMAGE = "image_data";
// Table create statement
private static final String CREATE_TABLE_IMAGE = "CREATE TABLE " + DB_TABLE + "("+
KEY_NAME + " TEXT," +
KEY_IMAGE + " BLOB);";
private Context mContext;
public DatabaseStructure(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
Log.d("tag_name", "Entered DatabaseStructure" + context);
mContext = context;
}
@Override
public void onCreate(SQLiteDatabase db) {
// creating table
db.execSQL(CREATE_TABLE_IMAGE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// on upgrade drop older tables
db.execSQL("DROP TABLE IF EXISTS " + DB_TABLE);
// create new table
onCreate(db);
}
public void addEntry( String name, byte[] image) throws SQLiteException {
SQLiteDatabase db = this.getWritableDatabase();
Log.d("tag_name", "Enter Add Entry" + db);
ContentValues cv = new ContentValues();
cv.put(KEY_NAME, name);
cv.put(KEY_IMAGE, image);
db.insert(DB_TABLE, null, cv);
}
public boolean checkDatabase() {
Log.d("tag_name", "In CheckDatabase method" );
SQLiteDatabase db = this.getWritableDatabase();
Cursor mCursor = db.rawQuery("SELECT * FROM " + DB_TABLE, null);
if (mCursor.moveToFirst())
{
mCursor.moveToFirst();
String appName = mCursor.getString(0);
byte[] image = mCursor.getBlob(1);
Bitmap bitmap = BitmapFactory.decodeByteArray(image, 0, image.length);
Drawable d = new BitmapDrawable(Resources.getSystem(), bitmap);
//Drawable d = new BitmapDrawable(bitmap);
buttonCreator(d, appName);
return true;
} else
{
return false;
}
}
private FragmentActivity myContext;
@Override
public void onAttach(Context context) {
myContext=(FragmentActivity) context;
super.onAttach(context);
}
public void buttonCreator(Drawable d,String a) {
Log.d("tag_name", "buttonCreator" + myContext);
HomeFragment homeFragment = (HomeFragment)myContext.getSupportFragmentManager().getFragments().get(1);
homeFragment.createButton(d, a);
}
}