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Я хочу прочитать все данные (folder_id =1 в качестве примера) из моей таблицы базы данных.

Примечание:- Folder_id-это столбец, в котором хранится идентификатор папки из таблицы папок в folder.db, которая является другой базой данных folder_id, не генерируется базой данных notes.db

Можно ли это сделать, не слишком сильно меняя код, как я могу этого добиться? Я попытался найти ответ в гугле, но не смог найти ни одного подходящего ответа. вот почему я спрашиваю здесь

вот мой вспомогательный класс базы данных:-

 public class MyNotesDatabaseHelper extends SQLiteOpenHelper
{

 //create a context object that will help us to point to this MyDatabaseHelper class      


private Context context;

//Constants
//database name
private static final String DATABASE_NAME = "Notes_collection.db";
private static final int DATABASE_VERSION = 1;

//table name
public static final String  TABLE_NAME = "my_notes";

//creating columns names
private static final String COLUMN_ID = "notes_id";
private static final String COLUMN_FOLDER_ID  ="folder_id";
private static final String COLUMN_NOTE_TITLE ="note_title";
private static final String COLUMN_NOTE_CONTENT ="note_content";

public MyNotesDatabaseHelper(@Nullable Context context)
{
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
    this.context = context;
}
 @Override
public void onCreate(SQLiteDatabase db) {
    //query is holding the sql statement needed for the operation
    //be sure to add spaces and follow the syntax otherwise it may cause issue
    String query = "CREATE TABLE "   TABLE_NAME  
            " ("   COLUMN_ID   " INTEGER PRIMARY KEY AUTOINCREMENT, "  
            COLUMN_FOLDER_ID  " INTEGER, "  
            COLUMN_NOTE_TITLE   " TEXT, "  
            COLUMN_NOTE_CONTENT   " TEXT " ")" ;
    db.execSQL(query);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS "  TABLE_NAME);
    //whenever we upgrade our database we need to call our oncreate method as well
    onCreate(db);
}
void addNote(Integer folder_id_String,String Note_name,String Note_content)
{
    //create a sql Lite database object
    //this will refer to our SQLiteOpenHelper class
    //getWritableDatabase() will help us to write to our table
    SQLiteDatabase db = this.getWritableDatabase();
    //ContentValues cv will store all our data from our application and will pass this to our database table
    ContentValues cv = new ContentValues();
    //cv.put(key:"column name",value:"Data")
    cv.put(COLUMN_FOLDER_ID,folder_id_String);
    cv.put(COLUMN_NOTE_TITLE,Note_name);
    //the folder detail will contain the notes_id which will come from another database
    cv.put(COLUMN_NOTE_CONTENT,Note_content);

    //now we will insert the data inside our database using our SQLite object db
    long result = db.insert(TABLE_NAME,null,cv);

    if(result == -1) //our application failed to insert the data
    {
        Toast.makeText(context,"Err Bad Protocol A113 0007287197x6211963H!",Toast.LENGTH_SHORT).show();
    }
    else //our application sucessfully inserted the data from our app to our database
    {
        Toast.makeText(context,"Added Successfully!",Toast.LENGTH_SHORT).show();
    }
}
Cursor ReadAllData()
{

    //db.rawQuery("SELECT name,address FROM mytable WHERE name = 'Fred'");
    //it will select all the names called Fred

    //selecting all the data from our database table
    String query = "SELECT * FROM "  TABLE_NAME;
    //creaing an sql database object and get readable database this time
    SQLiteDatabase db = this.getReadableDatabase();
    //creating a cursor object
    Cursor cursor = null;
    if(db!=null)
    {
        cursor = db.rawQuery(query,null);
    }
    return cursor;
}}
 

вот мой пользовательский класс адаптера:-

 public class NotesCustomAdapter extends RecyclerView.Adapter<NotesCustomAdapter.MyViewHolder>


{
    private Context context;
    private ArrayList note_id_CustomAdapter, folder_id_CustomAdapter,
    note_title_CustomAdapter,note_content_CustomAdapter;

//item position index in our recylerView
int position;

//create an activity object so that we can refresh our recyclerView in our application
Activity activity;

//custom Adapter constructor should have a context and four different arrayList
//because when we initialize this class inside our main activity
//we want to pass all these array list that we have already created in our MainActivity
NotesCustomAdapter(Activity activity,Context context , ArrayList note_id,ArrayList folder_id, ArrayList note_title,ArrayList note_content)
{
    //refreshing our Main activity RecyclerView with new data
    this.activity = activity;

    //setting up the parameter variable of this constructor to our global variable of this class
    //so we can access these objects in our full class
    this.context = context;
    this.note_id_CustomAdapter = note_id;
    this.folder_id_CustomAdapter = folder_id;
    this.note_title_CustomAdapter = note_title;
    this.note_content_CustomAdapter = note_content;
}

 @NonNull
@Override
public NotesCustomAdapter.MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    //we will be infating our row layout for our RecyclerView
    LayoutInflater inflater = LayoutInflater.from(context);
    View view =  inflater.inflate(R.layout.note_list_card_view,parent,false);
    return new MyViewHolder(view);
}

@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
    this.position = position;
    //getting data from arrays and setting the data to our textView that is present in row Layout for our RecylerView
    //here we are going to set Text into these textView's
    holder.note_id__note_card_view_layout.setText(String.valueOf(note_id_CustomAdapter.get(position)));
    holder.folder_id_note_row.setText(String.valueOf(folder_id_CustomAdapter.get(position)));
    holder.note_title_note_card_view_layout.setText(String.valueOf(note_title_CustomAdapter.get(position)));
    holder.note_content_id_row.setText(String.valueOf(note_content_CustomAdapter.get(position)));

    //ad onclick listener on recylerView items
    //setting up the onclick Listener for our mainlayout
    holder.note_card_view_layout.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(context,ViewNoteContentActivity.class);
            //sending data to View activity via intent
            intent.putExtra("note_id",String.valueOf(note_id_CustomAdapter.get(position)));
            intent.putExtra("folder_id",String.valueOf(folder_id_CustomAdapter.get(position)));
            intent.putExtra("note_title",String.valueOf(note_title_CustomAdapter.get(position)));
            intent.putExtra("note_content",String.valueOf(note_content_CustomAdapter.get(position)));
            //refreshing our Main activity recylerView with updated data
            activity.startActivityForResult(intent,1);
            //activity transition animation
            activity.overridePendingTransition(R.anim.slide_in_left, R.anim.nothing);
        }
    });

    //add onlong click listener on recyclerview items

    //setting up the onclick Listener for our mainlayout
    holder.note_card_view_layout.setOnLongClickListener(new View.OnLongClickListener() {
        @Override
        public boolean onLongClick(View v) {
            // go to update Folder name Activity when the item is long pressed in the main activity
            Intent intent2 = new Intent(context,NoteUpdateActivity.class);
            //sending data to View activity via intent
            intent2.putExtra("note_id",String.valueOf(note_id_CustomAdapter.get(position)));
            intent2.putExtra("folder_id",String.valueOf(folder_id_CustomAdapter.get(position)));
            intent2.putExtra("note_title",String.valueOf(note_title_CustomAdapter.get(position)));
            intent2.putExtra("note_content",String.valueOf(note_content_CustomAdapter.get(position)));
            //refreshing our Main activity recylerView with updated data
            activity.startActivityForResult(intent2,1);
            //activity transition animation
            activity.overridePendingTransition(R.anim.slide_in_left, R.anim.nothing);
            return true;
        }
    });
}

@Override
public int getItemCount() {
    return note_id_CustomAdapter.size();
}

public class MyViewHolder extends RecyclerView.ViewHolder{
    TextView note_title_note_card_view_layout; //holds the title of a note
    TextView note_id__note_card_view_layout; //holds the id of the note from note.db
    TextView folder_id_note_row; //holds the folder_id
    TextView note_content_id_row; //will hold the contents of the note

    // calling our mainlayout from our recycler_view_row.xml file
    ConstraintLayout note_card_view_layout;
    public MyViewHolder(@NonNull View itemView) {
        super(itemView);
        //now getting the id's of those textView's
        note_title_note_card_view_layout = itemView.findViewById(R.id.note_title_note_card_view_layout);
        note_id__note_card_view_layout = itemView.findViewById(R.id.note_id__note_card_view_layout);
        folder_id_note_row = itemView.findViewById(R.id.folder_id_note_row);
        note_content_id_row = itemView.findViewById(R.id.note_content_id_row);

        // binding our mainlayout from our recycler_view_row.xml file to CustomAdapter class
        note_card_view_layout = itemView.findViewById(R.id.note_card_view_layout);
    }
}
}
 

here is my java activity class:-

 public class ViewFolderContentsActivity extends AppCompatActivity {

//creating an object of MyDatabaseHelper Class
MyNotesDatabaseHelper notesdb;

//NotesCustomAdapter
NotesCustomAdapter NotesCustomAdapter;

//now create an array list to hold the list of note_id,folder_id,note_title,note_content
ArrayList<String> note_id,folder_id,note_title,note_content;

//related to folder.db
String folder_id_String,folder_name_String,folder_content_String;

FloatingActionButton Add_Button_view_folder_content_activity ;
RecyclerView recylerView_view_folder_content_activity;

ImageView empty_imageView_view_folder_content_activity;
TextView textView_view_folder_content_activity;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_view_folder_contents);

    Add_Button_view_folder_content_activity = findViewById(R.id.Add_Button_view_folder_content_activity);
    recylerView_view_folder_content_activity = findViewById(R.id.recylerView_view_folder_content_activity);
    empty_imageView_view_folder_content_activity = findViewById(R.id.empty_imageView_view_folder_content_activity);
    textView_view_folder_content_activity = findViewById(R.id.textView_view_folder_content_activity);

    //making the textView invisible
    textView_view_folder_content_activity.setVisibility(View.INVISIBLE);
    //making th imageView invisible
    empty_imageView_view_folder_content_activity.setVisibility(View.INVISIBLE);

    // calling the action bar
    ActionBar actionBar = getSupportActionBar();

    // showing the back button in action bar
    actionBar.setDisplayHomeAsUpEnabled(true);

    //First call this
    //this function gets data from the main activity holding the list of folders
    getIntentDataFromCustomAdapter();

    //setting up the title of the activity
    actionBar.setTitle(folder_name_String);

  //add an onclick listener on the floating add button
    Add_Button_view_folder_content_activity.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            //open AddNote Activity
            Intent intent = new Intent(ViewFolderContentsActivity.this, AddNoteActivity.class);
            //send the folder_id_String via intent to Add note activity
            intent.putExtra("folder_id",folder_id_String);
            startActivity(intent);
            //activity transition animation
            overridePendingTransition(R.anim.slide_in_left, R.anim.nothing);

        }
    });

    notesdb = new MyNotesDatabaseHelper(ViewFolderContentsActivity.this);
    note_id =  new ArrayList<>();
    folder_id =  new ArrayList<>();
    note_title =  new ArrayList<>();
    note_content = new ArrayList<>();

    //calling StoreDataInArrays() function
    StoreDataInArrays();

    //debugging
    Log.i("folder_id_array", String.valueOf(folder_id));

    //initialize our custom Adapter object
    /*
    customAdapter = new CustomAdapter(activity: MainActivity.this,context: this,book_id,book_title,book_author,book_page);
    the above line will refresh the recylerView in our main Activity by updating the incoming data from CustomAdapter class
     */
    NotesCustomAdapter = new NotesCustomAdapter(ViewFolderContentsActivity.this,this,note_id,folder_id,note_title,note_content);
    recylerView_view_folder_content_activity.setAdapter(NotesCustomAdapter);
    recylerView_view_folder_content_activity.setLayoutManager(new LinearLayoutManager(ViewFolderContentsActivity.this));
}

void StoreDataInArrays()
{
    //calling ReadAllData() method or function from MyDatabaseHelper class
    Cursor cursor = notesdb.ReadAllData();
    if(cursor.getCount() == 0) //that means there is no data
    {
        empty_imageView_view_folder_content_activity.setVisibility(View.VISIBLE);
        textView_view_folder_content_activity.setVisibility(View.VISIBLE);
    }
    else
    {
        //move the cursor to the next position in the table
        //adding data from our database to our arrays
        while(cursor.moveToNext())
        {
                note_id.add(cursor.getString(0));
                folder_id.add(cursor.getString(1));
                note_title.add(cursor.getString(2));
                note_content.add(cursor.getString(3));
            }


    }
}// DisplayData function closed

//get data from the CustomAdapter Layout via intent
//this function gets data from the main activity holding the list of folders
void getIntentDataFromCustomAdapter()
{
    if(getIntent().hasExtra("id") amp;amp; getIntent().hasExtra("folder_name") amp;amp; getIntent().hasExtra("folder_content"))
    {
        //get data from CustomAdapter class via Intent
        folder_id_String = getIntent().getStringExtra("id");
        folder_name_String = getIntent().getStringExtra("folder_name");
        folder_content_String = getIntent().getStringExtra("folder_content");

        //setting data to the editText
        Log.i("folder_id",folder_id_String);
        Log.i("folder_name",folder_name_String);
    }
    else
    {
        Toast.makeText(this,"No data Err A113 000x2273821",Toast.LENGTH_SHORT).show();
    }
}

// this event will enable the back activity action bar back button
// function to the button on press activity action bar back button
@Override
public boolean onOptionsItemSelected(@NonNull MenuItem item) {
    switch (item.getItemId()) {
        case android.R.id.home:
            this.finish();
            overridePendingTransition(R.anim.nothing, R.anim.slide_out_right);
            return true;
    }
    return super.onOptionsItemSelected(item);
}

//this method handles back button of android os
@Override
public void onBackPressed() {
    super.onBackPressed();
    finish();
    overridePendingTransition(R.anim.nothing, R.anim.slide_out_right);

}

//refreshing the recylerView in our main activity with new data when mainActivity restarts
@Override
protected void onRestart() {
    super.onRestart();
    recreate();
}
}