Question

我有一个带有列“ Bunks”的SQLite，其值可以通过显示SQLite内容的recycleview递增或递减。当减小该值时，请将goint保持为负值。我想将值限制为0以上。我该如何实现？ mysqlitemethods：

public int getbunk(long id) {
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery("SELECT * FROM " + TABLE_NAME + " WHERE " + COLUMN_ID + " = " + String.valueOf(id), null);
        int output = -1;
        if (cursor != null) {
            if (cursor.moveToFirst()) {
                output = cursor.getInt(cursor.getColumnIndex(COL_3));
            }
            cursor.close();
        }
        return output;

    }
    public int updatebunk(long id){
        SQLiteDatabase db = this.getWritableDatabase();
        int bunk = getbunk(id);
        if (bunk<0){
            Log.i("error", "updatebunk:below 0 ");

        }
        int bunkinc= ++bunk;
        ContentValues contentValues= new ContentValues();
        contentValues.put(COL_3, bunkinc);
        db.update(TABLE_NAME,contentValues,COLUMN_ID+ "=?",new String[]{String.valueOf(id)});
        db.close();

        return bunkinc;
    }
    public int updatebunkdelete(long id){
        SQLiteDatabase db = this.getWritableDatabase();
        int bunk = getbunk(id);
        int bunkdec= --bunk;
        ContentValues contentValues= new ContentValues();
        contentValues.put(COL_3,bunkdec);
        db.update(TABLE_NAME,contentValues,COLUMN_ID+ "=?",new String[]{String.valueOf(id)});
        db.close();
        return bunkdec;
    }

用于增加和减少的myrecyclemethos：

 @Override
    public void onBindViewHolder(@NonNull attendence_recycleadapter.ViewHolder holder, final int position) {
        final attendence attendence= mattendence_list.get(position);

        holder.subname.setText("NAME: " + attendence.getSubname());
        holder.subcredit.setText("CREDIT: " + attendence.getCredit());
        holder.bunks.setText("BUNKS: " + attendence.getBunks());
        holder.deletesub.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Myhelper myhelper = new Myhelper(mcontext);
               myhelper.delete(attendence.getId(),mcontext);
               notifyItemRemoved(position);
               notifyItemRangeChanged(position,mattendence_list.size());
               notifyDataSetChanged();
                delete(position);
            }
        });
        holder.addbunk.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Myhelper myhelper = new Myhelper(mcontext);
                int newbunk = myhelper.updatebunk(attendence.getId());
               attendence.setBunks(newbunk);
               mattendence_list.set(position,attendence);
                notifyDataSetChanged();
                Toast.makeText(mcontext,"+1 class bunked",Toast.LENGTH_SHORT).show();
            }
        });
        holder.deletebunk.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Myhelper myhelper = new Myhelper(mcontext);
                int newbunk = myhelper.updatebunkdelete(attendence.getId());
                attendence.setBunks(newbunk);
                mattendence_list.set(position,attendence);
                notifyDataSetChanged();
                Toast.makeText(mcontext,"Bunk deleted",Toast.LENGTH_SHORT).show();
            }
        });
    }

初始值是0，用户可以递增或递减，如何阻止用户将值设为负数？

Answer 1

更改方法updatebunkdelete()：

public int updatebunkdelete(long id){
    int bunk = getbunk(id);
    int bunkdec= bunk - 1;

    if (bunkdec < 0) {
        return bunk;
    }

    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues contentValues= new ContentValues();
    contentValues.put(COL_3,bunkdec);
    db.update(TABLE_NAME,contentValues,COLUMN_ID+ "=?",new String[]{String.valueOf(id)});
    db.close();
    return bunkdec;
}

如何限制sqlite列的值变为负数？

1 个答案: