Какой код я должен написать, чтобы удалить все карты в Kotlin? (Android Студия, Kotlin, SQlite)

Question

• MainActivity

package com.example.sqllite

class MainActivity : AppCompatActivity() {

lateinit var lists:ArrayList<Subject>
lateinit var DB:SQHelper
lateinit var data:Cursor


override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

 /*   val deletebtn = findViewById<Button>(R.id.btnDelete)

    deletebtn.setOnClickListener {
        deletedata
    } */

    val go = findViewById<Button>(R.id.btnGoSub)

    go.setOnClickListener {
        startActivity(Intent(this@MainActivity, AddSubject::class.java))
    }


    lists = ArrayList<Subject>()
    DB = SQHelper(applicationContext)
    data = DB.data_getter

    val adapter = Adapter(applicationContext, lists)
    val recyclerView = findViewById<RecyclerView>(R.id.list)

    ShowData()

    list.layoutManager = GridLayoutManager(applicationContext,2)
    list.adapter = adapter
 }


 fun ShowData() {

        if (data.count == 0){
            Toast.makeText(applicationContext,"There is no items",Toast.LENGTH_SHORT).show()
        }
        while (data.moveToNext())

            lists.add(Subject(data.getString(0),
                data.getString(1),
                data.getString(2)

            ))

    }

override fun onStart() {
    super.onStart()
    ShowData()
}

}

• SQHelper

  пакет com.example.sqllite

  класс SQHelper (context: Context): SQLiteOpenHelper (context, DB_name, null, 1) {

  переопределить fun onCreate (db: SQLiteDatabase?) {db? .exe cSQL ("создать таблицу $ TB_name (ID INTEGER PRIMARY KEY AUTOINCREMENT, S_title TEXT, S_title c TEXT) ")}

  переопределить fun onUpgrade (db: SQLiteDatabase ?, oldVersion: Int, newVersion: Int) {db? .Exe cSQL («DROP TABLE, ЕСЛИ СУЩЕСТВУЕТ $ TB_name»)

  }

  fun ADD_DATA (title_text: String, desc_text: String) {

  val DB = this.writableDatabase
  val values = ContentValues()
  values.put(title,title_text)
  values.put(desc, desc_text)
  
  DB.insert(TB_name,null, values )
  

  }

  fun delete_data (id: String): Int {

  val DB = this.writableDatabase
  val item = DB.delete(TB_name,"id = ?", arrayOf(id))
  
  return item
  

  }

  / * fun deleteTask (_id: Int): Boolean {val db = this.writableDatabase val _success = db.delete (TB_name, ID + "=?", arrayOf (_id.toString ())). toLong () db.close () return Integer.parseInt ("$ _ success")! = -1} * /

  val data_getter: Cursor get () {val DB = this.writableDatabase var d ata = DB.rawQuery ("выберите * из" + TB_name, null)

  return data
  

  }

  сопутствующий объект {var DB_name = "subjects.db" var TB_name = "Subjects" var id = "id" var title = "S_title" var des c = "S_des c"}

  }

  • Адаптер

  пакет com.example.sqllite

  Адаптер класса (var context: Context, data: ArrayList): RecyclerView.Adapter () {

  var data: List

  init {this .data = data}

  переопределить fun onCreateViewHolder (parent: ViewGroup, viewType: Int): ViewHolder {val layout = LayoutInflater.from (context) .inflate (R.layout.item_subject, parent, false) вернуть ViewHolder (макет)}

  переопределить забаву onBindViewHolder (holder: ViewHolder, position: Int) {holder.title.text = data [position] .title holder.des c .text = data [position] .desc holder.id.text = data [position] .id holder.btndel.setOnClickListener {position}

  }

  override fun getItemCount (): Int {return data.size} * 106 1 *

  class ViewHolder (item: View): RecyclerView.ViewHolder (item) {var title: TextView var id: TextView var des c: TextView var btndel: Button

  init {
      title = item.findViewById(R.id.titleTextv)
      id = item.findViewById(R.id.titleTextv2)
      desc = item.findViewById(R.id.descTextv)
      btndel = item.findViewById(R.id.btnDelete)
  }
  

  }

  }

• AddSubject

  пакет com.example.sqllite

  class AddSubject: AppCompatActivity () {

  переопределить fun onCreate (saveInstanceState: Bundle?) {super.onCreate (saveInstanceState) setContentView (R.layout.activity_add_subject)

  val DB = SQHelper(applicationContext)
  
  val title_input = findViewById<EditText>(R.id.editTitle)
  val desc_input = findViewById<EditText>(R.id.editDesc)
  val addbtn = findViewById<Button>(R.id.btnAdd)
  
  addbtn.setOnClickListener {
  
      val title_text = title_input.text.toString().trim()
      val desc_text = desc_input.text.toString().trim()
  
      DB.ADD_DATA(title_text,desc_text)
      Toast.makeText(this@AddSubject,"The Subject has been added",Toast.LENGTH_SHORT).show()
      startActivity(Intent(this@AddSubject,MainActivity::class.java))
  
  }
  

  }}

• activity_main. xml

• item_subject. xml

  <LinearLayout
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:layout_margin="10dp"
      android:orientation="vertical"
      android:padding="15dp">
  
      <TextView
          android:id="@+id/titleTextv2"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:gravity="center"
          android:text="@string/_1"
          android:textColor="#FFFFFF"
          android:textSize="18sp" />
  
      <TextView
          android:id="@+id/titleTextv"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:layout_gravity="center|center_horizontal|center_vertical"
          android:gravity="center|center_horizontal|center_vertical"
          android:text="@string/android"
          android:textColor="#FFFFFF"
          android:textSize="18sp" />
  
      <TextView
          android:id="@+id/descTextv"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_gravity="center|center_horizontal|center_vertical"
          android:gravity="center|center_horizontal|center_vertical"
          android:text="@string/learn_android"
          android:textColor="#FFFFFF"
          android:textSize="18sp" />
  
      <Button
          android:id="@+id/btnDelete"
          android:layout_width="100dp"
          android:layout_height="45dp"
          android:layout_gravity="center_horizontal"
          android:layout_marginTop="15dp"
          android:background="@drawable/buttonstyle"
          android:gravity="center"
          android:text="@string/delete"
          android:textAllCaps="false"
          android:textColor="#FFFFFF" />
  
  </LinearLayout>
  

• activity_add_subject

  <EditText
      android:id="@+id/editTitle"
      android:layout_width="wrap_content"
      android:layout_height="40dp"
      android:layout_gravity="center_horizontal"
      android:layout_marginTop="100dp"
      android:background="@android:color/background_dark"
      android:ems="10"
      android:hint="Enter your title"
      android:inputType="textPersonName"
      android:textColor="#FFFFFF"
      android:textColorHint="#FFFFFF"
      android:textSize="24sp" />
  
  <EditText
      android:id="@+id/editDesc"
      android:layout_width="wrap_content"
      android:layout_height="40dp"
      android:layout_gravity="center_horizontal"
      android:layout_marginTop="10dp"
      android:background="@android:color/background_dark"
      android:ems="10"
      android:hint="Enter your description"
      android:inputType="textPersonName"
      android:textColor="#FFFFFF"
      android:textColorHint="#FFFFFF"
      android:textSize="24sp" />