一個專案，通常會有些後門。這些後門常有不勘入耳的原因(防止業主過河拆橋)，也有很富麗堂皇的理由(防止被入侵時的緊急關閉)。不論你是正派還是反派，一定都會有後門。本篇不會描述整個後門的過程，僅說明其中一部份，就是資料庫的更改。

下圖為本例之圖示，當按下某一專案的Switch, 那個專案立即全面停用

MainActivity.kt

import android.os.Bundle
import android.os.Handler
import android.os.Looper
import android.view.View
import android.widget.AdapterView
import android.widget.Switch
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
import java.lang.ref.WeakReference
import java.sql.DriverManager

val LIST_REFRESH = 10000

class MainActivity : AppCompatActivity() {
    var listViewData=ArrayList<Map<String, String>>()
    var listViewAdapter:ViewAdapter ? =null
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        Class.forName("com.mysql.jdbc.Driver")
        listViewAdapter= ViewAdapter(this, listViewData)
        listView.adapter=listViewAdapter
        listView.setOnItemClickListener(listViewClick)
        Thread{
            val conn=DriverManager.getConnection(G.connStr, G.dbAccount, G.dbPassword)
            var cmd="select * from project"
            var stm=conn.createStatement()
            var rs=stm.executeQuery(cmd)
            while (rs.next()){
                var map=HashMap<String, String>()
                map.put("id", rs.getString(1))
                map.put("project", rs.getString(2))
                map.put("enabled", rs.getString(3))
                listViewData.add(map)
            }
            rs.close()
            conn.close()
            handler.sendEmptyMessage(LIST_REFRESH)
        }.start()
    }

    var listViewClick = object : AdapterView.OnItemClickListener {
        override fun onItemClick(parent: AdapterView<*>?, view: View?, position: Int, id: Long) {
            if (view ==null) return //底下的view及sw就不用再加 "?"了
            val sw = view.findViewById<Switch>(R.id.swEnabled)
            sw.isChecked = !sw.isChecked
            val id = view.findViewById<TextView>(R.id.txtId)?.text.toString().toInt()
            val enabled=if(sw.isChecked)1 else 0
            Thread {
                val conn = DriverManager.getConnection(G.connStr, G.dbAccount, G.dbPassword)
                var cmd = "update project set enabled=? where id=?"
                var stm=conn.prepareStatement(cmd)
                stm.setInt(1, enabled)
                stm.setInt(2, id)
                stm.execute()
                conn.close()
            }.start()
        }
    }
    val handler = Handler(
        Looper.myLooper()!!, WeakReference(Handler.Callback {
            when (it.what) {
                LIST_REFRESH -> {
                    listViewAdapter?.notifyDataSetChanged()
                }
            }
            false
        }).get()
    )
}

ViewAdapter.kt