Detailed explanation of the code to implement work management Gantt chart effects based on Android

val x = leftPadding + i * (timeSpanPerTick / timeSpan) * viewWidth
(x, 0f, x, headerHeight, axisPaint)
(formatTime(minTime + i * timeSpanPerTick), x, textY, textPaint)

// --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------/*
 plugins {
     id ''
     id 'kotlin-android'
     id 'kotlin-kapt'
 }
 android {
     compileSdkVersion 34
     defaultConfig {
         applicationId ""
         minSdkVersion 21
         targetSdkVersion 34
         versionCode 1
         versionName "1.0"
     }
     buildFeatures { viewBinding true }
 }
 dependencies {
     implementation ":core-ktx:1.10.1"
     implementation ":appcompat:1.7.0"
     implementation ":material:1.9.0"
     implementation ":constraintlayout:2.1.4"
     implementation ":recyclerview:1.3.1"
     implementation ":lifecycle-viewmodel-ktx:2.6.1"
     implementation ":lifecycle-livedata-ktx:2.6.1"
     implementation ":room-runtime:2.5.2"
     kapt ":room-compiler:2.5.2"
     implementation ":threetenbp:1.6.0" // or ThreeTenABP
     implementation ":threetenabp:1.4.4"
 }
 */
 
// ---------------- document:  ----------------package 
 
import 
import 
import 
import 
 
/**
  * Task: Room entity, representing a task in the Gantt chart
  */
@Entity(tableName = "tasks")
data class Task(
    @PrimaryKey(autoGenerate = true) val id: Long = 0,
    val name: String,
    val startTime: Long, // millisecond timestamp    val endTime: Long,
    val color: Int // ARGB color)
 
// ---------------- document:  ----------------package 
 
import 
import .*
 
/**
  * TaskDao: Task addition, deletion, modification and search interface
  */
@Dao
interface TaskDao {
    @Query("SELECT * FROM tasks ORDER BY startTime")
    fun getAllTasks(): LiveData<List<Task>>
 
    @Insert(onConflict = )
    suspend fun insert(task: Task)
 
    @Delete
    suspend fun delete(task: Task)
}
 
// ---------------- document:  ----------------package 
 
import 
import 
 
/**
  * AppDatabase: Room database
  */
@Database(entities = [Task::class], version = 1)
abstract class AppDatabase : RoomDatabase() {
    abstract fun taskDao(): TaskDao
}
 
// ---------------- document:  ----------------package 
 
import 
import .*
import 
import 
import 
import 
 
/**
  * GanttViewModel: Holds a task list, provides addition, deletion, modification and check
  */
class GanttViewModel(application: Application) : AndroidViewModel(application) {
    private val db = (application, AppDatabase::, "").build()
    private val dao = ()
 
    val tasks: LiveData<List<Task>> = ()
 
    fun addTask(task: Task) =  {
        (task)
    }
 
    fun deleteTask(task: Task) =  {
        (task)
    }
}
 
// ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------<?xml version="1.0" encoding="utf-8"?>
< 
    xmlns:andro
    xmlns:app="/apk/res-auto"
    android:layout_width="match_parent" android:layout_height="match_parent">
 
    <!-- List of task names on the left -->
    <
        android:
        android:layout_width="120dp" android:layout_height="0dp"
        app:layout_constraintTop_toTopOf="parent" app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"/>
 
    <!-- Gantt chart area on the right，Roll horizontally -->
    <HorizontalScrollView
        android:
        android:layout_width="0dp" android:layout_height="0dp"
        android:scrollbars="none"
        app:layout_constraintTop_toTopOf="parent" app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toEndOf="@id/rvTasks" app:layout_constraintEnd_toEndOf="parent">
 
        <
            android:
            android:layout_width="wrap_content" android:layout_height="match_parent"/>
 
    </HorizontalScrollView>
 
    <!-- Add task button -->
    <
        android:
        android:layout_width="wrap_content" android:layout_height="wrap_content"
        app:srcCompat="@android:drawable/ic_input_add"
        app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent"
        android:layout_margin="16dp"/>
</>
 
// --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:andro
    android:
    android:layout_width="match_parent" android:layout_height="48dp"
    android:gravity="center_vertical"
    android:paddingStart="8dp"
    android:textSize="16sp"
    android:textColor="#333"/>
 
// ---------------- document:  ----------------package 
 
import 
import 
import 
import 
import 
import 
import 
 
/**
  * TaskNameAdapter: List of task names on the left
  */
class TaskNameAdapter : ListAdapter<Task, >(DIFF) {
    companion object {
        val DIFF = object : <Task>() {
            override fun areItemsTheSame(old: Task, new: Task) =  == 
            override fun areContentsTheSame(old: Task, new: Task) = old == new
        }
    }
    inner class NameVH(val binding: ItemTaskNameBinding) : ()
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) =
        NameVH(((), parent, false))
    override fun onBindViewHolder(holder: NameVH, position: Int) {
         = getItem(position).name
    }
}
 
// ---------------- document:  ----------------package 
 
import 
import .*
import 
import .*
import 
import 
import 
import 
import 
import 
 
/**
  * GanttChartView: Custom Gantt Chart View
  */
class GanttChartView @JvmOverloads constructor(
    context: Context, attrs: AttributeSet? = null
): View(context, attrs), ,  {
 
    // data    private var tasks: List<Task> = emptyList()
    private var minTime = Long.MAX_VALUE
    private var maxTime = 0L
    private var timeSpan = 1L // ms
 
    // Paintbrush    private val barPaint = Paint(Paint.ANTI_ALIAS_FLAG)
    private val axisPaint = Paint(Paint.ANTI_ALIAS_FLAG).apply { color = ; strokeWidth=2f }
    private val textPaint = Paint(Paint.ANTI_ALIAS_FLAG).apply { color = ; textSize = 24f }
 
    // Layout parameters    private val rowHeight = 80f
    private val headerHeight = 80f
    private var scaleFactor = 1f
    private var offsetX = 0f
 
    // Gestures    private val scroller = OverScroller(context)
    private val gestureDetector = GestureDetector(context, this)
    private val scaleDetector = ScaleGestureDetector(context, this)
 
    init {
         = 
    }
 
    /** Set tasks externally and recalculate the range */
    fun setTasks(list: List<Task>) {
        tasks = list
        if (()) {
            minTime =  {  }
            maxTime =  {  }
            timeSpan = maxTime - minTime
        }
        invalidate()
    }
 
    override fun onDraw(canvas: Canvas) {
        (canvas)
        if (()) return
 
        // 1. Draw the timeline        val totalWidth = () * scaleFactor
        val tickCount = 6
        for (i in 0..tickCount) {
            val x = offsetX + i / () * totalWidth
            (x, 0f, x, headerHeight, axisPaint)
            val time = minTime + i / () * timeSpan
            val label = (time)
                .atZone(()).toLocalDate().toString()
            (label, x + 10, headerHeight - 20, textPaint)
        }
 
        // 2. Draw each row of task bars         { idx, task ->
            val top = headerHeight + idx * rowHeight
            val bottom = top + rowHeight * 0.6f
            // Calculate left and right            val left = offsetX + ( - minTime) / () * totalWidth
            val right = offsetX + ( - minTime) / () * totalWidth
             = 
            (left, top + 10, right, bottom, barPaint)
        }
    }
 
    // ================== Gestures and zoom =======================    override fun onTouchEvent(event: MotionEvent): Boolean {
        (event)
        if (!) {
            (event)
        }
        return true
    }
    override fun onScale(detector: ScaleGestureDetector): Boolean {
        scaleFactor *= 
        scaleFactor = (0.5f, 3f)
        invalidate()
        return true
    }
    override fun onScaleBegin(detector: ScaleGestureDetector) = true
    override fun onScaleEnd(detector: ScaleGestureDetector) {}
    override fun onDown(e: MotionEvent) = true
    override fun onShowPress(e: MotionEvent) {}
    override fun onSingleTapUp(e: MotionEvent) = false
    override fun onScroll(e1: MotionEvent, e2: MotionEvent, dx: Float, dy: Float): Boolean {
        offsetX -= dx
        offsetX = (-(), () * scaleFactor)
        invalidate()
        return true
    }
    override fun onLongPress(e: MotionEvent) {}
    override fun onFling(e1: MotionEvent, e2: MotionEvent, vx: Float, vy: Float): Boolean {
        (
            (), 0,
            (), 0,
            (-width).toInt(), (width * scaleFactor).toInt(),
            0, 0
        )
        postInvalidateOnAnimation()
        return true
    }
    override fun computeScroll() {
        if (()) {
            offsetX = ()
            invalidate()
        }
    }
}
 
// ---------------- document:  ----------------package 
 
import 
import 
import 
import 
import 
import 
import 
import 
 
/**
  * MainActivity: Sample Gantt Chart Display
  */
class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    private val vm: GanttViewModel by viewModels()
 
    override fun onCreate(savedInstanceState: Bundle?) {
        (savedInstanceState)
        binding = (layoutInflater)
        setContentView()
 
        // List of task names on the left        val nameAdapter = TaskNameAdapter()
         {
            layoutManager = LinearLayoutManager(this@MainActivity)
            adapter = nameAdapter
        }
 
        // Observe task data        (this) { list ->
            (list)
            (list)
        }
 
        // Added sample tasks         {
            val now = ()
            val task = Task(
                name = "Task${now%100}",
                startTime = now,
                endTime = now + 3600_000 * (1 + (now%5).toInt()),
                color = (((now/1000)%255).toInt(),120,150)
            )
            (task)
        }
    }
}
 
// ---------------- document: activity_main.xml (ViewBinding) ----------------<?xml version="1.0" encoding="utf-8"?>
<layout  xmlns:andro
         xmlns:app="/apk/res-auto">
  <data/>
  <
      android:layout_width="match_parent" android:layout_height="match_parent">
 
    <
        android:
        android:layout_width="120dp" android:layout_height="0dp"
        app:layout_constraintTop_toTopOf="parent" app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"/>
 
    <HorizontalScrollView
        android:
        android:layout_width="0dp" android:layout_height="0dp"
        android:scrollbars="none"
        app:layout_constraintTop_toTopOf="parent" app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toEndOf="@id/rvTasks" app:layout_constraintEnd_toEndOf="parent">
 
      <
          android:
          android:layout_width="2000dp" android:layout_height="match_parent"/>
    </HorizontalScrollView>
 
    <
        android:
        android:layout_width="wrap_content" android:layout_height="wrap_content"
        app:srcCompat="@android:drawable/ic_input_add"
        app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent"
        android:layout_margin="16dp"/>
  </>
</layout>