android kotlin - Drag and drop easy example

MainActivity.kt


package com.example.jetpack

import android.content.ClipData
import android.content.ClipDescription
import android.graphics.Canvas
import android.graphics.Color
import android.graphics.Point
import android.graphics.drawable.ColorDrawable
import android.os.Build
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.DragEvent
import android.view.View
import android.widget.TextView
import kotlinx.android.synthetic.main.activity_main.*
import java.util.*

class MainActivity : AppCompatActivity() {

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

        val randomNumber = Random().nextInt(100)
        textView.text = "$randomNumber"
        textView.tag = textView.text

        textView.setOnClickListener {v->
            val randomNumber = Random().nextInt(100)
            (v as TextView).text = "$randomNumber"
            (v as TextView).tag = (v as TextView).text
        }

        textView.setOnLongClickListener { v:View ->
            val item = ClipData.Item(v.tag as? CharSequence)

            val dragData = ClipData(
                v.tag as CharSequence,
                arrayOf(ClipDescription.MIMETYPE_TEXT_PLAIN),
                item
            )

            val myShadow = MyDragShadowBuilder(v)

            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
                v.startDragAndDrop(dragData,myShadow,null,0)
            }else{
                v.startDrag(dragData,myShadow,null,0)
            }
        }

        textView2.setOnDragListener(dragListen)
    }


    private class MyDragShadowBuilder(v: View) : View.DragShadowBuilder(v) {
        private val shadow = ColorDrawable(Color.LTGRAY)

        override fun onProvideShadowMetrics(size: Point, touch: Point) {
            val width: Int = (view.width / 1.2F).toInt()
            val height: Int = (view.height / 1.2F).toInt()
            //val width: Int = view.width / 2
            //val height: Int = view.height / 2

            shadow.setBounds(0, 0, width, height)
            size.set(width, height)
            touch.set(width / 2, height / 2)
        }
        override fun onDrawShadow(canvas: Canvas) {
            shadow.draw(canvas)
        }
    }


    // Creates a new drag event listener
    private val dragListen = View.OnDragListener { v, event ->
        val receiverView:TextView = v as TextView

        when (event.action) {
            DragEvent.ACTION_DRAG_STARTED -> {
                if (event.clipDescription.hasMimeType(ClipDescription.MIMETYPE_TEXT_PLAIN)) {
                    receiverView.setBackgroundColor(Color.CYAN)
                    receiverView.text = "Hold and drag here."
                    v.invalidate()
                    true
                } else {
                    false
                }
            }

            DragEvent.ACTION_DRAG_ENTERED -> {
                receiverView.setBackgroundColor(Color.GREEN)
                receiverView.text = "Good, put here."
                v.invalidate()
                true
            }

            DragEvent.ACTION_DRAG_LOCATION ->
                true

            DragEvent.ACTION_DRAG_EXITED -> {
                receiverView.setBackgroundColor(Color.YELLOW)
                receiverView.text = "Oh! you exited."
                v.invalidate()
                true
            }

            DragEvent.ACTION_DROP -> {
                val item: ClipData.Item = event.clipData.getItemAt(0)
                val dragData = item.text
                receiverView.text = "You dropped : $dragData"
                v.invalidate()
                true
            }

            DragEvent.ACTION_DRAG_ENDED -> {
                receiverView.setBackgroundColor(Color.WHITE)
                v.invalidate()


                when(event.result) {
                    true ->
                        // drop was handled
                        receiverView.setBackgroundColor(Color.WHITE)
                    else ->{
                        // drop didn't work
                        receiverView.text = "Drop failed."
                        receiverView.setBackgroundColor(Color.RED)
                        }
                }

                // returns true; the value is ignored.
                true
            }

            else -> {
                // An unknown action type was received.
                false
            }
        }
    }
}

activity_main.xml


<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="32dp"
        android:background="#77B5FE"
        android:padding="30dp"
        tools:text="Drag Me"
        android:textStyle="bold"
        android:textAppearance="@style/TextAppearance.AppCompat.Medium"
        android:textColor="#0072BB"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>
    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#FD3F92"
        android:padding="15dp"
        android:text="Drop Here"
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

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