How to create a floating window like Clipboard Pro App?

You can create a floating view using WindowManager by granting Draw Overlays permission only for APIs above M. (For APIs below 23, this permission is always granted)

I have developed a sample code that you can use it simply. (Available on GitHub: https://github.com/aminography/FloatingWindowApp)

SimpleFloatingWindow.kt:

import android.content.Context
import android.content.Context.WINDOW_SERVICE
import android.graphics.PixelFormat
import android.os.Build
import android.view.*
import kotlinx.android.synthetic.main.layout_floating_window.view.*
import kotlin.math.abs


/**
 * @author aminography
 */
class SimpleFloatingWindow constructor(private val context: Context) {

    private var windowManager: WindowManager? = null
        get() {
            if (field == null) field = (context.getSystemService(WINDOW_SERVICE) as WindowManager)
            return field
        }

    private var floatView: View =
        LayoutInflater.from(context).inflate(R.layout.layout_floating_window, null)

    private lateinit var layoutParams: WindowManager.LayoutParams

    private var lastX: Int = 0
    private var lastY: Int = 0
    private var firstX: Int = 0
    private var firstY: Int = 0

    private var isShowing = false
    private var touchConsumedByMove = false

    private val onTouchListener = View.OnTouchListener { view, event ->
        val totalDeltaX = lastX - firstX
        val totalDeltaY = lastY - firstY

        when (event.actionMasked) {
            MotionEvent.ACTION_DOWN -> {
                lastX = event.rawX.toInt()
                lastY = event.rawY.toInt()
                firstX = lastX
                firstY = lastY
            }
            MotionEvent.ACTION_UP -> {
                view.performClick()
            }
            MotionEvent.ACTION_MOVE -> {
                val deltaX = event.rawX.toInt() - lastX
                val deltaY = event.rawY.toInt() - lastY
                lastX = event.rawX.toInt()
                lastY = event.rawY.toInt()
                if (abs(totalDeltaX) >= 5 || abs(totalDeltaY) >= 5) {
                    if (event.pointerCount == 1) {
                        layoutParams.x += deltaX
                        layoutParams.y += deltaY
                        touchConsumedByMove = true
                        windowManager?.apply {
                            updateViewLayout(floatView, layoutParams)
                        }
                    } else {
                        touchConsumedByMove = false
                    }
                } else {
                    touchConsumedByMove = false
                }
            }
            else -> {
            }
        }
        touchConsumedByMove
    }

    init {
        with(floatView) {
            closeImageButton.setOnClickListener { dismiss() }
            textView.text = "I'm a float view!"
        }

        floatView.setOnTouchListener(onTouchListener)

        layoutParams = WindowManager.LayoutParams().apply {
            format = PixelFormat.TRANSLUCENT
            flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
            @Suppress("DEPRECATION")
            type = when {
                Build.VERSION.SDK_INT >= Build.VERSION_CODES.O ->
                    WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY
                else -> WindowManager.LayoutParams.TYPE_TOAST
            }

            gravity = Gravity.CENTER
            width = WindowManager.LayoutParams.WRAP_CONTENT
            height = WindowManager.LayoutParams.WRAP_CONTENT
        }
    }

    fun show() {
        if (context.canDrawOverlays) {
            dismiss()
            isShowing = true
            windowManager?.addView(floatView, layoutParams)
        }
    }

    fun dismiss() {
        if (isShowing) {
            windowManager?.removeView(floatView)
            isShowing = false
        }
    }
}

layout_floating_window.xml:

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <androidx.appcompat.widget.AppCompatTextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#ff4444"
        android:padding="32dp"
        android:text="text"
        android:textColor="#ffffff"
        android:textSize="24sp" />

    <androidx.appcompat.widget.AppCompatImageButton
        android:id="@+id/closeImageButton"
        style="@style/Base.Widget.AppCompat.Button.Borderless"
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:layout_gravity="top|right"
        android:src="@drawable/ic_close_white_24dp" />

</FrameLayout>

MainActivity.kt:

import android.content.Intent
import android.net.Uri
import android.os.Build
import android.os.Bundle
import android.provider.Settings
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*

/**
 * @author aminography
 */
class MainActivity : AppCompatActivity() {

    private lateinit var simpleFloatingWindow: SimpleFloatingWindow

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

        simpleFloatingWindow = SimpleFloatingWindow(applicationContext)

        button.setOnClickListener {
            if (canDrawOverlays) {
                simpleFloatingWindow.show()
            } else {
                startManageDrawOverlaysPermission()
            }
        }
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        when (requestCode) {
            REQUEST_CODE_DRAW_OVERLAY_PERMISSION -> {
                if (canDrawOverlays) {
                    simpleFloatingWindow.show()
                } else {
                    showToast("Permission is not granted!")
                }
            }
        }
    }

    private fun startManageDrawOverlaysPermission() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            Intent(
                Settings.ACTION_MANAGE_OVERLAY_PERMISSION,
                Uri.parse("package:${applicationContext.packageName}")
            ).let {
                startActivityForResult(it, REQUEST_CODE_DRAW_OVERLAY_PERMISSION)
            }
        }
    }

    companion object {
        private const val REQUEST_CODE_DRAW_OVERLAY_PERMISSION = 5
    }
}

Extensions.kt:

import android.content.Context
import android.os.Build
import android.provider.Settings
import android.widget.Toast

/**
 * @author aminography
 */

private var toast: Toast? = null

fun Context.showToast(message: CharSequence?) {
    message?.let {
        toast?.cancel()
        toast = Toast.makeText(this, message, Toast.LENGTH_SHORT).apply { show() }
    }
}

val Context.canDrawOverlays: Boolean
    get() = Build.VERSION.SDK_INT < Build.VERSION_CODES.M || Settings.canDrawOverlays(this)

Visual Result: