Mobile App Dev 2022W: Tutorial 8

Documentation

• Android: Drawables from xml
• Android: Drag an object
• Android: getLocationOnScreen

Code

app/src/main/java/carleton/comp1601/dragdemo3/MainActivity.kt

package carleton.comp1601.dragdemo3

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.MotionEvent
import android.view.View
import kotlin.math.abs
import android.widget.TextView

class MainActivity : AppCompatActivity() {
    private lateinit var redCircle: View
    private lateinit var blueSquare: View
    private lateinit var status: TextView

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        redCircle = findViewById(R.id.redCircle)
        redCircle.setOnTouchListener(trackCircle)
        blueSquare = findViewById(R.id.blueSquare)
        status = findViewById(R.id.status)
    }

    val trackCircle = object: View.OnTouchListener {
        override fun onTouch(v: View?, event: MotionEvent?): Boolean {
            if (event == null || v == null) {
                return false
            }

            val action = event.getAction()
            val x = event.rawX
            val y = event.rawY

            var circleScreenLoc = IntArray(2)
            redCircle.getLocationOnScreen(circleScreenLoc)
            val circleOffsetX = circleScreenLoc[0] - redCircle.x
            val circleOffsetY = circleScreenLoc[1] - redCircle.y

            if (action == MotionEvent.ACTION_MOVE) {
                redCircle.x = x - (redCircle.width/2 + circleOffsetX)
                redCircle.y = y - (redCircle.height/2 + circleOffsetY)
            }

            var squareScreenLoc = IntArray(2)
            blueSquare.getLocationOnScreen(squareScreenLoc)
            val squareCenterX = squareScreenLoc[0] + blueSquare.width/2
            val squareCenterY = squareScreenLoc[1] + blueSquare.height/2

            if ((abs(x - squareCenterX) < 50) and
                (abs(y - squareCenterY) < 50)) {
                status.setText("Success!")
            } else {
                status.setText("Drag the circle into the box")
            }

            return true
        }
    }
}

app/src/main/res/layout/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">

    <ImageView
        android:id="@+id/blueSquare"
        android:layout_width="150dp"
        android:layout_height="150dp"
        android:layout_marginTop="20dp"
        android:layout_marginStart="20dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/square" />

    <ImageView
        android:id="@+id/redCircle"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:layout_marginBottom="20dp"
        android:layout_marginEnd="20dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:srcCompat="@drawable/circle" />

    <TextView
        android:id="@+id/status"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Drag the circle into the box"
        android:textAlignment="center"
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

app/src/main/res/drawable/circle.xml

<?xml version="1.0" encoding="utf-8"?>
<shape android:shape="oval" xmlns:android="http://schemas.android.com/apk/res/android">
    <solid android:color="#ff0000"/>
</shape>

app/src/main/res/drawable/square.xml

<?xml version="1.0" encoding="utf-8"?>
<shape android:shape="rectangle" xmlns:android="http://schemas.android.com/apk/res/android">
    <stroke android:width="10dp" android:color="#0000ff" />
</shape>