teaching machines

CS 145 Lecture 36 – Android

Agenda

  • what ?s
  • event-driven programming
  • bubble wrap popper
  • Android’s view¬†system
  • callbacks
  • resource management
  • touch events

Code

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                xmlns:tools="http://schemas.android.com/tools"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                tools:context=".MainActivity">

  <view
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    class="org.twodee.popper2.PopperView"
    android:id="@+id/view"
    android:layout_centerVertical="true"
    android:layout_centerHorizontal="true"/>
</RelativeLayout>

MainActivity.java

package org.twodee.popper2;

import android.app.Activity;
import android.os.Bundle;


public class MainActivity extends Activity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
  }

}

PopperView.java

package org.twodee.popper2;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

import java.util.Random;

public class PopperView extends View {
  private Bitmap[] images;
  private boolean[][] isPopped;

  public PopperView(Context context,
                    AttributeSet attrs) {
    super(context, attrs);
    images = new Bitmap[2];
    images[0] = BitmapFactory.decodeResource(getResources(), R.drawable.unpopped);
    images[1] = BitmapFactory.decodeResource(getResources(), R.drawable.popped);
  }

  @Override
  protected void onSizeChanged(int w,
                               int h,
                               int oldw,
                               int oldh) {
    int nColumns = (int) Math.ceil(w / (double) images[0].getWidth());
    int nRows = (int) Math.ceil(h / (double) images[0].getHeight());

    isPopped = new boolean[nRows][nColumns];

    super.onSizeChanged(w, h, oldw, oldh);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    for (int r = 0; r < isPopped.length; ++r) {
      for (int c = 0; c < isPopped[r].length; ++c) {
        if (isPopped[r][c]) {
          canvas.drawBitmap(images[1], c * images[0].getWidth(), r * images[0].getHeight(), null);
        } else {
          canvas.drawBitmap(images[0], c * images[0].getWidth(), r * images[0].getHeight(), null);
        }
      }
    }
  }

  private void popAt(float x, float y) {
    int r = (int) y / images[0].getHeight();
    int c = (int) x / images[0].getWidth();

    if (!isPopped[r][c]) {
      isPopped[r][c] = true;
      playSound();
      invalidate();
    }
  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    for (int i = 0; i < event.getPointerCount(); ++i) {
      popAt(event.getX(i), event.getY(i));
    }

    return true;
  }

  private void playSound() {
    final MediaPlayer player = MediaPlayer.create(getContext(), getRandomAudioID());
    player.start();
    player.setOnCompletionListener(new OnCompletionListener() {
      @Override
      public void onCompletion(MediaPlayer mp) {
        player.release();
      }
    });
  }

  private int getRandomAudioID() {
    int[] ids = {R.raw.pop1, R.raw.pop2, R.raw.pop3};
    return ids[new Random().nextInt(ids.length)];
  }
}

Haiku

on the merits of technology:
I don’t have more time
Instead, I do a lot more
Thanks, technology!

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