Usando Canvas de Android

En esta entrada les muestro el código para mostrar bolitas y que reaccionen al evento onTouch:

	package com.cecy.practica3;
	import android.app.Activity;
	import android.content.Context;
	import android.graphics.Canvas;
	import android.graphics.Paint;
	import android.os.Bundle;
	import android.view.MotionEvent;
	import android.view.View;
	import android.view.View.OnTouchListener;
	import android.widget.LinearLayout;
	public class Practica3Activity extends Activity implements OnTouchListener{
	/** Called when the activity is first created. */
	private float corX, corY;
	private Lienzo fondo;
	private int pintados[][] = new int[10][10];
	@Override
	public void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.main);
	LinearLayout linearLayout = (LinearLayout)findViewById(R.id.linearLayout1);
	corX = 0;
	corY = 0;
	for(int j=0;j<10;j++){
	for(int i=0; i<10; i++){
	pintados[i][j] = 0;
	}
	}
	fondo = new Lienzo(this);
	fondo.setOnTouchListener(this);
	linearLayout.addView(fondo);
	}
	public boolean onTouch(View v, MotionEvent event) {
	corX = (float)event.getX();
	corY = (float)event.getY();
	fondo.invalidate();
	return true;
	}
	class Lienzo extends View {
	public Lienzo(Context context) {
	super(context);
	}
	protected void onDraw(Canvas canvas) {
	float ancho=canvas.getWidth();
	float alto=canvas.getHeight();
	float tamX = ancho/10;
	float mitX = tamX/2;
	float radio = 6;
	float inicialX = mitX;
	float inicialY = mitX;
	Paint pincel1=new Paint();
	pincel1.setARGB(255,124,205,124);
	for(int j=0;j<10;j++){
	for(int i=0; i<10; i++){
	if(pintados[i][j] == 1 && corX < (inicialX+radio) && corX > (inicialX-radio) && corY > (inicialY-radio) && corY < (inicialY +radio)){
	pincel1.setARGB(255,124,205,124);
	canvas.drawCircle(inicialX, inicialY, radio, pincel1);
	pintados[i][j] = 0;
	}
	else if(corX < (inicialX+radio) && corX > (inicialX-radio) && corY > (inicialY-radio) && corY < (inicialY +radio) && pintados[i][j] != 1){
	pincel1.setARGB(255,255,0,0);
	canvas.drawCircle(inicialX, inicialY, radio, pincel1);
	pintados[i][j] = 1;
	}
	else if(pintados[i][j] == 1){
	pincel1.setARGB(255,255,0,0);
	canvas.drawCircle(inicialX, inicialY, radio, pincel1);
	pintados[i][j] = 1;
	}
	else{
	pincel1.setARGB(255,124,205,124);
	canvas.drawCircle(inicialX, inicialY, radio, pincel1);
	pintados[i][j] = 0;
	}
	inicialX = inicialX + tamX;
	}
	inicialY = inicialY + tamX;
	inicialX = mitX;
	}
	//canvas.drawCircle(corX, corY, 15, pincel1);
	}
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

Y con esto obtengo lo siguiente: