User touch input

1) Single-touch

/*
	Simple code to get the user single-touch input
	and draw a rectangle where the screen is touched.

	It is assumed that you already followed the
	content of the page on 'Simple draw pixels'.

	To build and run the android app, first
	follow the steps to 'Get everything ready'.

	Then inside the project folder and inside src/com/example/,
	replace the entire code in MainActivity.java file with this code.

	Use at your own risk!
*/

package com.example.myfirstapp;

import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.view.MotionEvent;
import android.view.View;


public class MainActivity extends Activity
{
	/** Called when the activity is first created. */
	@Override
	public void onCreate (Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		//setContentView(R.layout.main);    // this is the default view but which is replaced.
		setContentView(new MyView(this));   // the activity will have only one view 'MyView'.
	}

	private class MyView extends View       // custom view so to override onDraw()
	{
		int width, height;
		int[] pixels_colours;
		boolean firstTime = true;

		public MyView(Context context)      // class constructor that must be present
		{ super(context); }


		@Override                           // here is the purpose of extending the View class
		protected void onDraw(Canvas canvas)
		{
			if(firstTime)
			{
				firstTime = false;

				// Get width and height of the View. These will be for the
				// full area taken by the activity since it has only one view.
				width = getWidth();
				height = getHeight();

				// array to store the colours for all the pixels
				pixels_colours = new int[height*width];

				for(int y=0; y<height; y++)
					for(int x=0; x<width; x++)
						pixels_colours[y*width+x] = (x + y<<16); // any colour
			}

			// draw to screen of device
			canvas.drawBitmap (pixels_colours, 0, width, 0, 0, width, height, false, null);
		}

		void myDrawRectangle (int x, int y, int colour)
		{
			for(int i=x-4; i<x+4; i++)
				for(int j=y-4; j<y+4; j++)
					if(i>=0 && i<width && j>=0 && j<height)
						pixels_colours[j*width+i] = colour;
		}

		@Override
		public boolean onTouchEvent (MotionEvent event)
		{
			int x = (int)event.getX();      // get the (x,y) position
			int y = (int)event.getY();      // relative to the view

			switch (event.getAction())
			{
				case MotionEvent.ACTION_DOWN:           // on a press,
					myDrawRectangle(x, y, 0x000000FF);  // draw a blue rectangle
					break;

				case MotionEvent.ACTION_MOVE:           // on a move,
					myDrawRectangle(x, y, 0x0000FF00);  // draw a green rectangle
					break;

				case MotionEvent.ACTION_UP:             // on a release,
					myDrawRectangle(x, y, 0x00FF0000);  // draw a red rectangle
					break;

				case MotionEvent.ACTION_CANCEL:         // on a cancellation,
					myDrawRectangle(x, y, 0x00000000);  // draw a black rectangle
					break;

				default: return false;  // may not be needed
			}

			invalidate();   // schedule a refresh of the View

			return true;
			// more at http://developer.android.com/reference/android/view/MotionEvent.html
		}
	}
}

2) Multi-touch

        /* Read the code, let it speak for itself! */
		@Override
		public boolean onTouchEvent (MotionEvent event)
		{
			int x, y, index, count;

			switch (event.getAction())
			{
				case MotionEvent.ACTION_DOWN:
				case MotionEvent.ACTION_POINTER_DOWN:
				case MotionEvent.ACTION_UP:
				case MotionEvent.ACTION_POINTER_UP:
				case MotionEvent.ACTION_MOVE:

					count = event.getPointerCount();
					for(index=0; index < count; index++)
					{
						x = (int)event.getX(index);
						y = (int)event.getY(index);

						// draw the rectangle with a colour
						// that depends on the pointer index
						myDrawRectangle(x, y, 0xFF<<(8*index));
					}
					break;

				case MotionEvent.ACTION_CANCEL:
					return false;

				default: return false;  // may not be needed
			}

			invalidate();   // schedule a refresh of the View

			return true;
		}