package com.vogella.android.multitouch;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PointF;
import android.util.AttributeSet;
import android.util.SparseArray;
import android.view.MotionEvent;
import android.view.View;

public class MultitouchView extends View {

    private static final int SIZE = 60;

    private SparseArray<PointF> mActivePointers;
    private Paint mPaint;
    private int[] colors = { Color.BLUE, Color.GREEN, Color.MAGENTA,
            Color.BLACK, Color.CYAN, Color.GRAY, Color.RED, Color.DKGRAY,
            Color.LTGRAY, Color.YELLOW };

    private Paint textPaint;


    public MultitouchView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView();
    }

    private void initView() {
        mActivePointers = new SparseArray<PointF>();
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        // set painter color to a color you like
        mPaint.setColor(Color.BLUE);
        mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
        textPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        textPaint.setTextSize(20);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        // get pointer index from the event object
        int pointerIndex = event.getActionIndex();

        // get pointer ID
        int pointerId = event.getPointerId(pointerIndex);

        // get masked (not specific to a pointer) action
        int maskedAction = event.getActionMasked();

        switch (maskedAction) {

        case MotionEvent.ACTION_DOWN:
        case MotionEvent.ACTION_POINTER_DOWN: {
            // We have a new pointer. Lets add it to the list of pointers

            PointF f = new PointF();
            f.x = event.getX(pointerIndex);
            f.y = event.getY(pointerIndex);
            mActivePointers.put(pointerId, f);
            break;
        }
        case MotionEvent.ACTION_MOVE: { // a pointer was moved
            for (int size = event.getPointerCount(), i = 0; i < size; i++) {
                PointF point = mActivePointers.get(event.getPointerId(i));
                if (point != null) {
                    point.x = event.getX(i);
                    point.y = event.getY(i);
                }
            }
            break;
        }
        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_POINTER_UP:
        case MotionEvent.ACTION_CANCEL: {
            mActivePointers.remove(pointerId);
            break;
        }
        }
        invalidate();

        return true;
    }

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

        // draw all pointers
        for (int size = mActivePointers.size(), i = 0; i < size; i++) {
            PointF point = mActivePointers.valueAt(i);
            if (point != null)
                mPaint.setColor(colors[i % 9]);
            canvas.drawCircle(point.x, point.y, SIZE, mPaint);
        }
        canvas.drawText("Total pointers: " + mActivePointers.size(), 10, 40 , textPaint);
    }

}

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

    <com.vogella.android.multitouch.MultitouchView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />

</RelativeLayout>

package com.vogella.android.multitouch;

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

public class MainActivity extends Activity {

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

}

package de.vogella.android.touch.scaledetector;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.drawable.Drawable;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;

public class ImageViewWithZoom extends View {
    private Drawable image;
    private float scaleFactor = 1.0f;
    private ScaleGestureDetector scaleGestureDetector;

    public ImageViewWithZoom(Context context) {
        super(context);
        image = context.getResources().getDrawable(R.drawable.icon);
        setFocusable(true);
        image.setBounds(0, 0, image.getIntrinsicWidth(),
                image.getIntrinsicHeight());
        scaleGestureDetector = new ScaleGestureDetector(context,
                new ScaleListener());
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        // Set the image bounderies
        canvas.save();
        canvas.scale(scaleFactor, scaleFactor);
        image.draw(canvas);
        canvas.restore();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        scaleGestureDetector.onTouchEvent(event);
        invalidate();
        return true;
    }

    private class ScaleListener extends
            ScaleGestureDetector.SimpleOnScaleGestureListener {
        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            scaleFactor *= detector.getScaleFactor();

            // don't let the object get too small or too large.
            scaleFactor = Math.max(0.1f, Math.min(scaleFactor, 5.0f));

            invalidate();
            return true;
        }
    }
}

package de.vogella.android.touch.scaledetector;

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

public class ScaleDetectorTestActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new ImageViewWithZoom(this));
    }
}