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copied!<p>A first order approximation would be to sum up the local length of every tiny piece of movement detected :</p> <p>On <code>ACTION_DOWN</code></p> <pre><code>total = 0; xPrec = ev.getX(); yPrec = ev.getY(); </code></pre> <p>On <code>ACTION_MOVE</code></p> <pre><code>final float dx = ev.getX() - xPrec; final float dy = ev.getY() - yPrec; final float dl = sqrt(dx * dx + dy * dy); total += dl; xPrec = ev.getX(); yPrec = ev.getY(); </code></pre> <p>On <code>ACTION_UP</code> you can do whatever you want with <code>total</code> which contains the total approximated length of your path.</p> <p>If you read the official documentation about <code>MotionEvent</code> <a href="http://developer.android.com/reference/android/view/MotionEvent.html" rel="nofollow">http://developer.android.com/reference/android/view/MotionEvent.html</a> you will see a section entitled <strong>Batching</strong> which explains that one given motion event can batch together multiple movement samples. For the best first order approximation you need to consume all those samples using <code>getHistorySize</code>, <code>getHistoricalX</code>, <code>getHistoricalY</code>. Don't forget to process the most recent sample which stands in <code>getX</code> and <code>getY</code>.</p> <p>If you need a better approximation I suggest you to read about the problem of curve fitting <a href="http://en.wikipedia.org/wiki/Curve_fitting" rel="nofollow">http://en.wikipedia.org/wiki/Curve_fitting</a>, but as the frequency of touch events is quite fast you may not need to do so and get satisfied with a first order approximation.</p>

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