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copied!<p>It depends on the version of Android you wish to target.</p> <ul> <li>2.2 or newer - use the built-in ScaleGestureDetector. The javadoc is very helpful, but see the example below.</li> <li>2.0-2.2 - ScaleGestureDetector isn't built-in, so <a href="http://www.google.com/codesearch/p?hl=en#uX1GffpyOZk/core/java/android/view/ScaleGestureDetector.java" rel="nofollow">copy the version from Android</a> and compile it into your application.</li> <li>Pre-2.0 - Mutitouch wasn't supported before 2.0, so you need to <a href="http://www.google.com/codesearch/p?hl=en#uX1GffpyOZk/core/java/android/view/ScaleGestureDetector.java" rel="nofollow">copy ScaleGestureDetector.java from Android</a> and do a little more work to not use any multitouch APIs on unsupported devices:</li> </ul> <p>To avoid using multitouch APIs on pre-2.0 devices, you need to create an interface for the ScaleGestureDetector (Eclipse can do this via the Refactor menu), and a dummy implementation which 1.x devices will use. We'll call our interface <code>ScaleGestureDetectorInterface</code> and our dummy implementation <code>FakeScaleGestureDetector</code>.</p> <p>Here is a sample supporting pre-2.0 devices:</p> <pre><code>// If you don't care about pre-2.0 devices, just make this a // ScaleGestureDetector and skip the API check in the constructor. private final ScaleGestureDetectorInterface mScaleDetector; public MyView { if (Build.VERSION.SDK_INT < Build.VERSION_CODES.ECLAIR) { // Use the fake version which won't call any multitouch APIs mScaleDetector = new FakeScaleGestureDetector(); } else { // We are using SDK 2.0+, use the real implementation. mScaleDetector = new ScaleGestureDetector(context, new MyScaleListener()); } } @Override public boolean onTouchEvent(MotionEvent event) { // On pre-2.0, the implementation does nothing. return mScaleDetector.onTouchEvent(event); } private class MyScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener { @Override public boolean onScale(ScaleGestureInterface detector) { float scaleFactor = detector.getScaleFactor(); // If you were using a matrix to zoom an ImageView, you would do // something like this: mMatrix.postScale(scaleFactor, scaleFactor, detector.getFocusX(), detector.getFocusY()); return true; } } </code></pre>

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