Introducing the ExifInterface Support Library

<p>With the release of the <a<br />href="https://developer.android.com/topic/libraries/support-library/revisions.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#rev25-1-0">25.1.0</a> Support Library, there's a new entry in the family: the ExifInterface Support Library. With significant improvements introduced in Android 7.1 to the framework's <code><a<br />href="https://developer.android.com/reference/android/media/ExifInterface.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog">ExifInterface</a></code>, it only made sense to make those available to all API 9+ devices via the Support Library's <code><a href="https://developer.android.com/reference/android/support/media/ExifInterface.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog">ExifInterface</a></code>. <p>The basics are still the same: the ability to read and write <a<br />href="https://en.wikipedia.org/wiki/Exif?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog">Exif</a> tags embedded within image files: now with 140 different attributes (almost 100 of them new to Android 7.1/this Support Library!) including information about the camera itself, the camera settings, orientation, and GPS coordinates. </p><h4>Camera Apps: Writing Exif Attributes</h4><p>For Camera apps, the writing is probably the most important - writing attributes is still limited to JPEG image files. Now, normally you wouldn't need to use this during the actual camera capturing itself - you'd instead be calling the Camera2 API <code><a<br />href="https://developer.android.com/reference/android/hardware/camera2/CaptureRequest.Builder.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#set(android.hardware.camera2.CaptureRequest.Key%3CT%3D,%20T)">CaptureRequest.Builder.set()</a></code> with <code><a<br />href="https://developer.android.com/reference/android/hardware/camera2/CaptureRequest.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#JPEG_ORIENTATION">JPEG_ORIENTATION</a></code>, <code><a<br />href="https://developer.android.com/reference/android/hardware/camera2/CaptureRequest.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#JPEG_GPS_LOCATION">JPEG_GPS_LOCATION</a></code> or the equivalents in the Camera1 <code><a<br />href="https://developer.android.com/reference/android/hardware/Camera.Parameters.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog">Camera.Parameters</a></code>. However, using <code>ExifInterface</code> allows you to make changes to the file after the fact (say, removing the location information on the user's request). <h4>Reading Exif Attributes</h4><p>For the rest of us though, reading those attributes is going to be our bread-and-butter; this is where we see the biggest improvements. </p><p>Firstly, you can read Exif data from JPEG and raw images (specifically, DNG, CR2, NEF, NRW, ARW, RW2, ORF, PEF, SRW and RAF files). Under the hood, this was a major restructuring, removing all native dependencies and building an extensive test suite to ensure that everything actually works. </p><p>For apps that receive images from other apps with a <code>content://</code> URI (such as those sent by apps that <a<br />href="https://developer.android.com/about/versions/nougat/android-7.0-changes.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#sharing-files">target API 24 or higher</a>), <strong><code>ExifInterface</code> now works directly off of an <code>InputStream</code></strong>; this allows you to easily extract Exif information directly out of <code>content://</code> URIs you receive without having to create a temporary file. <pre<br />class="prettyprint">Uri uri; // the URI you've received from the other app<br />InputStream in;<br />try {<br /> in = getContentResolver().openInputStream(uri);<br /> ExifInterface exifInterface = new ExifInterface(in);<br /> // Now you can extract any Exif tag you want<br /> // Assuming the image is a JPEG or supported raw format<br />} catch (IOException e) {<br /> // Handle any errors<br />} finally {<br /> if (in != null) {<br /> try {<br /> in.close();<br /> } catch (IOException ignored) {}<br /> }<br />}<br /></pre><p><strong>Note</strong>: <code>ExifInterface</code> will not work with remote <code>InputStream</code>s, such as those returned from a <code><a<br />href="https://developer.android.com/reference/java/net/HttpURLConnection.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog">HttpURLConnection</a></code>. It is strongly recommended to only use them with <code>content://</code> or <code>file://</code> URIs. <p>For most attributes, you'd simply use the <code><a<br />href="https://developer.android.com/reference/android/support/media/ExifInterface.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#getAttributeInt(java.lang.String,%20int)">getAttributeInt()</a></code>, <code><a<br />href="https://developer.android.com/reference/android/support/media/ExifInterface.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#getAttributeDouble(java.lang.String,%20double)">getAttributeDouble()</a></code>, or <code><a<br />href="https://developer.android.com/reference/android/support/media/ExifInterface.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#getAttribute(java.lang.String)">getAttribute()</a></code> (for Strings) methods as appropriate. <p>One of the most important attributes when it comes to displaying images is the image orientation, stored in the aptly-named <code><a<br />href="https://developer.android.com/reference/android/support/media/ExifInterface.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#TAG_ORIENTATION">TAG_ORIENTATION</a></code>, which returns one of the <code>ORIENTATION_</code> constants. To convert this to a rotation angle, you can post-process the value. <pre<br />class="prettyprint">int rotation = 0;<br />int orientation = exifInterface.getAttributeInt(<br /> ExifInterface.TAG_ORIENTATION,<br /> ExifInterface.ORIENTATION_NORMAL);<br />switch (orientation) {<br /> case ExifInterface.ORIENTATION_ROTATE_90:<br /> rotation = 90;<br /> break;<br /> case ExifInterface.ORIENTATION_ROTATE_180:<br /> rotation = 180;<br /> break;<br /> case ExifInterface.ORIENTATION_ROTATE_270:<br /> rotation = 270;<br /> break;<br />}<br /></pre><p>There are some helper methods to extract values from specific Exif tags. For location data, the <code><a<br />href="https://developer.android.com/reference/android/support/media/ExifInterface.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#getLatLong(float[])">getLatLong()</a></code> method gives you the latitude and longitude as floats and <code><a<br />href="https://developer.android.com/reference/android/support/media/ExifInterface.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#getAltitude(double)">getAltitude()</a></code> will give you the altitude in meters. Some images also embed a small thumbnail. You can check for its existence with <code><a<br />href="https://developer.android.com/reference/android/support/media/ExifInterface.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#hasThumbnail()">hasThumbnail()</a></code> and then extract the <code>byte[]</code> representation of the thumbnail with <code><a<br />href="https://developer.android.com/reference/android/support/media/ExifInterface.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#getThumbnail()">getThumbnail()</a></code> - perfect to pass to <code><a<br />href="https://developer.android.com/reference/android/graphics/BitmapFactory.html?utm_campaign=android_launch_exifsupportlibrary_122116&utm_source=anddev&utm_medium=blog#decodeByteArray(byte[],%20int,%20int)">BitmapFactory.decodeByteArray()</a></code>. <h4>Working with Exif: Everything is optional</h4><p>One thing that is important to understand with Exif data is that there are no required tags: each and every tag is optional - some services even specifically strip Exif data. Therefore throughout your code, you should always handle cases where there is no Exif data, either due to no data for a specific attribute or an image format that doesn't support Exif data at all (say, the ubiquitous PNGs or WebP images). </p><p>Add the ExifInterface Support Library to your project with the following dependency: </p><pre<br />class="prettyprint">compile "com.android.support:exifinterface:25.1.0"</pre><p>But when an Exif attribute is exactly what you need to prevent a mis-rotated image in your app, the ExifInterface Support Library is just what you need to #BuildBetterApps </p>

Diposting oleh Mr Xiulung