T
- The type of the resource being transformed.public interface Transformation<T> extends Key
Key.equals(Object)
and Key.hashCode()
} to identify the transformation in the memory
cache and Key.updateDiskCacheKey(java.security.MessageDigest)
} to identify the
transformation in disk caches.
Using the fully qualified class name as a static final String
(not
Class.getName()
to avoid proguard obfuscation) is an easy way to implement
Key.updateDiskCacheKey(java.security.MessageDigest)
} correctly. If additional arguments are
required they can be passed in to the constructor of the Transformation
and then used to
update the MessageDigest
passed in to
Key.updateDiskCacheKey(MessageDigest)
. If arguments are primitive types, they can typically
easily be serialized using ByteBuffer
. String
types can be serialized
with String.getBytes(Charset)
using the constant Key.CHARSET
.
Implementations must implement Key.equals(Object)
and Key.hashCode()
for
memory caching to work correctly.
CHARSET, STRING_CHARSET_NAME
Modifier and Type | Method and Description |
---|---|
Resource<T> |
transform(Context context,
Resource<T> resource,
int outWidth,
int outHeight)
Transforms the given resource and returns the transformed resource.
|
equals, hashCode, updateDiskCacheKey
@NonNull Resource<T> transform(@NonNull Context context, @NonNull Resource<T> resource, int outWidth, int outHeight)
If the original resource object is not returned, the original resource will be recycled and it's internal resources may be reused. This means it is not safe to rely on the original resource or any internal state of the original resource in any new resource that is created. Usually this shouldn't occur, but if absolutely necessary either the original resource object can be returned with modified internal state, or the data in the original resource can be copied into the transformed resource.
If a Transformation is updated, Key.equals(Object)
, Key.hashCode()
, and
Key.updateDiskCacheKey(java.security.MessageDigest)
should all change. If you're using a
simple String key an easy way to do this is to append a version number to your key. Failing to
do so will mean users may see images loaded from cache that had the old version of the
Transformation applied. Changing the return values of those methods will ensure that the cache
key has changed and therefore that any cached resources will be re-generated using the updated
Transformation.
During development you may need to either using DiskCacheStrategy.NONE
or make sure Key.updateDiskCacheKey(java.security.MessageDigest)
changes each time you make a change to the
Transformation. Otherwise the resource you request may be loaded from disk cache and your
Transformation may not be called.
context
- The Application contextresource
- The resource to transform.outWidth
- The width of the view or target the resource will be displayed in, or Target.SIZE_ORIGINAL
to indicate the
original resource width.outHeight
- The height of the view or target the resource will be displayed in, or Target.SIZE_ORIGINAL
to indicate the
original resource height.