Android源码阅读遗留问题
ImageDecoder.java(Android 9)
File file = new File(filePath);
// FileSource
ImageDecoder.Source source = ImageDecoder.createSource(file);
Bitmap drawable = ImageDecoder.decodeBitmap(source);
FileSource被强转成了InputStreamSource：
/**
* Class for decoding images as {@link Bitmap}s or {@link Drawable}s.
*/
public final class ImageDecoder implements AutoCloseable {
/**
* Create a {@link Bitmap} from a {@code Source}.
*
* @param src representing the encoded image.
* @param listener for learning the {@link ImageInfo} and changing any
* default settings on the {@code ImageDecoder}. If not {@code null},
* this will be called on the same thread as {@code decodeBitmap}
* before that method returns.
* @return Bitmap containing the image.
* @throws IOException if {@code src} is not found, is an unsupported
* format, or cannot be decoded for any reason.
*/
@NonNull
public static Bitmap decodeBitmap(@NonNull Source src,
@Nullable OnHeaderDecodedListener listener) throws IOException {
TypedValue value = new TypedValue();
value.density = src.getDensity();
ImageDecoder decoder = src.createImageDecoder();
if (listener != null) {
listener.onHeaderDecoded(decoder, new ImageInfo(decoder), src);
}
return BitmapFactory.decodeResourceStream(src.getResources(), value,
((InputStreamSource) src).mInputStream, decoder.mOutPaddingRect, null);
}
}
而FileSource和InputStreamSource并无继承关系：
private static class FileSource extends Source {
FileSource(@NonNull File file) {
mFile = file;
}
private final File mFile;
@Override
public ImageDecoder createImageDecoder() throws IOException {
return new ImageDecoder();
}
}
/**
* For backwards compatibility, this does *not* close the InputStream.
*/
private static class InputStreamSource extends Source {
InputStreamSource(Resources res, InputStream is, int inputDensity) {
if (is == null) {
throw new IllegalArgumentException("The InputStream cannot be null");
}
mResources = res;
mInputStream = is;
mInputDensity = res != null ? inputDensity : Bitmap.DENSITY_NONE;
}
final Resources mResources;
InputStream mInputStream;
final int mInputDensity;
@Override
public Resources getResources() { return mResources; }
@Override
public int getDensity() { return mInputDensity; }
@Override
public ImageDecoder createImageDecoder() throws IOException {
return new ImageDecoder();
}
}
且Android Studio关联的源码和Googlesource网站上的源码不一致：https://android.googlesource.com/platform/frameworks/base/+/refs/heads/master/graphics/java/android/graphics/ImageDecoder.java：
/**
* <p>A class for converting encoded images (like {@code PNG}, {@code JPEG},
* {@code WEBP}, {@code GIF}, or {@code HEIF}) into {@link Drawable} or
* {@link Bitmap} objects.
*
* <p>To use it, first create a {@link Source Source} using one of the
* {@code createSource} overloads. For example, to decode from a {@link File}, call
* {@link #createSource(File)} and pass the result to {@link #decodeDrawable(Source)}
* or {@link #decodeBitmap(Source)}:
*
* <pre class="prettyprint">
* File file = new File(...);
* ImageDecoder.Source source = ImageDecoder.createSource(file);
* Drawable drawable = ImageDecoder.decodeDrawable(source);
* </pre>
*
* <p>To change the default settings, pass the {@link Source Source} and an
* {@link OnHeaderDecodedListener OnHeaderDecodedListener} to
* {@link #decodeDrawable(Source, OnHeaderDecodedListener)} or
* {@link #decodeBitmap(Source, OnHeaderDecodedListener)}. For example, to
* create a sampled image with half the width and height of the original image,
* call {@link #setTargetSampleSize setTargetSampleSize(2)} inside
* {@link OnHeaderDecodedListener#onHeaderDecoded onHeaderDecoded}:
*
* <pre class="prettyprint">
* OnHeaderDecodedListener listener = new OnHeaderDecodedListener() {
* public void onHeaderDecoded(ImageDecoder decoder, ImageInfo info, Source source) {
* decoder.setTargetSampleSize(2);
* }
* };
* Drawable drawable = ImageDecoder.decodeDrawable(source, listener);
* </pre>
*
* <p>The {@link ImageInfo ImageInfo} contains information about the encoded image, like
* its width and height, and the {@link Source Source} can be used to match to a particular
* {@link Source Source} if a single {@link OnHeaderDecodedListener OnHeaderDecodedListener}
* is used with multiple {@link Source Source} objects.
*
* <p>The {@link OnHeaderDecodedListener OnHeaderDecodedListener} can also be implemented
* as a lambda:
*
* <pre class="prettyprint">
* Drawable drawable = ImageDecoder.decodeDrawable(source, (decoder, info, src) -> {
* decoder.setTargetSampleSize(2);
* });
* </pre>
*
* <p>If the encoded image is an animated {@code GIF} or {@code WEBP},
* {@link #decodeDrawable decodeDrawable} will return an {@link AnimatedImageDrawable}. To
* start its animation, call {@link AnimatedImageDrawable#start AnimatedImageDrawable.start()}:
*
* <pre class="prettyprint">
* Drawable drawable = ImageDecoder.decodeDrawable(source);
* if (drawable instanceof AnimatedImageDrawable) {
* ((AnimatedImageDrawable) drawable).start();
* }
* </pre>
*
* <p>By default, a {@link Bitmap} created by {@link ImageDecoder} (including
* one that is inside a {@link Drawable}) will be immutable (i.e.
* {@link Bitmap#isMutable Bitmap.isMutable()} returns {@code false}), and it
* will typically have {@code Config} {@link Bitmap.Config#HARDWARE}. Although
* these properties can be changed with {@link #setMutableRequired setMutableRequired(true)}
* (which is only compatible with {@link #decodeBitmap(Source)} and
* {@link #decodeBitmap(Source, OnHeaderDecodedListener)}) and {@link #setAllocator},
* it is also possible to apply custom effects regardless of the mutability of
* the final returned object by passing a {@link PostProcessor} to
* {@link #setPostProcessor setPostProcessor}. A {@link PostProcessor} can also be a lambda:
*
* <pre class="prettyprint">
* Drawable drawable = ImageDecoder.decodeDrawable(source, (decoder, info, src) -> {
* decoder.setPostProcessor((canvas) -> {
* // This will create rounded corners.
* Path path = new Path();
* path.setFillType(Path.FillType.INVERSE_EVEN_ODD);
* int width = canvas.getWidth();
* int height = canvas.getHeight();
* path.addRoundRect(0, 0, width, height, 20, 20, Path.Direction.CW);
* Paint paint = new Paint();
* paint.setAntiAlias(true);
* paint.setColor(Color.TRANSPARENT);
* paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));
* canvas.drawPath(path, paint);
* return PixelFormat.TRANSLUCENT;
* });
* });
* </pre>
*
* <p>If the encoded image is incomplete or contains an error, or if an
* {@link Exception} occurs during decoding, a {@link DecodeException DecodeException}
* will be thrown. In some cases, the {@link ImageDecoder} may have decoded part of
* the image. In order to display the partial image, an
* {@link OnPartialImageListener OnPartialImageListener} must be passed to
* {@link #setOnPartialImageListener setOnPartialImageListener}. For example:
*
* <pre class="prettyprint">
* Drawable drawable = ImageDecoder.decodeDrawable(source, (decoder, info, src) -> {
* decoder.setOnPartialImageListener((DecodeException e) -> {
* // Returning true indicates to create a Drawable or Bitmap even
* // if the whole image could not be decoded. Any remaining lines
* // will be blank.
* return true;
* });
* });
* </pre>
*/
public final class ImageDecoder implements AutoCloseable {
/**
* Create a {@link Bitmap} from a {@code Source}.
*
* @param src representing the encoded image.
* @param listener for learning the {@link ImageInfo ImageInfo} and changing any
* default settings on the {@code ImageDecoder}. This will be called on
* the same thread as {@code decodeBitmap} before that method returns.
* This is required in order to change any of the default settings.
* @return Bitmap containing the image.
* @throws IOException if {@code src} is not found, is an unsupported
* format, or cannot be decoded for any reason.
*/
@WorkerThread
@NonNull
public static Bitmap decodeBitmap(@NonNull Source src,
@NonNull OnHeaderDecodedListener listener) throws IOException {
if (listener == null) {
throw new IllegalArgumentException("listener cannot be null! "
+ "Use decodeBitmap(Source) to not have a listener");
}
return decodeBitmapImpl(src, listener);
}
@WorkerThread
@NonNull
private static Bitmap decodeBitmapImpl(@NonNull Source src,
@Nullable OnHeaderDecodedListener listener) throws IOException {
try (ImageDecoder decoder = src.createImageDecoder()) {
decoder.mSource = src;
decoder.callHeaderDecoded(listener, src);
// this call potentially manipulates the decoder so it must be performed prior to
// decoding the bitmap
final int srcDensity = decoder.computeDensity(src);
Bitmap bm = decoder.decodeBitmapInternal();
bm.setDensity(srcDensity);
Rect padding = decoder.mOutPaddingRect;
if (padding != null) {
byte[] np = bm.getNinePatchChunk();
if (np != null && NinePatch.isNinePatchChunk(np)) {
nGetPadding(decoder.mNativePtr, padding);
}
}
return bm;
}
}
}