源码版本 Glide 4.8.0
ResourceTranscoder
ResourceTranscoder 是 Glide 内类型转换器的抽象接口，表示资源从一种类型转换为另一种类型。泛型 Z 表示转换前资源的原始类型，泛型 R 表示资源转换后的目标类型。
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public interface ResourceTranscoder<Z, R> {
// 子类实现此方法，根据既定规则和传入参数返回转换结果
@Nullable
Resource<R> transcode(@NonNull Resource<Z> toTranscode, @NonNull Options options);
}
ResourceTranscoder 的子类实现一共有5种：
BitmapBytesTranscoder
转换 Bitmap 资源为字节数组
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public class BitmapBytesTranscoder implements ResourceTranscoder<Bitmap, byte[]> {
private final Bitmap.CompressFormat compressFormat;
private final int quality;
public BitmapBytesTranscoder() {
// 默认转换为JPEG，压缩质量100，该质量相当于最轻量的压缩，而非不压缩
this(Bitmap.CompressFormat.JPEG, 100);
}
@SuppressWarnings("WeakerAccess")
public BitmapBytesTranscoder(@NonNull Bitmap.CompressFormat compressFormat, int quality) {
this.compressFormat = compressFormat;
this.quality = quality;
}
@Nullable
@Override
public Resource<byte[]> transcode(@NonNull Resource<Bitmap> toTranscode,
@NonNull Options options) {
// 创建输出流
ByteArrayOutputStream os = new ByteArrayOutputStream();
// 调用Bitmap的compress方法，结果写入os
toTranscode.get().compress(compressFormat, quality, os);
// 回收Bitmap
toTranscode.recycle();
return new BytesResource(os.toByteArray());
}
}
BitmapDrawableTranscoder
转换 Bitmap 资源为 BitmapDrawable
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public class BitmapDrawableTranscoder implements ResourceTranscoder<Bitmap, BitmapDrawable> {
private final Resources resources;
@SuppressWarnings("unused")
public BitmapDrawableTranscoder(@NonNull Context context) {
this(context.getResources());
}
// @deprecated Use {@link #BitmapDrawableTranscoder(Resources)}, {@code bitmapPool} is unused.
@Deprecated
public BitmapDrawableTranscoder(
@NonNull Resources resources, @SuppressWarnings("unused") BitmapPool bitmapPool) {
this(resources);
}
public BitmapDrawableTranscoder(@NonNull Resources resources) {
this.resources = Preconditions.checkNotNull(resources);
}
@Nullable
@Override
public Resource<BitmapDrawable> transcode(@NonNull Resource<Bitmap> toTranscode,
@NonNull Options options) {
return LazyBitmapDrawableResource.obtain(resources, toTranscode);
}
}
DrawableBytesTranscoder
转换 Drawable 资源为字节数组
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public final class DrawableBytesTranscoder implements ResourceTranscoder<Drawable, byte[]> {
private final BitmapPool bitmapPool;
private final ResourceTranscoder<Bitmap, byte[]> bitmapBytesTranscoder;
private final ResourceTranscoder<GifDrawable, byte[]> gifDrawableBytesTranscoder;
public DrawableBytesTranscoder(
@NonNull BitmapPool bitmapPool,
@NonNull ResourceTranscoder<Bitmap, byte[]> bitmapBytesTranscoder,
@NonNull ResourceTranscoder<GifDrawable, byte[]> gifDrawableBytesTranscoder) {
this.bitmapPool = bitmapPool;
this.bitmapBytesTranscoder = bitmapBytesTranscoder;
this.gifDrawableBytesTranscoder = gifDrawableBytesTranscoder;
}
@Nullable
@Override
public Resource<byte[]> transcode(@NonNull Resource<Drawable> toTranscode,
@NonNull Options options) {
Drawable drawable = toTranscode.get();
if (drawable instanceof BitmapDrawable) {
return bitmapBytesTranscoder.transcode(
BitmapResource.obtain(((BitmapDrawable) drawable).getBitmap(), bitmapPool), options);
} else if (drawable instanceof GifDrawable) {
return gifDrawableBytesTranscoder.transcode(toGifDrawableResource(toTranscode), options);
}
return null;
}
@SuppressWarnings("unchecked")
@NonNull
private static Resource<GifDrawable> toGifDrawableResource(@NonNull Resource<Drawable> resource) {
return (Resource<GifDrawable>) (Resource<?>) resource;
}
}
GifDrawableBytesTranscoder
把 com.bumptech.glide.load.resource.gif.GifDrawable 资源转换为字节数组
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public class GifDrawableBytesTranscoder implements ResourceTranscoder<GifDrawable, byte[]> {
@Nullable
@Override
public Resource<byte[]> transcode(@NonNull Resource<GifDrawable> toTranscode,
@NonNull Options options) {
GifDrawable gifData = toTranscode.get();
ByteBuffer byteBuffer = gifData.getBuffer();
return new BytesResource(ByteBufferUtil.toBytes(byteBuffer));
}
}
UnitTranscoder
ResourceTranscoder 的实现最简单，输入和输出类型完全相同
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public class UnitTranscoder<Z> implements ResourceTranscoder<Z, Z> {
// 本实现类的单例
private static final UnitTranscoder<?> UNIT_TRANSCODER = new UnitTranscoder<>();
@SuppressWarnings("unchecked")
public static <Z> ResourceTranscoder<Z, Z> get() {
return (ResourceTranscoder<Z, Z>) UNIT_TRANSCODER;
}
@Nullable
@Override
public Resource<Z> transcode(@NonNull Resource<Z> toTranscode, @NonNull Options options) {
// 直接返回传入对象
return toTranscode;
}
}