NetworkImageView で画像のダウンロードを開始するのが loadImageIfNecessary() です。
https://android.googlesource.com/platform/frameworks/volley/+/master/src/com/android/volley/toolbox/NetworkImageView.java
public class NetworkImageView extends ImageView {
...
/** Local copy of the ImageLoader. */
private ImageLoader mImageLoader;
...
public void setImageUrl(String url, ImageLoader imageLoader) {
mUrl = url;
mImageLoader = imageLoader;
// The URL has potentially changed. See if we need to load it.
loadImageIfNecessary(false);
}
...
/**
* Loads the image for the view if it isn't already loaded.
* @param isInLayoutPass True if this was invoked from a layout pass, false otherwise.
*/
private void loadImageIfNecessary(final boolean isInLayoutPass) {
...
// The pre-existing content of this view didn't match the current URL. Load the new image
// from the network.
ImageContainer newContainer = mImageLoader.get(mUrl,
new ImageListener() {
@Override
public void onErrorResponse(VolleyError error) {
if (mErrorImageId != 0) {
setImageResource(mErrorImageId);
}
}
@Override
public void onResponse(final ImageContainer response, boolean isImmediate) {
// If this was an immediate response that was delivered inside of a layout
// pass do not set the image immediately as it will trigger a requestLayout
// inside of a layout. Instead, defer setting the image by posting back to
// the main thread.
if (isImmediate && isInLayoutPass) {
post(new Runnable() {
@Override
public void run() {
onResponse(response, false);
}
});
return;
}
if (response.getBitmap() != null) {
setImageBitmap(response.getBitmap());
} else if (mDefaultImageId != 0) {
setImageResource(mDefaultImageId);
}
}
});
// update the ImageContainer to be the new bitmap container.
mImageContainer = newContainer;
}
...
}
ここで ImageLoader の get(url, imageListener) を呼んでいます。ImageLoader には引数が4つの get(url, imageLoader, maxWidth, maxHeight) もあり、引数が2つの get() を呼んだ場合は、maxWidth, maxHeight には 0 が渡され、生成される Bitmap は実際の画像サイズになります。
public class ImageLoader {
...
public ImageContainer get(String requestUrl, final ImageListener listener) {
return get(requestUrl, listener, 0, 0);
}
public ImageContainer get(String requestUrl, ImageListener imageListener,
int maxWidth, int maxHeight) {
// only fulfill requests that were initiated from the main thread.
throwIfNotOnMainThread();
final String cacheKey = getCacheKey(requestUrl, maxWidth, maxHeight);
// Try to look up the request in the cache of remote images.
Bitmap cachedBitmap = mCache.getBitmap(cacheKey);
if (cachedBitmap != null) {
// Return the cached bitmap.
ImageContainer container = new ImageContainer(cachedBitmap, requestUrl, null, null);
imageListener.onResponse(container, true);
return container;
}
// The bitmap did not exist in the cache, fetch it!
ImageContainer imageContainer =
new ImageContainer(null, requestUrl, cacheKey, imageListener);
// Update the caller to let them know that they should use the default bitmap.
imageListener.onResponse(imageContainer, true);
// Check to see if a request is already in-flight.
BatchedImageRequest request = mInFlightRequests.get(cacheKey);
if (request != null) {
// If it is, add this request to the list of listeners.
request.addContainer(imageContainer);
return imageContainer;
}
// The request is not already in flight. Send the new request to the network and
// track it.
Request<?> newRequest =
new ImageRequest(requestUrl, new Listener<Bitmap>() {
@Override
public void onResponse(Bitmap response) {
onGetImageSuccess(cacheKey, response);
}
}, maxWidth, maxHeight,
Config.RGB_565, new ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
onGetImageError(cacheKey, error);
}
});
mRequestQueue.add(newRequest);
mInFlightRequests.put(cacheKey,
new BatchedImageRequest(newRequest, imageContainer));
return imageContainer;
}
}
maxWidth と maxHeight は ImageRequest のコンストラクタに渡されています。
public class ImageRequest extends Request<Bitmap> {
...
private final int mMaxWidth;
private final int mMaxHeight;
...
public ImageRequest(String url, Response.Listener<Bitmap> listener, int maxWidth, int maxHeight,
Config decodeConfig, Response.ErrorListener errorListener) {
super(Method.GET, url, errorListener);
setRetryPolicy(
new DefaultRetryPolicy(IMAGE_TIMEOUT_MS, IMAGE_MAX_RETRIES, IMAGE_BACKOFF_MULT));
mListener = listener;
mDecodeConfig = decodeConfig;
mMaxWidth = maxWidth;
mMaxHeight = maxHeight;
}
...
/**
* The real guts of parseNetworkResponse. Broken out for readability.
*/
private Response<Bitmap> doParse(NetworkResponse response) {
byte[] data = response.data;
BitmapFactory.Options decodeOptions = new BitmapFactory.Options();
Bitmap bitmap = null;
if (mMaxWidth == 0 && mMaxHeight == 0) {
decodeOptions.inPreferredConfig = mDecodeConfig;
bitmap = BitmapFactory.decodeByteArray(data, 0, data.length, decodeOptions);
} else {
// If we have to resize this image, first get the natural bounds.
decodeOptions.inJustDecodeBounds = true;
BitmapFactory.decodeByteArray(data, 0, data.length, decodeOptions);
int actualWidth = decodeOptions.outWidth;
int actualHeight = decodeOptions.outHeight;
// Then compute the dimensions we would ideally like to decode to.
int desiredWidth = getResizedDimension(mMaxWidth, mMaxHeight,
actualWidth, actualHeight);
int desiredHeight = getResizedDimension(mMaxHeight, mMaxWidth,
actualHeight, actualWidth);
// Decode to the nearest power of two scaling factor.
decodeOptions.inJustDecodeBounds = false;
// TODO(ficus): Do we need this or is it okay since API 8 doesn't support it?
// decodeOptions.inPreferQualityOverSpeed = PREFER_QUALITY_OVER_SPEED;
decodeOptions.inSampleSize =
findBestSampleSize(actualWidth, actualHeight, desiredWidth, desiredHeight);
Bitmap tempBitmap =
BitmapFactory.decodeByteArray(data, 0, data.length, decodeOptions);
// If necessary, scale down to the maximal acceptable size.
if (tempBitmap != null && (tempBitmap.getWidth() > desiredWidth ||
tempBitmap.getHeight() > desiredHeight)) {
bitmap = Bitmap.createScaledBitmap(tempBitmap,
desiredWidth, desiredHeight, true);
tempBitmap.recycle();
} else {
bitmap = tempBitmap;
}
}
if (bitmap == null) {
return Response.error(new ParseError(response));
} else {
return Response.success(bitmap, HttpHeaderParser.parseCacheHeaders(response));
}
}
}
ImageRequest の doParse() で、mMaxWidth == 0 && mMaxHeight == 0 のときはバイト配列をそのまま Bitmap にしているのがわかりますね。それ以外のときは BitmapFactory.Options の inJustDecodeBounds や inSampleSize を使って Bitmap をスケールしています。
以下では、View のサイズがわかっている場合はそのサイズを使い、わからないときは画面サイズを指定するようにしてみました。
public class NetworkImageView extends ImageView {
...
private void loadImageIfNecessary(final boolean isInLayoutPass) {
int width = getWidth();
int height = getHeight();
...
DisplayMetrics metrics = getResources().getDisplayMetrics();
int w = width > 0 ? width : metrics.widthPixels;
int h = height > 0 ? height : metrics.heightPixels;
// The pre-existing content of this view didn't match the current URL. Load the new image
// from the network.
ImageContainer newContainer = mImageLoader.get(mUrl,
new ImageListener() {
@Override
public void onErrorResponse(VolleyError error) {
if (mErrorImageId != 0) {
setImageResource(mErrorImageId);
}
}
@Override
public void onResponse(final ImageContainer response, boolean isImmediate) {
// If this was an immediate response that was delivered inside of a layout
// pass do not set the image immediately as it will trigger a requestLayout
// inside of a layout. Instead, defer setting the image by posting back to
// the main thread.
if (isImmediate && isInLayoutPass) {
post(new Runnable() {
@Override
public void run() {
onResponse(response, false);
}
});
return;
}
if (response.getBitmap() != null) {
setImageBitmap(response.getBitmap());
} else if (mDefaultImageId != 0) {
setImageResource(mDefaultImageId);
}
}
}, w, h);
// update the ImageContainer to be the new bitmap container.
mImageContainer = newContainer;
}
}
