【第三篇】Volley图片加载之NetworkImageView代码分析
load_img =(NetworkImageView) findViewById(R.id.load_img);
lruImageCache =LruImageCache.getInstance();
requestQueue =Volley.newRequestQueue(this);
imageLoader =newImageLoader(requestQueue, lruImageCache);
load_img.setImageUrl(IMGURL, imageLoader);
public class NetworkImageView extends ImageView {
/** The URL of the network image to load */
private String mUrl; /**
* Resource ID of the image to be used as a placeholder until the network image is loaded.
*/
private int mDefaultImageId; /**
* Resource ID of the image to be used if the network response fails.
*/
private int mErrorImageId; /** Local copy of the ImageLoader. */
private ImageLoader mImageLoader; /** Current ImageContainer. (either in-flight or finished) */
private ImageContainer mImageContainer; public NetworkImageView(Context context) {
this(context, null);
} public NetworkImageView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
} public NetworkImageView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
} /**
* Sets URL of the image that should be loaded into this view. Note that calling this will
* immediately either set the cached image (if available) or the default image specified by
* {@link NetworkImageView#setDefaultImageResId(int)} on the view.
*
* NOTE: If applicable, {@link NetworkImageView#setDefaultImageResId(int)} and
* {@link NetworkImageView#setErrorImageResId(int)} should be called prior to calling
* this function.
*
* @param url The URL that should be loaded into this ImageView.
* @param imageLoader ImageLoader that will be used to make the request.
*/
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);
} /**
* Sets the default image resource ID to be used for this view until the attempt to load it
* completes.
*/
public void setDefaultImageResId(int defaultImage) {
mDefaultImageId = defaultImage;
} /**
* Sets the error image resource ID to be used for this view in the event that the image
* requested fails to load.
*/
public void setErrorImageResId(int errorImage) {
mErrorImageId = errorImage;
} /**
* 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.
*/
void loadImageIfNecessary(final boolean isInLayoutPass) {
int width = getWidth();
int height = getHeight(); boolean wrapWidth = false, wrapHeight = false;
if (getLayoutParams() != null) {
wrapWidth = getLayoutParams().width == LayoutParams.WRAP_CONTENT;
wrapHeight = getLayoutParams().height == LayoutParams.WRAP_CONTENT;
} // if the view's bounds aren't known yet, and this is not a wrap-content/wrap-content
// view, hold off on loading the image.
boolean isFullyWrapContent = wrapWidth && wrapHeight;
if (width == 0 && height == 0 && !isFullyWrapContent) {
return;
} // if the URL to be loaded in this view is empty, cancel any old requests and clear the
// currently loaded image.
if (TextUtils.isEmpty(mUrl)) {
if (mImageContainer != null) {
mImageContainer.cancelRequest();
mImageContainer = null;
}
setDefaultImageOrNull();
return;
} // if there was an old request in this view, check if it needs to be canceled.
if (mImageContainer != null && mImageContainer.getRequestUrl() != null) {
if (mImageContainer.getRequestUrl().equals(mUrl)) {
// if the request is from the same URL, return.
return;
} else {
// if there is a pre-existing request, cancel it if it's fetching a different URL.
mImageContainer.cancelRequest();
setDefaultImageOrNull();
}
} // Calculate the max image width / height to use while ignoring WRAP_CONTENT dimens.
int maxWidth = wrapWidth ? 0 : width;
int maxHeight = wrapHeight ? 0 : height; // 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);
}
}
}, maxWidth, maxHeight); // update the ImageContainer to be the new bitmap container.
mImageContainer = newContainer;
} private void setDefaultImageOrNull() {
if(mDefaultImageId != 0) {
setImageResource(mDefaultImageId);
}
else {
setImageBitmap(null);
}
} @Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
loadImageIfNecessary(true);
} @Override
protected void onDetachedFromWindow() {
if (mImageContainer != null) {
// If the view was bound to an image request, cancel it and clear
// out the image from the view.
mImageContainer.cancelRequest();
setImageBitmap(null);
// also clear out the container so we can reload the image if necessary.
mImageContainer = null;
}
super.onDetachedFromWindow();
} @Override
protected void drawableStateChanged() {
super.drawableStateChanged();
invalidate();
}
}
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