如何正确设置Volley以从URL下载图像 [英] How do I properly set up Volley to download images from a URL
问题描述
我知道Volley应该可以轻松地下载和缓存图像，但是我已经努力了好几个小时才能正确实现它.我浏览了网上以及有关凌空的许多关于stackoverflow的文章，但是我发现的所有示例似乎都不适合我.
I know Volley is supposed to make downloading and caching images mindlessly simple but yet I have been struggling for hours to properly implement it. I've looked around the net as well as the many articles on stackoverflow regarding volley but none of the examples I've found seem to work for me.
我只想使用凌空来从给定的URL下载和缓存图像，而不想执行任何HTTP JSON REST处理.仅使用给定的URL，下载位图并将其设置为imageview，然后将其添加到缓存中.
I only want to use volley to download and cache images from a given url, not to do any HTTP JSON REST handling. Just to take given urls, download the bitmaps and set them to the imageview then add them to the cache.
这是我到目前为止的最新尝试. 如何正确使用凌空加载和缓存图像?
This has been my latest attempt so far. How do I load and cache images with volley correctly?
if (data.getImageUrl() != null) {
try {
holder.thumbnail.setTag(data.getImageUrl());
Cache cache = ImgController.getInstance().getRequestQueue().getCache();
Cache.Entry entry = cache.get(data.getImageUrl());
if (entry != null) {
try {
String cImg = new String(entry.data, "UTF-8");
LruBitmapCache bitmapCache = new LruBitmapCache();
holder.thumbnail.setImageBitmap(bitmapCache.getBitmap(cImg));
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
} else {
ImageLoader imageLoader = ImgController.getInstance().getImageLoader();
imageLoader.get(data.getImageUrl(), new ImageListener() {
@Override
public void onErrorResponse(VolleyError error) {
holder.thumbnail.setImageResource(R.drawable.filler_icon);
}
@Override
public void onResponse(ImageLoader.ImageContainer response, boolean arg1) {
if (response.getBitmap() != null) {
// load image into imageview
holder.thumbnail.setImageBitmap(response.getBitmap());
}
}
});
}
return convertView;
} catch (Exception e) {
e.printStackTrace();
Log.v(DEBUG_TAG, "no image: ", e);
holder.thumbnail.setImageResource(R.drawable.filler_icon);
}
}else {
return null;
}
return convertView;
}
运行此命令时，我得到一个NullPointerException指向此行
When I run this I get a NullPointerException pointing to this line
Cache cache = ImgController.getInstance().getRequestQueue().getCache();
我已经设置了以下单例类来处理请求
I've setup the following singleton class to handle requests
public class ImgController extends Application {
public static final String TAG = ImgController.class.getSimpleName();
private RequestQueue requestQueue;
private ImageLoader imageLoader;
private static ImgController instance;
@Override
public void onCreate() {
super.onCreate();
instance = this;
}
public static synchronized ImgController getInstance(){
return instance;
}
public RequestQueue getRequestQueue(){
if(requestQueue == null){
requestQueue = Volley.newRequestQueue(getApplicationContext());
}
return this.requestQueue;
}
public ImageLoader getImageLoader(){
getRequestQueue();
if(imageLoader == null){
imageLoader = new ImageLoader(this.requestQueue, new LruBitmapCache());
}
return this.imageLoader;
}
public <T> void addToRequestQueue(Request<T> req, String tag) {
// set the default tag if tag is empty
req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
getRequestQueue().add(req);
}
public <T> void addToRequestQueue(Request<T> req) {
req.setTag(TAG);
getRequestQueue().add(req);
}
public void cancelPendingRequests(Object tag) {
if (requestQueue != null) {
requestQueue.cancelAll(tag);
}
}
}
以及以下LruBitmapCache类
as well as the following LruBitmapCache class
public class LruBitmapCache extends LruCache<String, Bitmap> implements ImageLoader.ImageCache {
public static int getDefaultLruCacheSize(){
final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
final int cacheSize = maxMemory / 8;
return cacheSize;
}
public LruBitmapCache() {
this(getDefaultLruCacheSize());
}
public LruBitmapCache(int maxSize) {
super(maxSize);
}
@Override
public Bitmap getBitmap(String url) {
return get(url);
}
@Override
public void putBitmap(String url, Bitmap bitmap) {
put (url, bitmap);
}
}
推荐答案
(对不起，英语技能很差^^;)
(Sorry for poor english skill ^^;)
Volley可以使图片的下载和缓存变得轻而易举
Volley is supposed to make downloading and caching images mindlessly simple
是的！凌空非常简单.您无需考虑缓存命中，图像加载等...
YEAH! Volley is VERY SIMPLE. you don't need to think about cache hit, image loading etc...
只需使用NetworkImageView.下面是示例.
just use NetworkImageView. Belows are example.
layout_example.xml
layout_example.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MainActivity">
<com.android.volley.toolbox.NetworkImageView
android:id="@+id/photo"
android:adjustViewBounds="true"
android:scaleType="fitCenter"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</RelativeLayout>
MainActivity.java
MainActivity.java
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.layout_example);
NetworkImageView nv = (NetworkImageView) findViewById(R.id.photo);
nv.setDefaultImageResId(R.drawable.default_image); // image for loading...
nv.setImageUrl(imageUrl, ImgController.getInstance().getImageLoader()); //ImgController from your code.
}
NetworkImageView会自动从后台队列加载图像，并在分离此视图using ImageLoader时取消请求.和ImageLoader 自动使用内存lru缓存和磁盘缓存. NetworkImageView是最适合您的解决方案.
NetworkImageView automatically loads image from background queue and cancel request when this view is detached using ImageLoader. and ImageLoader automatically uses memory lru cache and disk cache. NetworkImageView is best solution for you.
NetworkImageView
|
ImageLoader (uses `LruBitmapCache` you implemented.)
|
RequestQueue (uses `DiskBasedCache`. it is already implemented in volley.)
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