项目做完终于有点自己的时间了，就想看点源码涨涨姿势，那就看看Picasso这个牛逼哄哄的图片加载框架吧，当然这个也是自己最喜欢的图片加载框架。
实际项目中可能有需求自己定制图片的缓存目录，那么就需要自定义下载器，如果我们使用with来构建Picasso 的实例的话，Picasso会通过Builder模式为我们初始化一个默认的下载器：
public Picasso build() {
Context context = this.context;
if (downloader == null) {
downloader = Utils.createDefaultDownloader(context);//初始化默认下载器
}
if (cache == null) {
cache = new LruCache(context);
}
if (service == null) {
service = new PicassoExecutorService();
}
if (transformer == null) {
transformer = RequestTransformer.IDENTITY;
}
Stats stats = new Stats(cache);
Dispatcher dispatcher = new Dispatcher(context, service, HANDLER, downloader, cache, stats);
return new Picasso(context, dispatcher, cache, listener, transformer, requestHandlers, stats,
defaultBitmapConfig, indicatorsEnabled, loggingEnabled);
}而Picasso创建的下载器会优先使用OkHttp，如果项目没有添加OkHttp依赖的话会使用HttpUrlConnection，检查是否添加依赖使用了反射来检查：
static Downloader createDefaultDownloader(Context context) {
if (SDK_INT >= GINGERBREAD) {
try {
Class.forName("okhttp3.OkHttpClient");
return OkHttp3DownloaderCreator.create(context);
} catch (ClassNotFoundException ignored) {
}
try {
Class.forName("com.squareup.okhttp.OkHttpClient");
return OkHttpDownloaderCreator.create(context);
} catch (ClassNotFoundException ignored) {
}
}
return new UrlConnectionDownloader(context);
}再跟踪下去，Picasso创建的默认下载器使用的缓存目录是：
static File createDefaultCacheDir(Context context) {
File cache = new File(context.getApplicationContext().getCacheDir(), PICASSO_CACHE);
if (!cache.exists()) {
//noinspection ResultOfMethodCallIgnored
cache.mkdirs();
}
return cache;
}即data/data/packagename/...，那么我们想把图片缓存到SD卡就需要自己定义下载器并设置缓存目录，下面只是把源码稍微改了下：
import android.annotation.TargetApi;
import android.content.Context;
import android.net.Uri;
import android.os.StatFs;
import android.support.annotation.NonNull;
import android.support.annotation.VisibleForTesting; import com.squareup.picasso.Downloader;
import com.squareup.picasso.NetworkPolicy; import java.io.File;
import java.io.IOException; import okhttp3.Cache;
import okhttp3.CacheControl;
import okhttp3.Call;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.ResponseBody; import static android.os.Build.VERSION.SDK_INT;
import static android.os.Build.VERSION_CODES.JELLY_BEAN_MR2; public final class OkHttp3Downloader implements Downloader {
private final Call.Factory client;
private final Cache cache;
private boolean sharedClient = true;
private static final String PICASSO_CACHE = "picasso-cache";
private static final int MIN_DISK_CACHE_SIZE = 5 * 1024 * 1024; // 5MB
private static final int MAX_DISK_CACHE_SIZE = 50 * 1024 * 1024; // 50MB private static File createDefaultCacheDir(Context context) {
File cache = new File(context.getApplicationContext().getCacheDir(), PICASSO_CACHE);
if (!cache.exists()) {
//noinspection ResultOfMethodCallIgnored
cache.mkdirs();
}
return cache;
} @TargetApi(JELLY_BEAN_MR2)
private static long calculateDiskCacheSize(File dir) {
long size = MIN_DISK_CACHE_SIZE; try {
StatFs statFs = new StatFs(dir.getAbsolutePath());
//noinspection deprecation
long blockCount = SDK_INT < JELLY_BEAN_MR2 ? (long) statFs.getBlockCount() : statFs.getBlockCountLong();
//noinspection deprecation
long blockSize = SDK_INT < JELLY_BEAN_MR2 ? (long) statFs.getBlockSize() : statFs.getBlockSizeLong();
long available = blockCount * blockSize;
// Target 2% of the total space.
size = available / 50;
} catch (IllegalArgumentException ignored) {
} // Bound inside min/max size for disk cache.
return Math.max(Math.min(size, MAX_DISK_CACHE_SIZE), MIN_DISK_CACHE_SIZE);
} /**
* Create new downloader that uses OkHttp. This will install an image cache into your application
* cache directory.
*/
public OkHttp3Downloader(final Context context) {
this(createDefaultCacheDir(context));
} /**
* Create new downloader that uses OkHttp. This will install an image cache into the specified
* directory.
*
* @param cacheDir The directory in which the cache should be stored
*/
public OkHttp3Downloader(final File cacheDir) {
this(cacheDir, calculateDiskCacheSize(cacheDir));
} /**
* Create new downloader that uses OkHttp. This will install an image cache into your application
* cache directory.
*
* @param maxSize The size limit for the cache.
*/
public OkHttp3Downloader(final Context context, final long maxSize) {
this(createDefaultCacheDir(context), maxSize);
} /**
* Create new downloader that uses OkHttp. This will install an image cache into the specified
* directory.
*
* @param cacheDir The directory in which the cache should be stored
* @param maxSize The size limit for the cache.
*/
public OkHttp3Downloader(final File cacheDir, final long maxSize) {
this(new OkHttpClient.Builder().cache(new Cache(cacheDir, maxSize)).build());
sharedClient = false;
} /**
* Create a new downloader that uses the specified OkHttp instance. A response cache will not be
* automatically configured.
*/
public OkHttp3Downloader(OkHttpClient client) {
this.client = client;
this.cache = client.cache();
} /**
* Create a new downloader that uses the specified {@link Call.Factory} instance.
*/
public OkHttp3Downloader(Call.Factory client) {
this.client = client;
this.cache = null;
} @VisibleForTesting
Cache getCache() {
return ((OkHttpClient) client).cache();
} @Override
public Response load(@NonNull Uri uri, int networkPolicy) throws IOException {
CacheControl cacheControl = null;
if (networkPolicy != 0) {
if (NetworkPolicy.isOfflineOnly(networkPolicy)) {
cacheControl = CacheControl.FORCE_CACHE;
} else {
CacheControl.Builder builder = new CacheControl.Builder();
if (!NetworkPolicy.shouldReadFromDiskCache(networkPolicy)) {
builder.noCache();
}
if (!NetworkPolicy.shouldWriteToDiskCache(networkPolicy)) {
builder.noStore();
}
cacheControl = builder.build();
}
} Request.Builder builder = new okhttp3.Request.Builder().url(uri.toString());
if (cacheControl != null) {
builder.cacheControl(cacheControl);
} okhttp3.Response response = client.newCall(builder.build()).execute();
int responseCode = response.code();
if (responseCode >= 300) {
response.body().close();
throw new ResponseException(responseCode + " " + response.message(), networkPolicy,
responseCode);
} boolean fromCache = response.cacheResponse() != null; ResponseBody responseBody = response.body();
return new Response(responseBody.byteStream(), fromCache, responseBody.contentLength());
} @Override
public void shutdown() {
if (!sharedClient) {
if (cache != null) {
try {
cache.close();
} catch (IOException ignored) {
}
}
}
}
}
然后不要使用with实例化Picasso，而要使用builder来实例化，并设置自定义的下载器即可：
final File externalFilesDir = getExternalFilesDir(Environment.DIRECTORY_NOTIFICATIONS);
BTN.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Picasso picasso = new Picasso.Builder(MainActivity.this).downloader(new OkHttp3Downloader(externalFilesDir)).build();
picasso.load(PATH).memoryPolicy(MemoryPolicy.NO_CACHE, MemoryPolicy.NO_STORE).into(IMG);
}
});