okhttp3版 piccaso的使用

原文地址：http://blog.csdn.net/BingHongChaZuoAn/article/details/52228670

关于okhttp3版piccaso的使用，还是有很多坑的，所以本文详解下如何跳过这些坑。

首先引入jar

dependencies {    compile 'com.squareup.okhttp3:okhttp:3.3.1'    compile 'com.squareup.okhttp3:logging-interceptor:3.3.1'    compile 'com.squareup.picasso:picasso:2.5.2'}

然后是Picasso的设置

OkHttpClient okHttpClient = OkHttpClientFactory.createClient(this);        Picasso picasso = new Picasso.Builder(this)                .downloader(new OkHttp3Downloader(okHttpClient)).build();        Picasso.setSingletonInstance(picasso);

看似很简单，其实这里隐藏着几个坑。
首先，Picasso.setSingletonInstance(picasso)只能调用一次，否则会报错。所以你可以写一个单例模式，放进去，每次调用只调用一次，也可以放到application中初始化，我的就是放到application中初始化的。

其次是新版的piccaso自带了okhttp3，为什么还要创建一个okhttpClient放到OkHttp3Downloader中，是因为https的原因，因为一些主机地址是无法访问的，所以我封装了一个okHttpClient放进去，使其可以访问某些https地址。如果你不需要的话，可以直接这么用

 Picasso picasso = new Picasso.Builder(this)                .downloader(new OkHttp3Downloader(new OkHttpClient())).build();

或者

Picasso picasso = new Picasso.Builder(this)                .downloader(new OkHttp3Downloader(this)).build();

后面这两种方法 picasso就自带了缓存了。如果用第一种的话，需要缓存还要自己去设置okhttpClient的缓存。

看下 OkHttpClientFactory

public class OkHttpClientFactory {    private static OkHttpClient okHttpClient;    private static int DEFAULT_TIME_OUT = 15;    /**     * 缓存大小     */    private final static int HTTP_RESPONSE_DISK_CACHE_MAX_SIZE = 1 * 1024*1024;    public static OkHttpClient createClient(Context context) {        /*设置缓存*/        File baseDir = context.getCacheDir();        Cache cache = null;        if (baseDir != null) {            File cacheDir = new File(baseDir, "HttpResponseCache");            cache = new Cache(cacheDir, HTTP_RESPONSE_DISK_CACHE_MAX_SIZE);        }        okHttpClient = new OkHttpClient.Builder()                .addNetworkInterceptor(new HttpLoggingInterceptor().setLevel(HttpLoggingInterceptor.Level.HEADERS))                .addInterceptor(new HeaderInterceptor(new HeaderImpl(context)))                .cookieJar(new CookieManger(context))                .connectionPool(new ConnectionPool(10,5,TimeUnit.SECONDS))                .connectTimeout(DEFAULT_TIME_OUT, TimeUnit.SECONDS)                .readTimeout(DEFAULT_TIME_OUT, TimeUnit.SECONDS)                .writeTimeout(DEFAULT_TIME_OUT, TimeUnit.SECONDS)                .sslSocketFactory(HttpsHelper.getTrustedFactory(context))                .hostnameVerifier(HttpsHelper.getTrustedVerifier())                .cache(cache)                .build();        return okHttpClient;    }}

这里是自己封装的一个OkhttpClient，里面好多内容，不一一介绍了，重点看缓存。

.cache(cache)

还有一个坑就是，我也遇到了就是没有找到OkHttp3Downloader这个类。好，我把源码贴出来：

/* * Copyright (C) 2013 Square, Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * *      http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package com.squareup.picasso;import android.content.Context;import android.net.Uri;import android.support.annotation.NonNull;import android.support.annotation.VisibleForTesting;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;/** A {@link Downloader} which uses OkHttp to download images. */public final class OkHttp3Downloader implements Downloader {    private final Call.Factory client;    private final Cache cache;    private boolean sharedClient = true;    /**     * Create new downloader that uses OkHttp. This will install an image cache into your application     * cache directory.     */    public OkHttp3Downloader(final Context context) {        this(Utils.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, Utils.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(Utils.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) {                }            }        }    }}

注意，引用的时候包名不要改变，不然就找不到某些类了。看到没，OkHttp3Downloader继承的Downloader，其实你可以写一个OkHttp4Downloader，只要继承Downloader就好了。讲一下，这个OkHttp3Downloader不是我写的，我只是拷过来引用下，别误解。
使用的话很简单，例如：

 Picasso.with(this).load("http://h.hiphotos.baidu.com/image/pic/item/08f790529822720e23efdb327fcb0a46f31fabd0.jpg")                .placeholder(R.mipmap.ic_launcher)                .resize(300, 500)                .centerCrop()                .into(imageView1);

使用的例子太多了，官网也有，就不介绍了。
好了，踩坑就到这里吧！