如何在Picasso中使用磁盘缓存？

这就是我做的.效果很好.

首先将OkHttp添加到app模块的gradle构建文件中:

compile 'com.squareup.picasso:picasso:2.5.2'
compile 'com.squareup.okhttp3:okhttp:3.10.0'
compile 'com.jakewharton.picasso:picasso2-okhttp3-downloader:1.1.0'

然后进行课程扩展 Application

import android.app.Application;

import com.jakewharton.picasso.OkHttp3Downloader;
import com.squareup.picasso.Picasso;

public class Global extends Application {
    @Override
    public void onCreate() {
        super.onCreate();

        Picasso.Builder builder = new Picasso.Builder(this);
        builder.downloader(new OkHttp3Downloader(this,Integer.MAX_VALUE));
        Picasso built = builder.build();
        built.setIndicatorsEnabled(true);
        built.setLoggingEnabled(true);
        Picasso.setSingletonInstance(built);

    }
}

将它添加到Manifest文件,如下所示:

<application
        android:name=".Global"
        .. >

</application>

现在像往常一样使用毕加索.没有变化.

编辑:

如果您只想使用缓存图像.像这样调用库.我注意到,如果我们不添加networkPolicy,即使缓存它们,图像也不会在完全脱机启动时显示.下面的代码解决了这个问题.

Picasso.with(this)
            .load(url)
            .networkPolicy(NetworkPolicy.OFFLINE)
            .into(imageView);

编辑#2

上面代码的问题在于,如果清除缓存,Picasso将继续在缓存中脱机查找并失败,下面的代码示例查看本地缓存,如果未找到脱机,它将联机并补充缓存.

Picasso.with(getActivity())
.load(imageUrl)
.networkPolicy(NetworkPolicy.OFFLINE)
.into(imageView, new Callback() {
    @Override
    public void onSuccess() {

    }

    @Override
    public void onError() {
        //Try again online if cache failed
        Picasso.with(getActivity())
                .load(posts.get(position).getImageUrl())
                .error(R.drawable.header)
                .into(imageView, new Callback() {
            @Override
            public void onSuccess() {

            }

            @Override
            public void onError() {
                Log.v("Picasso","Could not fetch image");
            }
        });
    }
});

对于缓存,我会使用OkHttp 拦截器来控制缓存策略.查看OkHttp库中包含的此示例.

https://github.com/square/okhttp/blob/master/samples/guide/src/main/java/com/squareup/okhttp/recipes/RewriteResponseCacheControl.java

以下是我与毕加索一起使用的方法 -

OkHttpClient okHttpClient = new OkHttpClient();
    okHttpClient.networkInterceptors().add(new Interceptor() {
        @Override
        public Response intercept(Chain chain) throws IOException {
            Response originalResponse = chain.proceed(chain.request());
            return originalResponse.newBuilder().header("Cache-Control", "max-age=" + (60 * 60 * 24 * 365)).build();
        }
    });

    okHttpClient.setCache(new Cache(mainActivity.getCacheDir(), Integer.MAX_VALUE));
    OkHttpDownloader okHttpDownloader = new OkHttpDownloader(okHttpClient);
    Picasso picasso = new Picasso.Builder(mainActivity).downloader(okHttpDownloader).build();
    picasso.load(imageURL).into(viewHolder.image);

1)Picasso默认有缓存(见ahmed hamdy的答案)

2)如果您真的必须从磁盘缓存然后网络中获取图像,我建议您编写自己的下载器:

public class OkHttpDownloaderDiskCacheFirst extends OkHttpDownloader {
    public OkHttpDownloaderDiskCacheFirst(OkHttpClient client) {
        super(client);
    }

    @Override
    public Response load(Uri uri, int networkPolicy) throws IOException {
        Response responseDiskCache = null;
        try {
            responseDiskCache = super.load(uri, 1 << 2); //NetworkPolicy.OFFLINE
        } catch (Exception ignored){} // ignore, handle null later

        if (responseDiskCache == null || responseDiskCache.getContentLength()<=0){
            return  super.load(uri, networkPolicy); //user normal policy
        } else {
            return responseDiskCache;
        }

    }
}

在应用程序单例中,OnCreate方法将它与picasso一起使用:

        OkHttpClient okHttpClient = new OkHttpClient();

        okHttpClient.setCache(new Cache(getCacheDir(), 100 * 1024 * 1024)); //100 MB cache, use Integer.MAX_VALUE if it is too low
        OkHttpDownloader downloader = new OkHttpDownloaderDiskCacheFirst(okHttpClient); 

        Picasso.Builder builder = new Picasso.Builder(this);

        builder.downloader(downloader);

        Picasso built = builder.build();

        Picasso.setSingletonInstance(built);

3)defalut应用程序缓存文件夹不需要权限

1)第一个问题的答案:根据Picasso Doc for With()方法

从with()返回的全局默认Picasso实例使用适合大多数实现的默认值自动初始化.

LRU内存缓存可用应用程序RAM的15%

2%存储空间的磁盘缓存高达50MB但不低于5MB.

但 Disk Cache全球默认毕加索的操作仅适用于API 14+

2)第二个问题的答案是:Picasso使用HTTP客户端请求Disk Cache的操作所以你可以使自己http request header拥有产权Cache-Control与max-age 开创自己的静态毕加索实例,而不是默认的毕加索通过使用

1] HttpResponseCache(注意:仅适用于API 13+)
2] OkHttpClient(适用于所有API)

用于OkHttpClient创建自己的Static Picasso类的示例:

首先创建一个新类来获取自己的单例picasso对象

import android.content.Context;
import com.squareup.picasso.Downloader;
import com.squareup.picasso.OkHttpDownloader;
import com.squareup.picasso.Picasso;

public class PicassoCache {

    /**
     * Static Picasso Instance
     */
    private static Picasso picassoInstance = null;

    /**
     * PicassoCache Constructor
     *
     * @param context application Context
     */
    private PicassoCache (Context context) {

        Downloader downloader   = new OkHttpDownloader(context, Integer.MAX_VALUE);
        Picasso.Builder builder = new Picasso.Builder(context);
            builder.downloader(downloader);

        picassoInstance = builder.build();
    }

    /**
     * Get Singleton Picasso Instance
     *
     * @param context application Context
     * @return Picasso instance
     */
    public static Picasso getPicassoInstance (Context context) {

        if (picassoInstance == null) {

            new PicassoCache(context);
            return picassoInstance;
        }

        return picassoInstance;
    }

} 

使用你自己的单例picasso对象而不是Picasso.With()

PicassoCache.getPicassoInstance(getContext()).load(imagePath).into(imageView)

3)回答第三个问题:磁盘缓存操作不需要任何磁盘权限

参考文献:关于磁盘缓存的Github问题,@ jake-wharton已经回答了两个问题- > 问题1和问题2