Glide 的离线模式

Glide 的缓存机制很好，但是有这种情况，只想获取缓存中存在的数据，不存在的也不希望去网络获取，即只利用本地数据，或者可以叫离线模式吧。

参考链接

1. Find and load cached Image in Glide
2. Ensuring That Images Loaded Only Come From Disk Cache

解决方案

利用 Glide.with(context).using(cacheOnlyStreamLoader)...
代码取自：GlideHelper

import android.content.Context;
import android.support.annotation.NonNull;
import android.widget.ImageView;

import com.bumptech.glide.Glide;
import com.bumptech.glide.Priority;
import com.bumptech.glide.load.data.DataFetcher;
import com.bumptech.glide.load.model.stream.StreamModelLoader;

import java.io.IOException;
import java.io.InputStream;

public class GlideHelper {

    /**
     * Fill an ImageView with a picture from the resources using Glide.
     *
     * @param context       the Context for where to load
     * @param imageView     the ImageView to fill with an image
     * @param resDrawableId the resource drawable id
     */
    public static void resDrawableToImageView(Context context, ImageView imageView, int resDrawableId) {
        if (context == null || imageView == null) {
            return;
        }
        Glide.with(context)
                .load(resDrawableId)
                .thumbnail(0.1f)
                .into(imageView);
    }

    /**
     * Fill an ImageView with a picture from an http link using Glide.
     *
     * @param context                  the Context for where to load
     * @param imageView                the ImageView to fill with an image
     * @param imageUrl                 the image url from which Glide should download and cache the image
     * @param placeholderDrawableResId the resource id of the image that should be used as a placeholder image
     */
    public static void urlToImageView(Context context, ImageView imageView, @NonNull String imageUrl,
                                      int placeholderDrawableResId) {
        urlToImageView(context, imageView, imageUrl, placeholderDrawableResId, false);
    }

    /**
     * Fill an ImageView with a picture from an Http link using Glide.
     *
     * @param context                  the Context for where to load
     * @param imageView                the ImageView to fill with an image
     * @param imageUrl                 the image url from which Glide should download and cache the image
     * @param placeholderDrawableResId the resource id of the image that should be used as a placeholder image
     * @param useCacheOnly             whether to only use the cache to load the pictures or allow downloading the
     *                                 picture if the picture is not found in the cache.
     */
    public static void urlToImageView(Context context, ImageView imageView, @NonNull String imageUrl,
                                      int placeholderDrawableResId, boolean useCacheOnly) {
        if (context == null || imageView == null) {
            return;
        }
        if (useCacheOnly) {
            Glide.with(context)
                    .using(cacheOnlyStreamLoader)
                    .load(imageUrl)
                    .placeholder(placeholderDrawableResId)
                    .thumbnail(0.1f)
                    .into(imageView);
            return;
        }
        Glide.with(context)
                .load(imageUrl)
                .placeholder(placeholderDrawableResId)
                .thumbnail(0.1f)
                .into(imageView);
    }


    private static final StreamModelLoader cacheOnlyStreamLoader = new StreamModelLoader() {
        @Override
        public DataFetcher getResourceFetcher(final String model, int i, int i1) {
            return new DataFetcher() {
                @Override
                public InputStream loadData(Priority priority) throws Exception {
                    throw new IOException();
                }

                @Override
                public void cleanup() {

                }

                @Override
                public String getId() {
                    return model;
                }

                @Override
                public void cancel() {

                }
            };
        }
    };
}