Glide之旅 —— Key

最新推荐文章于 2024-05-13 19:52:30 发布

原创最新推荐文章于 2024-05-13 19:52:30 发布 · 886 阅读

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文章标签：

#android #图片 #框架

glide 专栏收录该内容

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本文深入探讨了Glide框架中的GlideUrl组件如何用于图片加载的过程。从源码角度解析了GlideUrl如何被创建及使用，并介绍了它在缓存策略中的作用。

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前言

glide是谷歌推荐的Android图片加载框架，其优秀的缓存策略、Activity的生命周期的继承、GIF图片的支持等都是为人所称道的地方。下面是用glide加载一张图片的调用。

private void loadImage() {
    Glide.with(this)
         .load("http://pic2.orsoon.com/2017/0118/20170118011032176.jpg")
         .into(ivTest);
}

那么，该框架是如何实际运作的呢，我会通过“Glide之旅”系列博客尽可能详细地将我的心得记录下来。“Glide之旅”系列文章汇总：

概述

Key（com.bumptech.glide.load.Key），顾名思义，是用来作为图片的唯一标识，那么具体又是怎样的呢？

已知实现类

Key是一个接口，其所有实现类有

com.bumptech.glide.load.resource.bitmap.BitmapDrawableTransformation
com.bumptech.glide.load.engine.prefill.BitmapPreFillRunner.UniqueKey
com.bumptech.glide.load.resource.bitmap.BitmapTransformation
com.bumptech.glide.load.resource.bitmap.CenterCrop
com.bumptech.glide.load.resource.bitmap.CenterInside
com.bumptech.glide.load.resource.bitmap.CircleCrop
com.bumptech.glide.load.engine.DataCacheKey
com.bumptech.glide.signature.EmptySignature
com.bumptech.glide.load.engine.EngineKey
com.bumptech.glide.load.resource.bitmap.FitCenter
com.bumptech.glide.load.resource.gif.GifDrawableTransformation
com.bumptech.glide.load.resource.gif.GifFrameLoader.FrameSignature
com.bumptech.glide.load.model.GlideUrl
com.bumptech.glide.signature.MediaStoreSignature
com.bumptech.glide.load.MultiTransformation<T>
com.bumptech.glide.signature.ObjectKey
com.bumptech.glide.load.Options
com.bumptech.glide.load.engine.ResourceCacheKey
com.bumptech.glide.load.resource.bitmap.RoundedCorners
com.bumptech.glide.load.resource.UnitTransformation<T>

GlideUrl

当调用前言中的loadImage()进行图片加载的时候，结合我的Glide之旅 —— DecodeJob一文中的源码流程可知，用SourceGenerator解码远程图片的时候，首先会执行到com.bumptech.glide.load.model.stream.HttpUriLoader.Factory#build(MultiModelLoaderFactory)，先来看下源码

package com.bumptech.glide.load.model.stream;

...

public class HttpUriLoader implements ModelLoader<Uri, InputStream> {

    ...

    public static class Factory implements ModelLoaderFactory<Uri, InputStream> {

        @Override
        public ModelLoader<Uri, InputStream> build(MultiModelLoaderFactory multiFactory) {
            return new HttpUriLoader(multiFactory.build(GlideUrl.class, InputStream.class));
        }

        @Override
        public void teardown() {
            // Do nothing.
        }
    }
}

那么显然，根据Glide之旅 —— Registry中介绍的获取注册项方法可知，需要在ModelLoaderRegistry数据集合中找出Entry第一个传参为GlideUrl.class，第二个传参为InputStream.class的数据项，可知符合条件的有

23. new MultiModelLoaderFactory.Entry(GlideUrl.class, InputStream.class, new HttpGlideUrlLoader.Factory())

那么，此时再来看下com.bumptech.glide.load.model.stream.HttpGlideUrlLoader的源码

package com.bumptech.glide.load.model.stream;

...

public class HttpGlideUrlLoader implements ModelLoader<GlideUrl, InputStream> {
    public static final Option<Integer> TIMEOUT = Option.memory(
            "com.bumptech.glide.load.model.stream.HttpGlideUrlLoader.Timeout", 2500);

    @Nullable
    private final ModelCache<GlideUrl, GlideUrl> modelCache;

    public HttpGlideUrlLoader() {
        this(null);
    }

    public HttpGlideUrlLoader(ModelCache<GlideUrl, GlideUrl> modelCache) {
        this.modelCache = modelCache;
    }

    @Override
    public LoadData<InputStream> buildLoadData(GlideUrl model, int width, int height,
                                               Options options) {
        GlideUrl url = model;
        if (modelCache != null) {
            url = modelCache.get(model, 0, 0);
            if (url == null) {
                modelCache.put(model, 0, 0, model);
                url = model;
            }
        }
        int timeout = options.get(TIMEOUT);
        return new LoadData<>(url, new HttpUrlFetcher(url, timeout));
    }

    @Override
    public boolean handles(GlideUrl model) {
        return true;
    }

    public static class Factory implements ModelLoaderFactory<GlideUrl, InputStream> {
        private final ModelCache<GlideUrl, GlideUrl> modelCache = new ModelCache<>(500);

        @Override
        public ModelLoader<GlideUrl, InputStream> build(MultiModelLoaderFactory multiFactory) {
            return new HttpGlideUrlLoader(modelCache);
        }

        @Override
        public void teardown() {
            // Do nothing.
        }
    }
}

可以看到，buildLoadData(GlideUrl, int, int, Options)的返回值为new LoadData<>(url, new HttpUrlFetcher(url, timeout))，其中，url就是一个用访问的图片地址转换成的GlideUrl对象

package com.bumptech.glide.load.model;

...

public interface ModelLoader<Model, Data> {
    class LoadData<Data> {
        public final Key sourceKey;
        public final List<Key> alternateKeys;
        public final DataFetcher<Data> fetcher;

        public LoadData(Key sourceKey, DataFetcher<Data> fetcher) {
            this(sourceKey, Collections.<Key>emptyList(), fetcher);
        }

        public LoadData(Key sourceKey, List<Key> alternateKeys, DataFetcher<Data> fetcher) {
            this.sourceKey = Preconditions.checkNotNull(sourceKey);
            this.alternateKeys = Preconditions.checkNotNull(alternateKeys);
            this.fetcher = Preconditions.checkNotNull(fetcher);
        }
    }

    ...

}

也就是说，该LoadData对象的sourceKey为一个GlidUrl对象，而该GlidUrl对象是有图片来源地址转换而来的，看下GlideUrl源码

package com.bumptech.glide.load.model;

...

public class GlideUrl implements Key {
    private static final String ALLOWED_URI_CHARS = "@#&=*+-_.,:!?()/~'%";
    private final Headers headers;
    @Nullable
    private final URL url;
    @Nullable
    private final String stringUrl;

    @Nullable
    private String safeStringUrl;
    @Nullable
    private URL safeUrl;
    @Nullable
    private volatile byte[] cacheKeyBytes;

    private int hashCode;

    public GlideUrl(URL url) {
        this(url, Headers.DEFAULT);
    }

    public GlideUrl(String url) {
        this(url, Headers.DEFAULT);
    }

    public GlideUrl(URL url, Headers headers) {
        this.url = Preconditions.checkNotNull(url);
        stringUrl = null;
        this.headers = Preconditions.checkNotNull(headers);
    }

    public GlideUrl(String url, Headers headers) {
        this.url = null;
        this.stringUrl = Preconditions.checkNotEmpty(url);
        this.headers = Preconditions.checkNotNull(headers);
    }

    public URL toURL() throws MalformedURLException {
        return getSafeUrl();
    }

    private URL getSafeUrl() throws MalformedURLException {
        if (safeUrl == null) {
            safeUrl = new URL(getSafeStringUrl());
        }
        return safeUrl;
    }

    public String toStringUrl() {
        return getSafeStringUrl();
    }

    private String getSafeStringUrl() {
        if (TextUtils.isEmpty(safeStringUrl)) {
            String unsafeStringUrl = stringUrl;
            if (TextUtils.isEmpty(unsafeStringUrl)) {
                unsafeStringUrl = url.toString();
            }
            safeStringUrl = Uri.encode(unsafeStringUrl, ALLOWED_URI_CHARS);
        }
        return safeStringUrl;
    }

    public Map<String, String> getHeaders() {
        return headers.getHeaders();
    }

    public String getCacheKey() {
        return stringUrl != null ? stringUrl : url.toString();
    }

    @Override
    public String toString() {
        return getCacheKey();
    }

    @Override
    public void updateDiskCacheKey(MessageDigest messageDigest) {
        messageDigest.update(getCacheKeyBytes());
    }

    private byte[] getCacheKeyBytes() {
        if (cacheKeyBytes == null) {
            cacheKeyBytes = getCacheKey().getBytes(CHARSET);
        }
        return cacheKeyBytes;
    }

    @Override
    public boolean equals(Object o) {
        if (o instanceof GlideUrl) {
            GlideUrl other = (GlideUrl) o;
            return getCacheKey().equals(other.getCacheKey())
                    && headers.equals(other.headers);
        }
        return false;
    }

    @Override
    public int hashCode() {
        if (hashCode == 0) {
            hashCode = getCacheKey().hashCode();
            hashCode = 31 * hashCode + headers.hashCode();
        }
        return hashCode;
    }
}