史上最細Glide原始碼解讀(一) : 主流程分析

StringLoader 又會丟給StringLoader 中的 uriLoader 去處理 ,** StringLoader #buildLoadData 會根據model 進行篩選 **, 如果是 '/' 開頭的本地圖片會返回 null , 因為model 為 http/https 開頭 ,詳細程式碼如下java public LoadData buildLoadData( @NonNull String model, int width, int height, @NonNull Options options) { Uri uri = parseUri(model); //非http/https 的返回null if (uri == null || !uriLoader.handles(uri)) { return null; } return uriLoader.buildLoadData(uri, width, height, options); } //model 為http/https 開頭 private static Uri parseUri(String model) { Uri uri; if (TextUtils.isEmpty(model)) { return null; } else if (model.charAt(0) == '/') { uri = toFileUri(model); } else { uri = Uri.parse(model); String scheme = uri.getScheme(); if (scheme == null) { uri = toFileUri(model); } } return uri; } 經過重重的篩選就只有**StreamFactory#build() 的 StringLoader** 可以供 model 使用java public ModelLoader build(@NonNull MultiModelLoaderFactory multiFactory) { return new StringLoader<>(multiFactory.build(Uri.class, InputStream.class)); } 這樣就可以去通過StringLoader載入圖片了 ? 還沒完 , 還會通過 Uri.class 和 InputStream.class 去找到與之匹配的modelLoader ![image.png](http://p3-juejin.byteimg.com/tos-cn-i-k3u1fbpfcp/652689c806e74cdfb5a1d8f0313a660c~tplv-k3u1fbpfcp-zoom-1.image) 會找到HttpUriLoader , HttpUriLoader 又會通過 **GlideUrl.class, InputStream.class** 找到與之匹配的**HttpGlideUrlLoader**, 是不是有點俄羅斯套娃的感覺 , 一層套一層java public class HttpUriLoader implements ModelLoader { private static final Set SCHEMES = Collections.unmodifiableSet(new HashSet<>(Arrays.asList("http", "https")));

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

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

} ![image.png](http://p3-juejin.byteimg.com/tos-cn-i-k3u1fbpfcp/d6b02c3acfbd4a85a0334f5a99bf8f14~tplv-k3u1fbpfcp-zoom-1.image) HttpGlideUrlLoader 應該沒有套了吧 ? 繼續點進HttpGlideUrlLoader 檢視java public class HttpGlideUrlLoader implements ModelLoader {

/** The default factory for {@link HttpGlideUrlLoader}s. */
public static class Factory implements ModelLoaderFactory<GlideUrl, InputStream> {

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

}

} ``` 果不其然 , HttpGlideUrlLoader 的Factory#build 直接返回HttpGlideUrlLoader , 停止套娃了 經過重重篩選 ,HttpGlideUrlLoader .Factory 生成的 HttpGlideUrlLoader , 才是model 需要的loader , HttpGlideUrlLoader 會通過buildLoadData 方法生成 LoadData , 去伺服器下載圖片的原始檔就是通過LoadData完成 接下來看看HttpGlideUrlLoader #buildLoadData 方法

HttpGlideUrlLoader #buildLoadData

java public LoadData<InputStream> buildLoadData( @NonNull GlideUrl model, int width, int height, @NonNull Options options) { return new LoadData<>(url, new HttpUrlFetcher(url, timeout)); } 會new 一個 LoadData , fetcher 為 HttpUrlFetcher 回到 SourceGenerator#startNextLoad 中 java private void startNextLoad(final LoadData<?> toStart) { loadData.fetcher.loadData( // ...省略回撥 //); } 繼續更進HttpUrlFetcher # loadData ```java @Override public void loadData( @NonNull Priority priority, @NonNull DataCallback<? super InputStream> callback) { try { InputStream result = loadDataWithRedirects(glideUrl.toURL(), 0, null, glideUrl.getHeaders()); callback.onDataReady(result); } }

private InputStream loadDataWithRedirects( URL url, int redirects, URL lastUrl, Map headers) throws IOException { //...省略程式碼 // urlConnection = connectionFactory.build(url); for (Map.Entry headerEntry : headers.entrySet()) { urlConnection.addRequestProperty(headerEntry.getKey(), headerEntry.getValue()); } urlConnection.connect(); stream = urlConnection.getInputStream(); //取消直接返回null if (isCancelled) { return null; } return loadDataWithRedirects(redirectUrl, redirects + 1, url, headers); }

interface HttpUrlConnectionFactory { HttpURLConnection build(URL url) throws IOException; }

private static class DefaultHttpUrlConnectionFactory implements HttpUrlConnectionFactory {

@Override
public HttpURLConnection build(URL url) throws IOException {
    return (HttpURLConnection) url.openConnection();
}

} ``` 歷經百般阻撓 , 終於看到 從伺服器下載圖片相關的程式碼 , glide 通過系統提供的 HttpURLConnection去伺服器下載圖片的原始檔
圖片源資料下載好之後 , 會通過DataCallback 回撥到SourceGenerator#onDataReadyInternal中

SourceGenerator#onDataReadyInternal

處理圖片的源資料 java void onDataReadyInternal(LoadData<?> loadData, Object data) { DiskCacheStrategy diskCacheStrategy = helper.getDiskCacheStrategy(); if (data != null && diskCacheStrategy.isDataCacheable(loadData.fetcher.getDataSource())) { dataToCache = data; cb.reschedule(); } else { cb.onDataFetcherReady( loadData.sourceKey, data, loadData.fetcher, loadData.fetcher.getDataSource(), originalKey); } } data為InputStream , 預設快取是支援DATA_CACHE , 所以會走進if 條件內, dataToCache = data , cb 為 DecodeJob, 最終會通知EngineJob 重新將 DecodeJob丟進執行緒池中 java //SourceGenerator#onDataReadyInternal void onDataReadyInternal(LoadData<?> loadData, Object data) { DiskCacheStrategy diskCacheStrategy = helper.getDiskCacheStrategy(); if (data != null && diskCacheStrategy.isDataCacheable(loadData.fetcher.getDataSource())) { cb.reschedule(); } } //DecodeJob#reschedule public void reschedule() { runReason = RunReason.SWITCH_TO_SOURCE_SERVICE; callback.reschedule(this); } //EngineJob#reschedule public void reschedule(DecodeJob<?> job) { // Even if the job is cancelled here, it still needs to be scheduled so that it can clean itself // up. getActiveSourceExecutor().execute(job); }

再次回到DecodeJob#runWrapped

此時 runReason = RunReason.SWITCH_TO_SOURCE_SERVICE; 會直接執行runGenerators() 方法 , currentGenerator 還是原來的SourceGenerator , 所以會再執行SourceGenerator#startNext 方法 ```java class SourceGenerator implements DataFetcherGenerator, DataFetcherGenerator.FetcherReadyCallback {

private DataCacheGenerator sourceCacheGenerator;
private Object dataToCache;

@Override
public boolean startNext() {
    if (dataToCache != null) {
        Object data = dataToCache;
        dataToCache = null;
        cacheData(data);
    }
    if (sourceCacheGenerator != null && sourceCacheGenerator.startNext()) {
        return true;
    }
    return started;
}


private void cacheData(Object dataToCache) {
    try {
        Encoder<Object> encoder = helper.getSourceEncoder(dataToCache);
        DataCacheWriter<Object> writer =
            new DataCacheWriter<>(encoder, dataToCache, helper.getOptions());
        originalKey = new DataCacheKey(loadData.sourceKey, helper.getSignature());
        helper.getDiskCache().put(originalKey, writer);
    } 
    sourceCacheGenerator =
        new DataCacheGenerator(Collections.singletonList(loadData.sourceKey), helper, this);
}

}

此時 dataToCache 不為 null , 會通過**DiskCache 將源資料快取在檔案** 中 , encoder為 StreamEncoder , 將圖片快取在檔案中然後會構建出 DataCacheGenerator 接著執行**DataCacheGenerator#startNext** 方法java class DataCacheGenerator implements DataFetcherGenerator, DataFetcher.DataCallback