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三方库源码笔记(10)-Glide 你可能不知道的知识点

三方库源码笔记(10)-Glide 你可能不知道的知识点

公众号:字节数组,希望对你有所帮助 🤣🤣

对于 Android Developer 来说,很多开源库都是属于开发必备的知识点,从使用方式到实现原理再到源码解析,这些都需要我们有一定程度的了解和运用能力。所以我打算来写一系列关于开源库源码解析实战演练的文章,初定的目标是 EventBus、ARouter、LeakCanary、Retrofit、Glide、OkHttp、Coil 等七个知名开源库,希望对你有所帮助 🤣🤣

系列文章导航:

一、利用 AppGlideModule 实现默认配置

在大多数情况下 Glide 的默认配置就已经能够满足我们的需求了,像缓存池大小,磁盘缓存策略等都不需要我们主动去设置,但 Glide 也提供了 AppGlideModule 让开发者可以去实现自定义配置。对于一个 App 来说,在加载图片的时候一般都是使用同一张 placeholder,如果每次加载图片时都需要来手动设置一遍的话就显得很多余了,此时就可以通过 AppGlideModule 来设置默认的 placeholder

首先需要继承于 AppGlideModule,在 applyOptions方法中设置配置参数,然后为实现类添加 @GlideModule 注解,这样在编译阶段 Glide 就可以通过 APT 解析到我们的这一个实现类,然后将我们的配置参数设置为默认值

/**
 * 作者:leavesC
 * 时间:2020/11/5 23:16
 * 描述:
 * GitHub:https://github.com/leavesC
 */
@GlideModule
class MyAppGlideModule : AppGlideModule() {

    //用于控制是否需要从 Manifest 文件中解析配置文件
    override fun isManifestParsingEnabled(): Boolean {
        return false
    }

    override fun applyOptions(context: Context, builder: GlideBuilder) {
        builder.setDiskCache(
            //配置磁盘缓存目录和最大缓存
            DiskLruCacheFactory(
                (context.externalCacheDir ?: context.cacheDir).absolutePath,
                "imageCache",
                1024 * 1024 * 50
            )
        )
        builder.setDefaultRequestOptions {
            return@setDefaultRequestOptions RequestOptions()
                .placeholder(android.R.drawable.ic_menu_upload_you_tube)
                .error(android.R.drawable.ic_menu_call)
                .diskCacheStrategy(DiskCacheStrategy.AUTOMATIC)
                .format(DecodeFormat.DEFAULT)
                .encodeQuality(90)
        }
    }

    override fun registerComponents(context: Context, glide: Glide, registry: Registry) {

    }

}
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在编译后,我们的工程目录中就会自动生成 GeneratedAppGlideModuleImpl 这个类,该类就包含了 MyAppGlideModule

@SuppressWarnings("deprecation")
final class GeneratedAppGlideModuleImpl extends GeneratedAppGlideModule {
  private final MyAppGlideModule appGlideModule;

  public GeneratedAppGlideModuleImpl(Context context) {
    appGlideModule = new MyAppGlideModule();
    if (Log.isLoggable("Glide", Log.DEBUG)) {
      Log.d("Glide", "Discovered AppGlideModule from annotation: github.leavesc.glide.MyAppGlideModule");
    }
  }

  @Override
  public void applyOptions(@NonNull Context context, @NonNull GlideBuilder builder) {
    appGlideModule.applyOptions(context, builder);
  }

  @Override
  public void registerComponents(@NonNull Context context, @NonNull Glide glide,
      @NonNull Registry registry) {
    appGlideModule.registerComponents(context, glide, registry);
  }

  @Override
  public boolean isManifestParsingEnabled() {
    return appGlideModule.isManifestParsingEnabled();
  }

  @Override
  @NonNull
  public Set<Class<?>> getExcludedModuleClasses() {
    return Collections.emptySet();
  }

  @Override
  @NonNull
  GeneratedRequestManagerFactory getRequestManagerFactory() {
    return new GeneratedRequestManagerFactory();
  }
}
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在运行阶段,Glide 就会通过反射生成一个 GeneratedAppGlideModuleImpl 对象,然后根据我们的默认配置项来初始化 Glide 实例

 @Nullable
  @SuppressWarnings({"unchecked", "TryWithIdenticalCatches", "PMD.UnusedFormalParameter"})
  private static GeneratedAppGlideModule getAnnotationGeneratedGlideModules(Context context) {
    GeneratedAppGlideModule result = null;
    try {
      //通过反射来生成一个 GeneratedAppGlideModuleImpl 对象
      Class<GeneratedAppGlideModule> clazz =
          (Class<GeneratedAppGlideModule>)
              Class.forName("com.bumptech.glide.GeneratedAppGlideModuleImpl");
      result =
          clazz.getDeclaredConstructor(Context.class).newInstance(context.getApplicationContext());
    } catch (ClassNotFoundException e) {
      if (Log.isLoggable(TAG, Log.WARN)) {
        Log.w(
            TAG,
            "Failed to find GeneratedAppGlideModule. You should include an"
                + " annotationProcessor compile dependency on com.github.bumptech.glide:compiler"
                + " in your application and a @GlideModule annotated AppGlideModule implementation"
                + " or LibraryGlideModules will be silently ignored");
      }
      // These exceptions can't be squashed across all versions of Android.
    } catch (InstantiationException e) {
      throwIncorrectGlideModule(e);
    } catch (IllegalAccessException e) {
      throwIncorrectGlideModule(e);
    } catch (NoSuchMethodException e) {
      throwIncorrectGlideModule(e);
    } catch (InvocationTargetException e) {
      throwIncorrectGlideModule(e);
    }
    return result;
  }


 private static void initializeGlide(
      @NonNull Context context,
      @NonNull GlideBuilder builder,
      @Nullable GeneratedAppGlideModule annotationGeneratedModule) {
    Context applicationContext = context.getApplicationContext();
    ···
    if (annotationGeneratedModule != null) {
      //调用 MyAppGlideModule 的 applyOptions 方法,对 GlideBuilder 进行设置
      annotationGeneratedModule.applyOptions(applicationContext, builder);
    }
    //根据 GlideBuilder 来生成 Glide 实例
    Glide glide = builder.build(applicationContext);
    ···
    if (annotationGeneratedModule != null) {
        //配置自定义组件
        annotationGeneratedModule.registerComponents(applicationContext, glide, glide.registry);
    }
    applicationContext.registerComponentCallbacks(glide);
    Glide.glide = glide;
  }
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二、自定义网络请求组件

默认情况下,Glide 是通过 HttpURLConnection 来进行联网请求图片的,这个过程就由 HttpUrlFetcher 类来实现。HttpURLConnection 相对于我们常用的 OkHttp 来说比较原始低效,我们可以通过使用 Glide 官方提供的okhttp3-integration来将网络请求交由 OkHttp 完成

dependencies {
    implementation "com.github.bumptech.glide:okhttp3-integration:4.11.0"
}
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如果想方便后续修改的话,我们也可以将okhttp3-integration内的代码复制出来,通过 Glide 开放的 Registry 来注册一个自定义的 OkHttpStreamFetcher,这里我也提供一份 kotlin 版本的示例代码

首先需要继承于 DataFetcher,在拿到 GlideUrl 后完成网络请求,并将请求结果通过 DataCallback 回调出去

/**
 * 作者:leavesC
 * 时间:2020/11/5 23:16
 * 描述:
 * GitHub:https://github.com/leavesC
 */
class OkHttpStreamFetcher(private val client: Call.Factory, private val url: GlideUrl) :
    DataFetcher<InputStream>, Callback {

    companion object {
        private const val TAG = "OkHttpFetcher"
    }

    private var stream: InputStream? = null

    private var responseBody: ResponseBody? = null

    private var callback: DataFetcher.DataCallback<in InputStream>? = null

    @Volatile
    private var call: Call? = null

    override fun loadData(priority: Priority, callback: DataFetcher.DataCallback<in InputStream>) {
        val requestBuilder = Request.Builder().url(url.toStringUrl())
        for ((key, value) in url.headers) {
            requestBuilder.addHeader(key, value)
        }
        val request = requestBuilder.build()
        this.callback = callback
        call = client.newCall(request)
        call?.enqueue(this)
    }

    override fun onFailure(call: Call, e: IOException) {
        if (Log.isLoggable(TAG, Log.DEBUG)) {
            Log.d(TAG, "OkHttp failed to obtain result", e)
        }
        callback?.onLoadFailed(e)
    }

    override fun onResponse(call: Call, response: Response) {
        if (response.isSuccessful) {
            responseBody = response.body()
            val contentLength = Preconditions.checkNotNull(responseBody).contentLength()
            stream = ContentLengthInputStream.obtain(responseBody!!.byteStream(), contentLength)
            callback?.onDataReady(stream)
        } else {
            callback?.onLoadFailed(HttpException(response.message(), response.code()))
        }
    }

    override fun cleanup() {
        try {
            stream?.close()
        } catch (e: IOException) {
            // Ignored
        }
        responseBody?.close()
        callback = null
    }

    override fun cancel() {
        call?.cancel()
    }

    override fun getDataClass(): Class<InputStream> {
        return InputStream::class.java
    }

    override fun getDataSource(): DataSource {
        return DataSource.REMOTE
    }

}
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之后还需要继承于 ModelLoader,提供构建 OkHttpUrlLoader 的入口

/**
 * 作者:leavesC
 * 时间:2020/11/5 23:16
 * 描述:
 * GitHub:https://github.com/leavesC
 */
class OkHttpUrlLoader(private val client: Call.Factory) : ModelLoader<GlideUrl, InputStream> {

    override fun buildLoadData(
        model: GlideUrl,
        width: Int,
        height: Int,
        options: Options
    ): LoadData<InputStream> {
        return LoadData(
            model,
            OkHttpStreamFetcher(client, model)
        )
    }

    override fun handles(model: GlideUrl): Boolean {
        return true
    }

    class Factory(private val client: Call.Factory) : ModelLoaderFactory<GlideUrl, InputStream> {

        override fun build(multiFactory: MultiModelLoaderFactory): ModelLoader<GlideUrl, InputStream> {
            return OkHttpUrlLoader(client)
        }

        override fun teardown() {
            // Do nothing, this instance doesn't own the client.
        }

    }

}
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最后注册 OkHttpUrlLoader ,之后 GlideUrl 类型的请求都会交由其处理

/**
 * 作者:leavesC
 * 时间:2020/11/5 23:16
 * 描述:
 * GitHub:https://github.com/leavesC
 */
@GlideModule
class MyAppGlideModule : AppGlideModule() {

    override fun isManifestParsingEnabled(): Boolean {
        return false
    }

    override fun applyOptions(context: Context, builder: GlideBuilder) {

    }

    override fun registerComponents(context: Context, glide: Glide, registry: Registry) {
        registry.replace(
            GlideUrl::class.java,
            InputStream::class.java,
            OkHttpUrlLoader.Factory(OkHttpClient())
        )
    }

}
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三、实现图片加载进度监听

对于某些高清图片来说,可能一张就是十几MB甚至上百MB大小了,如果没有进度条的话用户可能就会等得有点难受了,这里我就提供一个基于 OkHttp 拦截器实现的监听图片加载进度的方法

首先需要对 OkHttp 原始的 ResponseBody 进行一层包装,在内部根据 contentLength已读取到的流字节数来计算当前进度值,然后向外部提供通过 imageUrl 来注册 ProgressListener 的入口

/**
 * 作者:leavesC
 * 时间:2020/11/6 21:58
 * 描述:
 * GitHub:https://github.com/leavesC
 */
internal class ProgressResponseBody constructor(
    private val imageUrl: String,
    private val responseBody: ResponseBody?
) : ResponseBody() {

    interface ProgressListener {

        fun update(progress: Int)

    }

    companion object {

        private val progressMap = mutableMapOf<String, WeakReference<ProgressListener>>()

        fun addProgressListener(url: String, listener: ProgressListener) {
            progressMap[url] = WeakReference(listener)
        }

        fun removeProgressListener(url: String) {
            progressMap.remove(url)
        }

        private const val CODE_PROGRESS = 100

        private val mainHandler by lazy {
            object : Handler(Looper.getMainLooper()) {
                override fun handleMessage(msg: Message) {
                    if (msg.what == CODE_PROGRESS) {
                        val pair = msg.obj as Pair<String, Int>
                        val progressListener = progressMap[pair.first]?.get()
                        progressListener?.update(pair.second)
                    }
                }
            }
        }

    }

    private var bufferedSource: BufferedSource? = null

    override fun contentType(): MediaType? {
        return responseBody?.contentType()
    }

    override fun contentLength(): Long {
        return responseBody?.contentLength() ?: -1
    }

    override fun source(): BufferedSource {
        if (bufferedSource == null) {
            bufferedSource = source(responseBody!!.source()).buffer()
        }
        return bufferedSource!!
    }

    private fun source(source: Source): Source {
        return object : ForwardingSource(source) {

            var totalBytesRead = 0L

            @Throws(IOException::class)
            override fun read(sink: Buffer, byteCount: Long): Long {
                val bytesRead = super.read(sink, byteCount)
                totalBytesRead += if (bytesRead != -1L) {
                    bytesRead
                } else {
                    0
                }
                val contentLength = contentLength()
                val progress = when {
                    bytesRead == -1L -> {
                        100
                    }
                    contentLength != -1L -> {
                        ((totalBytesRead * 1.0 / contentLength) * 100).toInt()
                    }
                    else -> {
                        0
                    }
                }
                mainHandler.sendMessage(Message().apply {
                    what = CODE_PROGRESS
                    obj = Pair(imageUrl, progress)
                })
                return bytesRead
            }
        }
    }

}
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然后在 Interceptor 中使用 ProgressResponseBody 对原始的 ResponseBody 多进行一层包装,将我们的 ProgressResponseBody 作为一个代理,之后再将 ProgressInterceptor 添加给 OkHttpClient 即可

/**
 * 作者:leavesC
 * 时间:2020/11/6 22:08
 * 描述:
 * GitHub:https://github.com/leavesC
 */
class ProgressInterceptor : Interceptor {

    override fun intercept(chain: Interceptor.Chain): Response {
        val request = chain.request()
        val originalResponse = chain.proceed(request)
        val url = request.url.toString()
        return originalResponse.newBuilder()
            .body(ProgressResponseBody(url, originalResponse.body))
            .build()
    }

}
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最终实现的效果:

四、自定义磁盘缓存 key

在某些时候,我们拿到的图片 Url 可能是带有时效性的,需要在 Url 的尾部加上一个 token 值,在指定时间后 token 就会失效,防止图片被盗链。这种类型的 Url 在一定时间内就需要更换 token 才能拿到图片,可是 Url 的变化就会导致 Glide 的磁盘缓存机制完全失效

https://images.pexels.com/photos/1425174/pexels-photo-1425174.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=750&w=1260&token=tokenValue
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从我的上篇文章内容可以知道,一张图片在进行磁盘缓存时必定会同时对应一个唯一 Key,这样 Glide 在后续加载同样的图片时才能复用已有的缓存文件。对于一张网络图片来说,其唯一 Key 的生成就依赖于 GlideUrl 类的 getCacheKey()方法,该方法会直接返回网络图片的 Url 字符串。如果 Url 的 token 值会一直变化,那么 Glide 就无法对应上同一张图片了,导致磁盘缓存完全失效

/**
 * @Author: leavesC
 * @Date: 2020/11/6 15:13
 * @Desc:
 * GitHub:https://github.com/leavesC
 */
public class GlideUrl implements Key {
    
  @Nullable private final String stringUrl;
    
  public GlideUrl(String url) {
    this(url, Headers.DEFAULT);
  }

  public GlideUrl(String url, Headers headers) {
    this.url = null;
    this.stringUrl = Preconditions.checkNotEmpty(url);
    this.headers = Preconditions.checkNotNull(headers);
  }
    
  public String getCacheKey() {
    return stringUrl != null ? stringUrl : Preconditions.checkNotNull(url).toString();
  }
    
}
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想要解决这个问题,就需要来手动定义磁盘缓存时的唯一 Key。这可以通过继承 GlideUrl,修改getCacheKey()方法的返回值来实现,将 Url 移除 token 键值对后的字符串作为缓存 Key 即可

/**
 * @Author: leavesC
 * @Date: 2020/11/6 15:13
 * @Desc:
 * GitHub:https://github.com/leavesC
 */
class TokenGlideUrl(private val selfUrl: String) : GlideUrl(selfUrl) {

    override fun getCacheKey(): String {
        val uri = URI(selfUrl)
        val querySplit = uri.query.split("&".toRegex())
        querySplit.forEach {
            val kv = it.split("=".toRegex())
            if (kv.size == 2 && kv[0] == "token") {
                //将包含 token 的键值对移除
                return selfUrl.replace(it, "")
            }
        }
        return selfUrl
    }

}
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然后在加载图片的时候使用 TokenGlideUrl 来传递图片 Url 即可

      Glide.with(Context).load(TokenGlideUrl(ImageUrl)).into(ImageView)
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五、如何直接拿到图片

如果想直接取得 Bitmap 而非显示在 ImageView 上的话,可以用以下同步请求的方式来获得 Bitmap。需要注意的是,submit()方法就会触发 Glide 去请求图片,此时请求操作还是运行于 Glide 内部的线程池的,但 get()操作就会直接阻塞所在线程,直到图片加载结束(不管成功与否)才会返回

            thread {
                val futureTarget = Glide.with(this)
                    .asBitmap()
                    .load(url)
                    .submit()
                val bitmap = futureTarget.get()
                runOnUiThread {
                    iv_tokenUrl.setImageBitmap(bitmap)
                }
            }
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也可以用类似的方式来拿到 File 或者 Drawable

            thread {
                val futureTarget = Glide.with(this)
                    .asFile()
                    .load(url)
                    .submit()
                val file = futureTarget.get()
                runOnUiThread {
                    showToast(file.absolutePath)
                }
            }
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Glide 也提供了以下的异步加载方式

            Glide.with(this)
                .asBitmap()
                .load(url)
                .into(object : CustomTarget<Bitmap>() {
                    override fun onLoadCleared(placeholder: Drawable?) {
                        showToast("onLoadCleared")
                    }

                    override fun onResourceReady(
                        resource: Bitmap,
                        transition: Transition<in Bitmap>?
                    ) {
                        iv_tokenUrl.setImageBitmap(resource)
                    }
                })
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六、Glide 如何实现网络监听

在上篇文章我有讲到,RequestTracker 就用于存储所有加载图片的任务,并提供了开始、暂停和重启所有任务的方法,一个常见的需要重启任务的情形就是用户的网络从无信号状态恢复正常了,此时就应该自动重启所有未完成的任务

ConnectivityMonitor  connectivityMonitor =
        factory.build(
            context.getApplicationContext(),
            new RequestManagerConnectivityListener(requestTracker));  


private class RequestManagerConnectivityListener
      implements ConnectivityMonitor.ConnectivityListener {
    @GuardedBy("RequestManager.this")
    private final RequestTracker requestTracker;

    RequestManagerConnectivityListener(@NonNull RequestTracker requestTracker) {
      this.requestTracker = requestTracker;
    }

    @Override
    public void onConnectivityChanged(boolean isConnected) {
      if (isConnected) {
        synchronized (RequestManager.this) {
          //重启未完成的任务
          requestTracker.restartRequests();
        }
      }
    }
  }
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可以看出来,RequestManagerConnectivityListener 本身就只是一个回调函数,重点还需要看 ConnectivityMonitor 是如何实现的。ConnectivityMonitor 实现类就在 DefaultConnectivityMonitorFactory 中获取,内部会判断当前应用是否具有 NETWORK_PERMISSION 权限,如果没有的话则返回一个空实现 NullConnectivityMonitor,有权限的话就返回 DefaultConnectivityMonitor,在内部根据 ConnectivityManager 来判断当前的网络连接状态

public class DefaultConnectivityMonitorFactory implements ConnectivityMonitorFactory {
  private static final String TAG = "ConnectivityMonitor";
  private static final String NETWORK_PERMISSION = "android.permission.ACCESS_NETWORK_STATE";

  @NonNull
  @Override
  public ConnectivityMonitor build(
      @NonNull Context context, @NonNull ConnectivityMonitor.ConnectivityListener listener) {
    int permissionResult = ContextCompat.checkSelfPermission(context, NETWORK_PERMISSION);
    boolean hasPermission = permissionResult == PackageManager.PERMISSION_GRANTED;
    if (Log.isLoggable(TAG, Log.DEBUG)) {
      Log.d(
          TAG,
          hasPermission
              ? "ACCESS_NETWORK_STATE permission granted, registering connectivity monitor"
              : "ACCESS_NETWORK_STATE permission missing, cannot register connectivity monitor");
    }
    return hasPermission
        ? new DefaultConnectivityMonitor(context, listener)
        : new NullConnectivityMonitor();
  }
}
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DefaultConnectivityMonitor 的逻辑比较简单,不过多赘述。我觉得比较有价值的一点是:Glide 由于使用人数众多,有比较多的开发者会反馈 issues,DefaultConnectivityMonitor 内部就对各种可能抛出 Exception 的情况进行了捕获,这样相对来说会比我们自己实现的逻辑要考虑周全得多,所以我就把 DefaultConnectivityMonitor 复制出来转为 kotlin 以便后续自己复用了

/**
 * @Author: leavesC
 * @Date: 2020/11/7 14:40
 * @Desc:
 */
internal interface ConnectivityListener {
    fun onConnectivityChanged(isConnected: Boolean)
}

internal class DefaultConnectivityMonitor(
    context: Context,
    val listener: ConnectivityListener
) {

    private val appContext = context.applicationContext

    private var isConnected = false

    private var isRegistered = false

    private val connectivityReceiver: BroadcastReceiver = object : BroadcastReceiver() {
        override fun onReceive(context: Context, intent: Intent) {
            val wasConnected = isConnected
            isConnected = isConnected(context)
            if (wasConnected != isConnected) {
                listener.onConnectivityChanged(isConnected)
            }
        }
    }

    private fun register() {
        if (isRegistered) {
            return
        }
        // Initialize isConnected.
        isConnected = isConnected(appContext)
        try {
            appContext.registerReceiver(
                connectivityReceiver,
                IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION)
            )
            isRegistered = true
        } catch (e: SecurityException) {
            e.printStackTrace()
        }
    }

    private fun unregister() {
        if (!isRegistered) {
            return
        }
        appContext.unregisterReceiver(connectivityReceiver)
        isRegistered = false
    }

    @SuppressLint("MissingPermission")
    private fun isConnected(context: Context): Boolean {
        val connectivityManager =
            context.getSystemService(Context.CONNECTIVITY_SERVICE) as? ConnectivityManager
                ?: return true
        val networkInfo = try {
            connectivityManager.activeNetworkInfo
        } catch (e: RuntimeException) {
            return true
        }
        return networkInfo != null && networkInfo.isConnected
    }

    fun onStart() {
        register()
    }

    fun onStop() {
        unregister()
    }

}
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七、GitHub

关于 Glide 的知识点扩展也介绍完了,上述的所有示例代码我也都放到 GitHub 了,欢迎 star:AndroidOpenSourceDemo

文章分类
Android