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标题: Picasso使用简介及分析（6） [打印本页]

作者: look_w 时间: 2019-2-18 19:55 标题: Picasso使用简介及分析（6）

6.根据不同的加载路径，选择合适的RequestHandler来创建BitmapHunter

static BitmapHunter forRequest(Picasso picasso, Dispatcher dispatcher, Cache cache, Stats stats, Action action) {
      Request request = action.getRequest();
      //Picasso中默认保存了一个集合，里面存储了每一类图片的加载，判断和处理逻辑，比如网络图片，资源图片，硬盘图片，照片等
      List<RequestHandler> requestHandlers = picasso.getRequestHandlers();
      // Index-based loop to avoid allocating an iterator.
      //noinspection ForLoopReplaceableByForEach
      for (int i = 0, count = requestHandlers.size(); i < count; i++) {
      RequestHandler requestHandler = requestHandlers.get(i);
      //它会通过request中url的scheme来判断该使用哪一个RequestHandler
      if (requestHandler.canHandleRequest(request)) {
            return new BitmapHunter(picasso, dispatcher, cache, stats, action, requestHandler);
      }
      }
   return new BitmapHunter(picasso, dispatcher, cache, stats, action, ERRORING_HANDLER);}

7. BitmapHunter被提交到线程池之后，接下来就该run方法执行了

@Override
public void run() {
   try {
   updateThreadName(data);
   ...
   }
   //重点！！！
   result = hunt();
   //得到bitmap后，执行Dispater中的方法
   if (result == null) {
      dispatcher.dispatchFailed(this);
   } else {
      dispatcher.dispatchComplete(this);
   }
} catch (Downloader.ResponseException e) {
      if (!e.localCacheOnly || e.responseCode != 504) {
      ...
      }
      dispatcher.dispatchFailed(this);
   } catch (IOException e) {//重试
      ...
      dispatcher.dispatchRetry(this);
   } catch (OutOfMemoryError e) {//OOM异常的处理
      StringWriter writer = new StringWriter();
      stats.createSnapshot().dump(new PrintWriter(writer));
      exception = new RuntimeException(writer.toString(), e);
      dispatcher.dispatchFailed(this);
   } catch (Exception e) {
      ...
      dispatcher.dispatchFailed(this);
   } finally {
         ...
      }
   }

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