Android convertView，是否要使用它? [英] Android convertView, to use it or not?
问题描述
在Android中的文章提高性能的多线程中开发人员博客，Adapter.getItem()中使用convertView来显示ImageView的列表，这些列表是通过HttpRequest下载的.在Adapter.getItem()中查看.
我想知道使用convertView有什么优势?如何回收使用过的视图?已使用的视图缓存在哪里?
我问这个问题是因为我没有在项目中使用convertView，我想知道不使用它的成本.下面是我对图像的listView的实现.
我没有使用convertView，而是在Adapter.getItem()中为新视图充气.此外，我创建了一个包装器类以将职员保存在listView的每个项目中.下载图像后，它将作为位图存储在每个列表项的包装器类中(图像很小).这样，我可以避免重复下载相同的图像.而且，这也避免了多线程提高性能中讨论的竞争条件问题.一个>.但是我还是有点担心，是否有使用我的方法不好的问题?
仅供参考:@Carl Anderson推荐的文章详细介绍了convertView在适配器中的工作方式.本文建议的Romain Guy的Google IO是另一个很好的参考.
简而言之，使用convertView可以同时优化空间和时间.此外，我放弃了自己的imageDownloader并使用@CommonsWare推荐的Picasso.它像一种魅力.不重复使用convertView的问题在于，正如您所说，每次创建和填充新的View用户将一行滚动到视图中.与重用现有视图相比，创建和扩展视图要花费大量时间，并且您肯定为此付出了性能上的损失.
我的应用程序执行类似的操作-它在ListView中的行内使用ImageViews，并且这些ImageViews由在后台下载的图像填充.作为对线程错误的调查的一部分，我关闭了对Views的重用，并且这样做时的性能绝对糟糕. ListView代码针对视图重用进行了优化，如果您不赞成这样做，则会影响帧速率和可用性.
阅读此链接还帮助我更好地了解ListViews的工作方式: http://lucasr.org/2012/04/05/Performance-tips-for-androids-listview/
In the article Multithreading For Performance from Android Developer Blog, convertView is used in Adapter.getItem() to display a list of ImageView, which are downloaded through HttpRequest.Yet, I also see some Android tutorials that don't use the convertView, and just inflate a new view in Adapter.getItem().
I'm wondering what's the advantage of using convertView? How does it recycle the used view? Where are the used view cached?
I ask this question because I didn't use convertView in my project and I want to know the cost for not using it. Below is my implementation of a listView of images.
Instead of using convertView, I inflate a new view in Adapter.getItem(). Besides, I create a wrapper class to hold the staff in each item of listView. Once the image is downloaded, it will be stored as bitmap in the wrapper class for each list item(The image is small). In this way, I can avoid the duplicate downloading of the same image. And this also avoid the race condition issues talked in Multithreading For Performance. But I'm still a little worried, is there any issues that not good by using my method?
FYI: the article recommended by @Carl Anderson gives details about how convertView works in adapter. The Google IO by Romain Guy that is suggested in this article is another good reference.
In a word, using convertView is both space and time optimized. Besides, I've abandoned my own imageDownloader and use the Picasso that is recommended by @CommonsWare. It works like a charm.
The problem with not re-using the convertView is that, as you said, you are creating and inflating a new View each and every time the user scrolls a row into view. Creating and inflating a view is a huge amount of time compared to reusing existing views, and you are certainly paying a performance hit for it.
My app does something similar - it uses ImageViews inside of rows in a ListView, and those ImageViews are populated by images that are downloaded in the background. As part of my investigation into a threading bug, I turned off reuse of Views, and the performance was absolutely terrible when I did that. ListView code is optimized for view reuse, and if you don't hold up to that, your framerate and usability will suffer.
Reading this link also helped me understand a lot better how ListViews work: http://lucasr.org/2012/04/05/performance-tips-for-androids-listview/
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