处理多个getView最好的方式，从一个适配器内部调用 [英] Best way to handle multiple getView calls from inside an Adapter

问题描述

我有一个的ListView 自定义 ArrayAdapter 。每一个在这个的ListView 的行都有一个图标和一些文字。这些图标下载在后台，缓存，然后使用一个回调，在各自的 ImageViews 取代。获得从高速缓存或下载缩略图的逻辑每次触发 getView （）运行。

I have a ListView with custom ArrayAdapter. Each of the row in this ListView has an icon and some text. These icons are downloaded in background,cached and then using a callback, substituted in their respective ImageViews. The logic to get a thumbnail from cache or download is triggered every time getView() runs.

现在，根据罗曼盖伊：

是绝对没有保证的   的顺序getView（）将是   所谓也不会有多少次。

"there is absolutely no guarantee on the order in which getView() will be called nor how many times."

我已经看到这种情况发生，对于连续两个大小getView（）被调用六次！的

I have seen this happen, for a row of size two getView() was being called six times!

如何更改我的code，以避免重复缩略图取-请求，并处理视图回收？

How do I change my code to avoid duplicate thumbnail-fetch-requests and also handle view recycling?

感谢。

推荐答案

从API。

public abstract View   getView  (int position, View  convertView, 
                                 ViewGroup  parent)

convertView - 旧视图重用，如果可能的话。注意：您应该检查这个观点是在使用前非空一个合适的类型和。如果它是不能转换该视图以显示正确的数据，该方法可以创建新的视图。

convertView - The old view to reuse, if possible. Note: You should check that this view is non-null and of an appropriate type before using. If it is not possible to convert this view to display the correct data, this method can create a new view.

所以，如果getView已经呼吁这个特定的指数则convertView将是从第一次调用返回的视图对象。

So if getView has already been called for this specific index then convertView will be the View object that was returned from that first call.

您可以这样做。

if(!(convertView instanceof ImageView)){
   convertView = new ImageView();
   //get image from whereever
} else {} // ImageView already created

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