android - ViewHolder 如何优化 Adapter ？

Question

我多次看到，一个自定义的Adapter通常拥有一个内部静态类ViewHolder，所以像google的demo(package com.example.android.apis.view.List14)

而且有人告诉我，这种方式可以优化代码效率。

请告诉我为什么ViewHolder可以优化代码。

Answer 1

ViewHolder 模式将每个 View 存储在标签对象中。这样您就可以避免每次调用 getView 时都调用 findViewById，但如果 convertView 不为 null，则只检索标签。

编辑:

正如@jqpubliq 正确指出的那样

a major reason avoiding findViewById is desirable is that it traverses the child views of the viewGroup that it is called on until it finds the view with the supplied id. That means this call gets progressively more expensive the more complicated your views are