在 JScrollPane 中查找可见组件的快速方法 [英] Fast way to find visible components in JScrollPane

问题描述

给定一个包含一千个组件的 JScrollPane 使用一些 LayoutManager.每个组件都可以处于加载或卸载状态.没有足够的资源供所有加载.

Given a JScrollPane containing a thousand components using some LayoutManager. Each component can be either in a loaded or unloaded state. There are not enough resources for all to be loaded.

我只想让内存中的可见组件 load() ed，而不可见组件 unload() ed.当用户滚动时，侦听器需要不断更新组件的状态:unload() 以前可见，load() 新可见.

I'd like to have only the visible components load()ed in memory, and the invisible components unload()ed. When the user scrolls, a listener needs to keep updating the components' states: unload() the previously visible, and load() the newly visible.

1. 在任何给定时刻，我如何知道哪些组件是可见的?
2. 我可以在不迭代整个一千个的情况下知道这一点吗?(就像一个高效的viewPort.getVisibleComponents())

我将准备好所有组件 Y 的排序列表，然后在运行时二进制搜索 ViewPort 的 Y 以达到一个索引，该索引可以引导我找到可见的.这失败了，因为组件 Ys 在列表准备期间都返回 0.这需要高效.

I was going to have a prepared sorted list of all component Ys, then in runtime binary search the ViewPort's Y to reach an index which may guide me to the visible ones. This failed as component Ys all returned 0 during list preparation time. This needs to be efficient.

推荐答案

为了具体起见，我将假设有 1000 条记录，每条记录由 class Record 的一个实例表示.每个这样的 Record 应该包含一个唯一的、有意义的 key，类型为 Key.

For concreteness, I will assume 1000's of records, each represented by an instance of class Record. Each such Record should contain a unique, meaningful key of type Key.

• 获取List，可能在后台任务中.

构建一列key 值的 TableModel.

Construct a one-column TableModel of the key values.

使用这个模型构造一个JTable、table.

Use this model to construct a JTable, table.

将 table 添加到合适布局左侧的 JScrollPane.

Add the table to a JScrollPane on the left side of a suitable layout.

在右侧，添加一个面板，该面板可以显示单个选定记录的详细信息.

On the right, add a panel that can Display the details of a single, selected Record.

让 Display 包含一个 ListSelectionListener，见这里a>，更新当前在 table 中选择的任何 Record 的详细信息.

Let Display contain a ListSelectionListener, seen here, that updates the details for whichever Record is currently selected in the table.

将每个选定的Record 添加到缓存，检索从存储中记录，可能在后台任务中，仅当尚未存在于缓存中时.

Add each selected Record to a cache, retrieving the Record from storage, possibly in a background task, only if not already present in the cache.

这篇关于在 JScrollPane 中查找可见组件的快速方法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！