android.support.v7.widget.,android.support.v7.widget.recyclerview

8种机械键盘轴体对比

本人程序员，要买一个写代码的键盘，请问红轴和茶轴怎么选？

RecyclerView 的用途

A flexible view for providing a limited window into a large data set.

继承关系 及 派生类1

2

3

4

5

6java.lang.Object

↳android.view.View

↳android.view.ViewGroup

↳android.support.v7.widget.RecyclerView

派生类

HorizontalGridView, VerticalGridView

基本概念Adapter:A subclass of RecyclerView.Adapter responsible for providing views that represent items in a data set.

Position:The position of a data item within an Adapter.

Index: The index of an attached child view as used in a call to getChildAt(int). Contrast with(与...截然不同的) Position.

Binding: The process of preparing a child view to display data corresponding to a position within the adapter.

Recycle (view): A view previously used to display data for a specific adapter position may be placed in a cache for later reuse to display the same type of data again later. This can drastically improve performance by skipping initial layout inflation or construction.

Scrap(废料，小片，残余物) (view): A child view that has entered into a temporarily detached state during layout. Scrap views may be reused without becoming fully detached from the parent RecyclerView, either unmodified if no rebinding is required or modified by the adapter if the view was considered dirty.

Dirty (view): A child view that must be rebound by the adapter before being displayed.

position 概念解释Positions in RecyclerView:

RecyclerView introduces an additional level of abstraction between the RecyclerView.Adapter and RecyclerView.LayoutManager to be able to detect data set changes in batches during a layout calculation(计算). This saves LayoutManager from tracking adapter changes to calculate animations. It also helps with performance because all view bindings happen at the same time and unnecessary bindings are avoided.

For this reason, there are two types of position related methods in RecyclerView:layout position: Position of an item in the latest layout calculation. This is the position from the LayoutManager’s perspective.

adapter position: Position of an item in the adapter. This is the position from the Adapter’s perspective.

These two positions are the same except the time between dispatching adapter.notify* events and calculating the updated layout.

Methods that return or receive LayoutPosition use position as of the latest layout calculation (e.g. getLayoutPosition(), findViewHolderForLayoutPosition(int)). These positions include all changes until the last layout calculation. You can rely on these positions to be consistent with what user is currently seeing on the screen. For example, if you have a list of items on the screen and user asks for the 5th element, you should use these methods as they’ll match what user is seeing.

The other set of position related methods are in the form of AdapterPosition. (e.g. getAdapterPosition(), findViewHolderForAdapterPosition(int)) You should use these methods when you need to work with up-to-date adapter positions even if they may not have been reflected to layout yet. For example, if you want to access the item in the adapter on a ViewHolder click, you should use getAdapterPosition(). Beware that these methods may not be able to calculate adapter positions if notifyDataSetChanged() has been called and new layout has not yet been calculated. For this reasons, you should carefully handle NO_POSITION or null results from these methods.

When writing a RecyclerView.LayoutManager you almost always want to use layout positions whereas when writing an RecyclerView.Adapter, you probably want to use adapter positions.

使用中的问题1

2

3recyclerView.setLayoutManager(new LinearLayoutManager(this));

recyclerView.setAdapter

这两个方法，必须都调用了，才能显示。