Android RecyclerView 的基本使用之GridView

前文实现了利用RecyclerView实现ListView，并可以任意添加分割线，在这里主要讨论一下用RecyclerView实现GridView并实现添加分割线。

这里要提到的是RecyclerView.LayoutManager这个类。

通过查阅Android API我们可以看到如下：

A LayoutManager is responsible for measuring and positioning item views within a RecyclerView as well as determining the policy for when to recycle item views that are no longer visible to the user. By changing the LayoutManager a RecyclerView can be used to implement a standard vertically scrolling list, a uniform grid, staggered grids, horizontally scrolling collections and more. Several stock layout managers are provided for general use. RecyclerView.LayoutManager继承自Object，提供了三个子类： LinearLayoutManager：A RecyclerView.LayoutManager implementation which provides similar functionality to ListView. GridLayoutManger:A RecyclerView.LayoutManager implementations that lays out items in a grid. StaggeredGridLayoutManager:A LayoutManager that lays out children in a staggered grid formation. It supports horizontal &                          vertical layout as well as an ability to layout children in reverse. 这样，要添加GridView，只要使用 public void setLayoutManager (RecyclerView.LayoutManager layout) Set the RecyclerView.LayoutManager that this RecyclerView will use. In contrast to other adapter-backed views such as ListView or GridView, RecyclerView allows client code to provide custom layout arrangements for child views. These arrangements are controlled by theRecyclerView.LayoutManager. A LayoutManager must be provided for RecyclerView to function. Several default strategies are provided for common uses such as lists and grids. Parameters layout LayoutManager to use    对于原先的分割线，是不能用了，我们重新写了DividerGridItemDecoration。 package com.example.ahuang.recyclerview; import android.content.Context; import android.content.res.TypedArray; import android.graphics.Canvas; import android.graphics.Rect; import android.graphics.drawable.Drawable; import android.support.v4.view.ViewCompat; import android.support.v7.widget.GridLayoutManager; import android.support.v7.widget.RecyclerView; import android.support.v7.widget.StaggeredGridLayoutManager; import android.view.View; /** * Created by ahuang on 2016/1/15. */ public class DividerGridItemDecoration extends RecyclerView.ItemDecoration{ private static final int[] ATTRS = new int[] { android.R.attr.listDivider }; private Drawable mDivider; public DividerGridItemDecoration(Context context) { final TypedArray a = context.obtainStyledAttributes(ATTRS); mDivider = a.getDrawable(0); a.recycle(); } @Override public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) { super.onDraw(c, parent, state); drawHorizontal(c, parent); drawVertical(c, parent); } private int getSpanCount(RecyclerView parent) { // 列数 int spanCount = -1; RecyclerView.LayoutManager layoutManager = parent.getLayoutManager(); if (layoutManager instanceof GridLayoutManager) { spanCount = ((GridLayoutManager) layoutManager).getSpanCount(); } else if (layoutManager instanceof StaggeredGridLayoutManager) { spanCount = ((StaggeredGridLayoutManager) layoutManager) .getSpanCount(); } return spanCount; } public void drawHorizontal(Canvas c, RecyclerView parent) { int childCount = parent.getChildCount(); for (int i = 0; i < childCount; i++) { final View child = parent.getChildAt(i); final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child .getLayoutParams(); final int top = parent.getPaddingTop(); final int bottom = parent.getHeight() - parent.getPaddingBottom(); final int left = child.getRight() + params.rightMargin + Math.round(ViewCompat.getTranslationX(child)); final int right = left + mDivider.getIntrinsicHeight(); mDivider.setBounds(left, top, right, bottom); mDivider.draw(c); } } public void drawVertical(Canvas c, RecyclerView parent) { final int childCount = parent.getChildCount(); for (int i = 0; i < childCount; i++) { final View child = parent.getChildAt(i); final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child .getLayoutParams(); final int left = parent.getPaddingLeft(); final int right = parent.getWidth() - parent.getPaddingRight(); final int top = child.getBottom() + params.bottomMargin + Math.round(ViewCompat.getTranslationY(child)); final int bottom = top + mDivider.getIntrinsicHeight(); mDivider.setBounds(left, top, right, bottom); mDivider.draw(c); } } private boolean isLastColum(RecyclerView parent, int pos, int spanCount, int childCount) { RecyclerView.LayoutManager layoutManager = parent.getLayoutManager(); if (layoutManager instanceof GridLayoutManager) { if ((pos + 1) % spanCount == 0)// 如果是最后一列，则不需要绘制右边 { return true; } } else if (layoutManager instanceof StaggeredGridLayoutManager) { int orientation = ((StaggeredGridLayoutManager) layoutManager) .getOrientation(); if (orientation == StaggeredGridLayoutManager.VERTICAL) { if ((pos + 1) % spanCount == 0)// 如果是最后一列，则不需要绘制右边 { return true; } } else { childCount = childCount - childCount % spanCount; if (pos >= childCount)// 如果是最后一列，则不需要绘制右边 return true; } } return false; } private boolean isLastRaw(RecyclerView parent, int pos, int spanCount, int childCount) { RecyclerView.LayoutManager layoutManager = parent.getLayoutManager(); if (layoutManager instanceof GridLayoutManager) { childCount = childCount - childCount % spanCount; if (pos >= childCount)// 如果是最后一行，则不需要绘制底部 return true; } else if (layoutManager instanceof StaggeredGridLayoutManager) { int orientation = ((StaggeredGridLayoutManager) layoutManager) .getOrientation(); // StaggeredGridLayoutManager 且纵向滚动 if (orientation == StaggeredGridLayoutManager.VERTICAL) { childCount = childCount - childCount % spanCount; // 如果是最后一行，则不需要绘制底部 if (pos >= childCount) return true; } else // StaggeredGridLayoutManager 且横向滚动 { // 如果是最后一行，则不需要绘制底部 if ((pos + 1) % spanCount == 0) { return true; } } } return false; } @Override public void getItemOffsets(Rect outRect, int itemPosition, RecyclerView parent) { super.getItemOffsets(outRect, itemPosition, parent); int spanCount = getSpanCount(parent); int childCount = parent.getAdapter().getItemCount(); if (isLastRaw(parent, itemPosition, spanCount, childCount))// 如果是最后一行，则不需要绘制底部 { outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0); } else if (isLastColum(parent, itemPosition, spanCount, childCount))// 如果是最后一列，则不需要绘制右边 { outRect.set(0, 0, 0, mDivider.getIntrinsicHeight()); } else { outRect.set(0, 0, mDivider.getIntrinsicWidth(), mDivider.getIntrinsicHeight()); } } } 在MainActivity里加入以下代码即可实现：   效果如下：                        此外，下面代码分别添加了横向滑动的GridView和竖向滑动的GridView。