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RecycleView和ListView一樣，都是做列表顯示View子項(xiàng)的控件，它比ListView更高效和自由。

解析RecycleView，Recycle View意思就是該控件只管回收和顯示View子項(xiàng)，而對(duì)于如何顯示，顯示什么，它是不關(guān)心的，這給開發(fā)過程帶來了極大的便利，比如ListView只能作為單列的列表顯示，GridView將一個(gè)界面表格化，通常情況下GridView通過強(qiáng)制View子項(xiàng)的寬度來顯示，在橫豎屏切換時(shí)的效果很差。

而RecycleView可以實(shí)現(xiàn)：

ListView的功能

GridView的功能

橫向ListView的功能

橫向ScrollView的功能

瀑布流的功能

添加和刪除View子項(xiàng)

這些功能，非常強(qiáng)大，可以看出，它幾乎可以替代所有的動(dòng)態(tài)布局控件。

這么強(qiáng)大的動(dòng)態(tài)布局控件，得益于它的高度解耦，同樣，眾所周知，高度解耦，就意味著復(fù)雜度提升，相較于ListView、GridView等控件，RecycleView才實(shí)現(xiàn)過程是相對(duì)較復(fù)雜的。

RecyclerView的適配器需要繼承自RecyclerView.Adapter，在該適配器將要面向ViewHolder，也就是說，它內(nèi)部已經(jīng)實(shí)現(xiàn)了緩存復(fù)用。

實(shí)現(xiàn)GridView功能

已經(jīng)實(shí)現(xiàn)了ListView，對(duì)于一個(gè)高度解耦的RecyclerView來說，再實(shí)現(xiàn)GridView的功能就非常簡(jiǎn)單了。

新建RecyclerViewDemo2工程。Adapter可以直接拷貝RecyclerViewDemo1中的內(nèi)容。暫時(shí)不考慮分隔線的情況下，只需要將實(shí)現(xiàn)ListView時(shí)使用的LinnerLayoutManager換成GridLayoutManager即可，只需要改動(dòng)兩行代碼。

Java Code

GridLayoutManager gridLayoutManager = new GridLayoutManager(this, 4);

recyclerView.setLayoutManager(gridLayoutManager);

非常的方便，那么，在一個(gè)界面中通過判斷屏幕方向，使用不同的顯示方式，也就順理成章了。

其他的東西都是不變的，除了布局管理器的改變之外，另一個(gè)需要注意的就是分隔線，需要重新繪制。

Java Code

package com.hqyj.dev.recyclerviewdemo2;

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.v7.widget.GridLayoutManager;

import android.support.v7.widget.RecyclerView;

import android.support.v7.widget.StaggeredGridLayoutManager;

import android.util.Log;

import android.view.View;

/**

* Created by jiyangkang on 2016/7/16 0016.

*/

public class GridItemDecoration extends

RecyclerView.ItemDecoration {

private Drawable mDivider;

private static final int[] ATTRS = new int[]{

android.R.attr.listDivider

};

public GridItemDecoration(Context context) {

final TypedArray t = context.obtainStyledAttributes(ATTRS);

mDivider = t.getDrawable(0);

t.recycle();

}

@Override

public void onDraw(Canvas c,

RecyclerView parent,

RecyclerView.State state) {

super.onDraw(c, parent, state);

drawHorizontal(c, parent);

drawVertical(c, parent);

}

//獲取列數(shù)

private int getSpanCount(RecyclerView parent) {

int spandCount = -1;

RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();

if (layoutManager instanceof GridLayoutManager) {

spandCount = ((GridLayoutManager) layoutManager).getSpanCount();

} else if (layoutManager instanceof StaggeredGridLayoutManager) {

spandCount = (

(StaggeredGridLayoutManager) layoutManager).getSpanCount();

}

return spandCount;

}

private void drawVertical(Canvas c, RecyclerView parent) {

final int childCount = parent.getChildCount();

for (int i = 0; i < childCount; i++) {

Log.d("Draw_v", "drawVertical: " + i);

final View child = parent.getChildAt(i);

final RecyclerView.LayoutParams params = (

RecyclerView.LayoutParams) child.getLayoutParams();

final int top = child.getTop() - params.topMargin;

final int bottom = child.getBottom() + params.bottomMargin;

final int left = child.getRight();

final int right = left + mDivider.getIntrinsicWidth();

mDivider.setBounds(left, top, right, bottom);

mDivider.draw(c);

}

}

private void drawHorizontal(Canvas c, RecyclerView parent) {

int childCount = parent.getChildCount();

for (int i = 0; i < childCount; i++) {

Log.d("Draw_h", "drawVertical: " + i);

final View child = parent.getChildAt(i);

final RecyclerView.LayoutParams params = (

RecyclerView.LayoutParams) child.getLayoutParams();

final int left = child.getLeft() - params.leftMargin;

final int right = child.getRight() + params.rightMargin

+ mDivider.getIntrinsicWidth();

final int top = child.getBottom() + params.bottomMargin;

final int bottom = top + mDivider.getIntrinsicHeight();

mDivider.setBounds(left, top, right, bottom);

mDivider.draw(c);

}

}

@Override

public void getItemOffsets(Rect outRect,

View view,

RecyclerView parent,

RecyclerView.State state) {

super.getItemOffsets(outRect, view, parent, state);

outRect.set(0,0,mDivider.getIntrinsicWidth(), mDivider.getIntrinsicHeight());

}

}

對(duì)View子項(xiàng)的操作和仿制ListView的時(shí)候是一致的。