在RecyclerView中，我们可以通过LayoutManager控制其布局的显示方式，实现横向ListView、GridView、瀑布流等常见效果.
首先我们来看一看RecyclerView.LayoutManager的继承结构：
RecyclerView.LayoutManager是一个抽象类，其直接的实现类有LinearLayoutManager、StaggeredGridLayoutManager，而LinearLayoutManager也有一个子类GridLayoutManager.
1）通过LinearLayoutManager：我们可以实现横向、纵向的列表效果
2）通过GridLayoutManager：我们可以实现像GridView一样的网格布局
3）通过StaggeredGridLayoutManager：我们可以实现瀑布流的效果
一、LinearLayoutManager
1、纵向ListView效果
2、横向ListView效果
item的布局中TextView的android:layout_width，android:layout_height对调
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:background="#ff33b5e5"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:id="@+id/tv"
android:layout_width="40dp"
android:layout_height="match_parent"
android:gravity="center"
tools:text="别看了，我就是一个TextView" />
</RelativeLayout>
layoutManager = new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
//分隔线也改个方向
mRecyclerView.addItemDecoration(new DividerItemDecoration(this,DividerItemDecoration.HORIZONTAL));
ok，就是这么简单，看一下效果图
是不是很简单！！！
二、GridLayoutManager
1、构造方法
public GridLayoutManager(Context context, int spanCount) {
super(context);
setSpanCount(spanCount);
}
/**
* @param spanCount 网格中的列数
* @param orientation HORIZONTAL或VERTICAL，实现横向GridView、纵向GridView效果
* @param reverseLayout 为true时，布局由下向上/由右向左
*/
public GridLayoutManager(Context context, int spanCount, int orientation,
boolean reverseLayout) {
super(context, orientation, reverseLayout);
setSpanCount(spanCount);
}
2、GridView效果
item的布局：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:background="#ff33b5e5"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:id="@+id/tv"
android:layout_width="match_parent"
android:layout_height="80dp"
android:gravity="center"
tools:text="别看了，我就是一个TextView" />
</RelativeLayout>
layoutManager = new GridLayoutManager(this,4);
// 系统默认的分隔线在这里就不适用了，需注释掉
效果图：
3、GridLayoutManager的分隔线
关于分隔线的原理在RecyclerView系列之二：添加分隔线中已经介绍了，今天这里介绍GridLayoutManager的分隔线.
先上效果图：
public class MyGridItemDecoration extends RecyclerView.ItemDecoration {
private static final int[] ATTRS = new int[] { android.R.attr.listDivider };
private Drawable mDivider;
public MyGridItemDecoration (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){
drawHorizontal(c, parent);
drawVertical(c, parent);
}
private int getSpanCount(RecyclerView parent){
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;
}
/**
* 确定每个分隔线的top 、bottom 、left 、right
* 例如：条目A，就确定上图2的top 、bottom 、left 、right
*/
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 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);
}
}
/**
* 确定每个item 竖向分隔线的top 、bottom 、left 、right
* 例如：条目A，就确定上图1的top 、bottom 、left 、right
*/
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 top = child.getTop() - params.topMargin;
final int bottom = child.getBottom() + params.bottomMargin;
final int left = child.getRight() + params.rightMargin;
final int right = left + mDivider.getIntrinsicWidth();
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
}
}
/**
* 是否是最后一列
*/
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;
}
/**
* 是否是最后一行
*/
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();
if (orientation == StaggeredGridLayoutManager.VERTICAL){ // StaggeredGridLayoutManager 且纵向滚动
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{// StaggeredGridLayoutManager 且横向滚动
if ((pos + 1) % spanCount == 0){// 如果是最后一行，则不需要绘制底部
return true;
}
}
}
return false;
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
int position = parent.getChildAdapterPosition(view);
int spanCount = getSpanCount(parent);
int childCount = parent.getAdapter().getItemCount();
int pos = position;
if (isLastRaw(parent, pos, 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, pos, 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());
}
}
}
Activity中：
mRecyclerView.addItemDecoration(new MyGridItemDecoration(this));
三、StaggeredGridLayoutManager
1、构造方法
/**
* @param spanCount
* 方向为VERTICAL时spanCount代表多少列
* 方向为HORIZONTAL时spanCount代表多少行
* @param orientation VERTICAL或者HORIZONTAL
*/
public StaggeredGridLayoutManager(int spanCount, int orientation) {
mOrientation = orientation;
setSpanCount(spanCount);
setAutoMeasureEnabled(mGapStrategy != GAP_HANDLING_NONE);
mLayoutState = new LayoutState();
createOrientationHelpers();
}
2、普通GridView效果
如果仅仅是把layoutManager 改变为StaggeredGridLayoutManager，item的高度还是固定一样的话，效果和网格布局就一样了
layoutManager = new StaggeredGridLayoutManager(4,StaggeredGridLayoutManager.VERTICAL);
mRecyclerView.setLayoutManager(layoutManager);
3、瀑布流效果
要实现瀑布流的效果，每个item的高度当然要不一样了
1）item布局
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#ff33b5e5">
<TextView
android:id="@+id/tv"
android:layout_width="match_parent"
android:layout_height="80dp"
android:layout_margin="3dp"
android:gravity="center"
tools:text="别看了，我就是一个TextView" />
</RelativeLayout>
2）Adapter中
public class MainAdapter extends RecyclerView.Adapter<MainAdapter.MyViewHolder> {
private Context mContext;
private List<String> mDatas;
//这里我们定义一个随机高度的集合，确定随机高度
private List<Integer> mHeights;
public MainAdapter(Context context, List<String> mDatas) {
this.mContext = context;
this.mDatas = mDatas;
//为随机高度的集合添加数据
mHeights = new ArrayList<Integer>();
for (int i = 0; i < mDatas.size(); i++){
mHeights.add( (int) (100 + Math.random() * 300));
}
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
return new MyViewHolder(LayoutInflater.from(mContext).inflate(R.layout.item_layout, parent, false));
}
/**
* 在这里为每个item动态设置高度
*/
@Override
public void onBindViewHolder(MyViewHolder holder, final int position) {
ViewGroup.LayoutParams params = holder.tv.getLayoutParams();
params.height = mHeights.get(position);
holder.itemView.setLayoutParams(params);
holder.tv.setText(mDatas.get(position));
}
@Override
public int getItemCount() {
return mDatas.size();
}
class MyViewHolder extends RecyclerView.ViewHolder {
TextView tv;
public MyViewHolder(View view) {
super(view);
tv = (TextView)itemView.findViewById(R.id.tv);
}
}
}
这里需要注意的是，虽然是随机高度，但是不要直接在onBindViewHolder设置随机高度，像下面这样：
@Override
public void onBindViewHolder(MyViewHolder holder, final int position) {
ViewGroup.LayoutParams params = holder.tv.getLayoutParams();
params.height = (int) (100 + Math.random() * 300);
holder.itemView.setLayoutParams(params);
holder.tv.setText(mDatas.get(position));
}
因为在复用时会调用onBindViewHolder()方法填充数据，如果在这里重新给item设置高度，会出现滑动过程中item高度一直变换、item还会交换位置的问题.
3）Activity中
layoutManager = new StaggeredGridLayoutManager(4,StaggeredGridLayoutManager.VERTICAL);
mRecyclerView.setLayoutManager(layoutManager);
//这里分隔线已经不再适应，在item布局文件中我已经设置了margin代替分隔线的作用
4）效果图
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