Android RecyclerView区分视图类型的Divider的实现
我们都知道support库有一个DividerItemDecoration, 可以作为Item之间的分隔线(divider)。但它作用以后所有的item之间都会有这个分隔线，实际情况往往是：recyclerView中存在多种的视图类型(viewType), 我们只是需要在某一类型的视图后添加分隔线。
要实现这种分隔线效果并不是什么难事，既然是某一类型有这个分隔线，那在直接在这种视图的layout文件上增加如下一个bottomLine界面元素妥妥的:
但如果添加这样一个界面元素导致新增一层布局那感觉代价有点大。另外一种情况，如果当前这个视图由于某种原因存在padding，而期望的分隔线是穿透整个布局的，那添加bottomLine的做法也是行不通的；还有一种情况同一类型布局在一个页面有分隔线，在另一个页面没有分隔线；总之就是希望分隔线和视图内容无关。所以我们需要一种类似DividerItemDecoration的decoration，它能针对某些viewType起作用。
先要了解一下RecyclerView.ItemDecoration，它有2个重要的回调方法：onDrawOver和getItemOffsets。onDrawOver其实是一种应用多个item的方法，所以无论如何都需要一个遍历操作。需要理解的是getItemOffsets中outRect这个输出型参数，虽然是一个Rect类型，但并不表示任何范围，而只是一个item四周的间隔距离:
outRect参数各域的含义
我们思路已经很清楚了:
在getItemOffsets中判断当前view的类型(parent.getChildViewHolder(view)),
如果是我们需要的类型设置对应的bottom；在onDrawOver中我们遍历recyclerView的child，同样如果是我们需要的类型将分隔线画在对应位置上就行了；这个decoration可以针对任意一种或者几种类型设置不种的drawable，我们当前用SparseArray存储，key就是视图的viewType
private final SparseArrayCompat
同时我们可以设置这个item的高度，当Drawable为null时相当于一个透明的间隙，不为null时具有强制指定的高度。
同样我们还要考虑方向：layoutManager为横向和竖向的情况，无它，只是画的位置不同而已。
话不多说了，上代码:
import android.graphics.drawable.Drawable;
import android.support.annotation.Nullable;
import android.support.v7.widget.RecyclerView;
public class ViewTypeDivider extends ItemHolderDivider {
@Override
protected int keyFrom(RecyclerView.ViewHolder holder) {
return holder.getItemViewType();
}
public ViewTypeDivider put(int viewType, Drawable drawable) {
putDrawable(viewType, drawable);
return this;
}
public ViewTypeDivider put(int viewType, @Nullable Drawable drawable, int height) {
putHeight(viewType, drawable, height);
return this;
}
}
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.support.annotation.Nullable;
import android.support.v4.util.SparseArrayCompat;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.View;
abstract class ItemHolderDivider extends RecyclerView.ItemDecoration {
private final SparseArrayCompat mDividers = new SparseArrayCompat<>(2);
private final SparseArrayCompat mHeights = new SparseArrayCompat<>(2);
protected abstract int keyFrom(RecyclerView.ViewHolder holder);
@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
final int childCount = parent.getChildCount();
final int width = parent.getWidth();
final int height = parent.getHeight();
for (int childViewIndex = 0; childViewIndex < childCount; childViewIndex++) {
final View view = parent.getChildAt(childViewIndex);
RecyclerView.ViewHolder holder = parent.getChildViewHolder(view);
int key = keyFrom(holder);
if (isVertical(parent)) {
drawBottom(c, key, (int) view.getY() + view.getHeight(), width);
drawTop(c, -key, (int) view.getY(), width);
} else {
drawRight(c, key, (int) view.getX() + view.getWidth(), height);
drawLeft(c, -key, (int) view.getX(), height);
}
}
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
RecyclerView.State state) {
RecyclerView.ViewHolder holder = parent.getChildViewHolder(view);
int key = keyFrom(holder);
if (isVertical(parent)) {
outRect.bottom = getHeight(key);
outRect.top = getHeight(-key);
} else {
outRect.right = getHeight(key);
outRect.left = getHeight(-key);
}
}
private void drawBottom(Canvas c, int key, int y, int width) {
Drawable d = mDividers.get(key);
if (d != null) {
d.setBounds(0, y, width, y + getHeight(key, d));
d.draw(c);
}
}
private void drawTop(Canvas c, int key, int y, int width) {
Drawable d = mDividers.get(key);
if (d != null) {
d.setBounds(0, y - getHeight(key, d), width, y);
d.draw(c);
}
}
private void drawRight(Canvas c, int key, int x, int height) {
Drawable d = mDividers.get(key);
if (d != null) {
d.setBounds(x, 0, x + getHeight(key, d), height);
d.draw(c);
}
}
private void drawLeft(Canvas c, int key, int x, int height) {
Drawable d = mDividers.get(key);
if (d != null) {
d.setBounds(x - getHeight(key, d), 0, x, height);
d.draw(c);
}
}
final void putDrawable(int key, Drawable drawable) {
mDividers.put(key, drawable);
}
final void putHeight(int key, @Nullable Drawable drawable, int height) {
if (drawable != null) {
mDividers.put(key, drawable);
}
mHeights.put(key, height);
}
private int getHeight(int key) {
Drawable d = mDividers.get(key);
return getHeight(key, d);
}
private int getHeight(int key, @Nullable Drawable d) {
int index = mHeights.indexOfKey(key);
return index < 0 ? d == null ? 0 : d.getIntrinsicHeight() : mHeights.valueAt(index);
}
private boolean isVertical(RecyclerView parent) {
RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
return !(layoutManager instanceof LinearLayoutManager) ||
((LinearLayoutManager) layoutManager).getOrientation() == LinearLayoutManager.VERTICAL;
}
}
