我們都知道support庫有一個DividerItemDecoration, 可以作為Item之間的分隔線(divider)。但它作用以后所有的item之間都會有這個分隔線，實際情況往往是：recyclerView中存在多種的視圖類型(viewType), 我們只是需要在某一類型的視圖后添加分隔線。
要實現這種分隔線效果并不是什么難事，既然是某一類型有這個分隔線，那在直接在這種視圖的layout文件上增加如下一個bottomLine界面元素妥妥的:
<View android:layout_width="match_parent" android:layout_height="0.5dp" android:background="@color/colorGrayLight" />
但如果添加這樣一個界面元素導致新增一層布局那感覺代價有點大。另外一種情況，如果當前這個視圖由于某種原因存在padding，而期望的分隔線是穿透整個布局的，那添加bottomLine的做法也是行不通的；還有一種情況同一類型布局在一個頁面有分隔線，在另一個頁面沒有分隔線；總之就是希望分隔線和視圖內容無關。所以我們需要一種類似DividerItemDecoration的decoration，它能針對某些viewType起作用。
先要了解一下RecyclerView.ItemDecoration，它有2個重要的回調方法：onDrawOver和getItemOffsets。onDrawOver其實是一種應用多個item的方法，所以無論如何都需要一個遍歷操作。需要理解的是getItemOffsets中outRect這個輸出型參數，雖然是一個Rect類型，但并不表示任何范圍，而只是一個item四周的間隔距離:
outRect參數各域的含義
我們思路已經很清楚了: 在getItemOffsets中判斷當前view的類型(parent.getChildViewHolder(view)), 如果是我們需要的類型設置對應的bottom；在onDrawOver中我們遍歷recyclerView的child，同樣如果是我們需要的類型將分隔線畫在對應位置上就行了；這個decoration可以針對任意一種或者幾種類型設置不種的drawable，我們當前用SparseArray存儲，key就是視圖的viewType
private final SparseArrayCompat<Drawable> mDividers = new SparseArrayCompat<>(2);
同時我們可以設置這個item的高度，當Drawable為null時相當于一個透明的間隙，不為null時具有強制指定的高度。
同樣我們還要考慮方向：layoutManager為橫向和豎向的情況，無它，只是畫的位置不同而已。
話不多說了，上代碼:
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<Drawable> mDividers = new SparseArrayCompat<>(2); private final SparseArrayCompat<Integer> 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; }}以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持VEVB武林網。
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