我们把RecyclerView写成GridView样式，并把RecyclerView的item写成focusable并且有焦点框的时候，我们用焦点滚动RecyclerView的时候会发现RecyclerView的焦点跳转有bug，跟我们想要的焦点跳转规则不一致，会出现的BUG如下图：

黑色方框代表屏幕，我们从左上角的一个item往下按焦点的时候，当需要加载新的一行的时候焦点却跑到了新的一行的最后一个item上面了，（如图，本来是item1获得焦点的，结果跑到item2上面了）。

这是RecyclerView的一个BUG，记得RecyclerView刚出来的时候滚动都还有点卡顿，到了现在滚动起来还是非常流畅的，比较一个全新的艺术般的空间是需要时间来沉淀的，这个BUG我们可以重写GridLayoutManger来解决。直接看代码：

package com.wasu.cs.widget; import android.content.Context; import android.support.v7.widget.GridLayoutManager; import android.support.v7.widget.RecyclerView; import android.util.AttributeSet; import android.view.View; /** * 自定义GridLayoutManager，修改RecyelerView焦点乱跳的BUG * Created by Danxingxi on 2016/4/1. */ public class FocusGridLayoutManager extends GridLayoutManager { /** * Constructor used when layout manager is set in XML by RecyclerView attribute * "layoutManager". If spanCount is not specified in the XML, it defaults to a * single column. * * @param context * @param attrs * @param defStyleAttr * @param defStyleRes * @attr ref android.support.v7.recyclerview.R.styleable#RecyclerView_spanCount */ public FocusGridLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) { super(context, attrs, defStyleAttr, defStyleRes); } /** * Creates a vertical GridLayoutManager * * @param context Current context, will be used to access resources. * @param spanCount The number of columns in the grid */ public FocusGridLayoutManager(Context context, int spanCount) { super(context, spanCount); } /** * @param context Current context, will be used to access resources. * @param spanCount The number of columns or rows in the grid * @param orientation Layout orientation. Should be {@link #HORIZONTAL} or {@link * #VERTICAL}. * @param reverseLayout When set to true, layouts from end to start. */ public FocusGridLayoutManager(Context context, int spanCount, int orientation, boolean reverseLayout) { super(context, spanCount, orientation, reverseLayout); } /** * Return the current number of child views attached to the parent RecyclerView. * This does not include child views that were temporarily detached and/or scrapped. * * @return Number of attached children */ @Override public int getChildCount() { return super.getChildCount(); } /** * Return the child view at the given index * * @param index Index of child to return * @return Child view at index */ @Override public View getChildAt(int index) { return super.getChildAt(index); } /** * Returns the number of items in the adapter bound to the parent RecyclerView. * @return The number of items in the bound adapter */ @Override public int getItemCount() { return super.getItemCount(); } /** * Returns the item View which has or contains focus. * * @return A direct child of RecyclerView which has focus or contains the focused child. */ @Override public View getFocusedChild() { return super.getFocusedChild(); } /** * Returns the adapter position of the item represented by the given View. This does not * contain any adapter changes that might have happened after the last layout. * * @param view The view to query * @return The adapter position of the item which is rendered by this View. */ @Override public int getPosition(View view) { return super.getPosition(view); } /** * 获取列数 * @return */ @Override public int getSpanCount() { return super.getSpanCount(); } /** * Called when searching for a focusable view in the given direction has failed for the current content of the RecyclerView. * This is the LayoutManager's opportunity to populate views in the given direction to fulfill the request if it can. * The LayoutManager should attach and return the view to be focused. The default implementation returns null. * 防止当recyclerview上下滚动的时候焦点乱跳 * @param focused * @param focusDirection * @param recycler * @param state * @return */ @Override public View onFocusSearchFailed(View focused, int focusDirection, RecyclerView.Recycler recycler, RecyclerView.State state) { // Need to be called in order to layout new row/column View nextFocus = super.onFocusSearchFailed(focused, focusDirection, recycler, state); if (nextFocus == null) { return null; } /** * 获取当前焦点的位置 */ int fromPos = getPosition(focused); /** * 获取我们希望的下一个焦点的位置 */ int nextPos = getNextViewPos(fromPos, focusDirection); return findViewByPosition(nextPos); } /** * Manually detect next view to focus. * * @param fromPos from what position start to seek. * @param direction in what direction start to seek. Your regular {@code View.FOCUS_*}. * @return adapter position of next view to focus. May be equal to {@code fromPos}. */ protected int getNextViewPos(int fromPos, int direction) { int offset = calcOffsetToNextView(direction); if (hitBorder(fromPos, offset)) { return fromPos; } return fromPos + offset; } /** * Calculates position offset. * * @param direction regular {@code View.FOCUS_*}. * @return position offset according to {@code direction}. */ protected int calcOffsetToNextView(int direction) { int spanCount = getSpanCount(); int orientation = getOrientation(); if (orientation == VERTICAL) { switch (direction) { case View.FOCUS_DOWN: return spanCount; case View.FOCUS_UP: return -spanCount; case View.FOCUS_RIGHT: return 1; case View.FOCUS_LEFT: return -1; } } else if (orientation == HORIZONTAL) { switch (direction) { case View.FOCUS_DOWN: return 1; case View.FOCUS_UP: return -1; case View.FOCUS_RIGHT: return spanCount; case View.FOCUS_LEFT: return -spanCount; } } return 0; } /** * Checks if we hit borders. * * @param from from what position. * @param offset offset to new position. * @return {@code true} if we hit border. */ private boolean hitBorder(int from, int offset) { int spanCount = getSpanCount(); if (Math.abs(offset) == 1) { int spanIndex = from % spanCount; int newSpanIndex = spanIndex + offset; return newSpanIndex < 0 || newSpanIndex >= spanCount; } else { int newPos = from + offset; return newPos < 0 && newPos >= spanCount; } } }

分析：在我们从第五行往下按的时候，第六行的view是重新加载的，当新的一行的item还没有加载出来的时候，去找焦点是找不到的，找不到焦点就会调用mLayout.onFocusSearchFailed()方法，

onFocusSearchFailed方法是LayoutManager的方法，默认是返回null的，我们在自定义GridLayoutManager的时候重写此方法即可，具体的处理步骤请看到代码。在RecyclerView源代码中，onFocusSearchFailed是内部抽象类LayoutManager的一个成员方法，默认返回null。

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