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系列文章
- android tv常见问题（一）焦点查找规律
- android tv常见问题（二）如何监听ViewGroup子View的焦点状态
- android tv常见问题（三）RecyclerView的焦点记忆
- android tv常见问题（四）焦点变化时，Recyclerview是如何进行滚动的
github地址
https://github.com/Geekholt/TvFocus
目录
期望结果
Recyclerview滚动时，聚焦的item位置保持在中间。
4.1.gif
实际结果
4.2.gif
问题分析
需要在计算RecyclerView滑动距离的方法中进行重写，控制每次滑动的距离。先来看看RecyclerView原生的滑动距离计算方法。
RecyclerView#requestChildRectangleOnScreen
当RecyclerView的某个子View需要被定位在屏幕的某个矩形范围时，调用此方法。
/**
* 通过该方法设置选中的item居中
* <p>
* 最终计算出的dy，dx的实际意义就是在滚动中上下和左右滑动的距离
*
* @param child 发出请求的子View
* @param rect 子View坐标系内的矩形，即此子View希望在屏幕上的定位
* @param immediate 设为true，则禁止动画和平滑移动滚动条
* @return 进行了滚动操作的这个ViewGroup，是否处理此操作
*/
public boolean requestChildRectangleOnScreen(RecyclerView parent, View child, Rect rect,
boolean immediate) {
final int parentLeft = getPaddingLeft();
final int parentTop = getPaddingTop();
final int parentRight = getWidth() - getPaddingRight();
final int parentBottom = getHeight() - getPaddingBottom();
final int childLeft = child.getLeft() + rect.left - child.getScrollX();
final int childTop = child.getTop() + rect.top - child.getScrollY();
final int childRight = childLeft + rect.width();
final int childBottom = childTop + rect.height();
final int offScreenLeft = Math.min(0, childLeft - parentLeft);
final int offScreenTop = Math.min(0, childTop - parentTop);
final int offScreenRight = Math.max(0, childRight - parentRight);
final int offScreenBottom = Math.max(0, childBottom - parentBottom);
// Favor the "start" layout direction over the end when bringing one side or the other
// of a large rect into view. If we decide to bring in end because start is already
// visible, limit the scroll such that start won't go out of bounds.
final int dx;
if (getLayoutDirection() == View.LAYOUT_DIRECTION_RTL) {
dx = offScreenRight != 0 ? offScreenRight
: Math.max(offScreenLeft, childRight - parentRight);
} else {
dx = offScreenLeft != 0 ? offScreenLeft
: Math.min(childLeft - parentLeft, offScreenRight);
}
// Favor bringing the top into view over the bottom. If top is already visible and
// we should scroll to make bottom visible, make sure top does not go out of bounds.
final int dy = offScreenTop != 0 ? offScreenTop
: Math.min(childTop - parentTop, offScreenBottom);
if (dx != 0 || dy != 0) {
if (immediate) {
parent.scrollBy(dx, dy);
} else {
parent.smoothScrollBy(dx, dy);
}
return true;
}
return false;
}
解决方案
public boolean requestChildRectangleOnScreen(View child, Rect rect, boolean immediate) {
//计算偏移量
int selectedItemOffsetStart = 0;
int selectedItemOffsetEnd = 0;
selectedItemOffsetStart = !isVertical() ? (getFreeWidth() - child.getWidth()) : (getFreeHeight() - child.getHeight());
selectedItemOffsetStart /= 2;
selectedItemOffsetEnd = selectedItemOffsetStart;
final int parentLeft = getPaddingLeft();
final int parentTop = getPaddingTop();
final int parentRight = getWidth() - getPaddingRight();
final int parentBottom = getHeight() - getPaddingBottom();
final int childLeft = child.getLeft() + rect.left - child.getScrollX();
final int childTop = child.getTop() + rect.top - child.getScrollY();
final int childRight = childLeft + rect.width();
final int childBottom = childTop + rect.height();
final int offScreenLeft = Math.min(0, childLeft - parentLeft - mSelectedItemOffsetStart);
final int offScreenRight = Math.max(0, childRight - parentRight + mSelectedItemOffsetEnd);
final int offScreenTop = Math.min(0, childTop - parentTop - mSelectedItemOffsetStart);
final int offScreenBottom = Math.max(0, childBottom - parentBottom + mSelectedItemOffsetEnd);
// Favor the "start" layout direction over the end when bringing one side or the other
// of a large rect into view. If we decide to bring in end because start is already
// visible, limit the scroll such that start won't go out of bounds.
final int dx;
if (getLayoutDirection() == View.LAYOUT_DIRECTION_RTL) {
dx = offScreenRight != 0 ? offScreenRight
: Math.max(offScreenLeft, childRight - parentRight);
} else {
dx = offScreenLeft != 0 ? offScreenLeft
: Math.min(childLeft - parentLeft, offScreenRight);
}
// Favor bringing the top into view over the bottom. If top is already visible and
// we should scroll to make bottom visible, make sure top does not go out of bounds.
final int dy = offScreenTop != 0 ? offScreenTop
: Math.min(childTop - parentTop, offScreenBottom);
if (dx != 0 || dy != 0) {
if (immediate) {
scrollBy(dx, dy);
} else {
smoothScrollBy(dx, dy);
}
return true;
}
return false;
}
这里要注意的是，为了适配v7，需要自定义LayoutManager，不然RecyclerView的requestChildRectangleOnScreen可能无法执行。
public class V7LinearLayoutManager extends LinearLayoutManager {
public V7LinearLayoutManager(Context context) {
super(context);
}
public V7LinearLayoutManager(Context context, int orientation, boolean reverseLayout) {
super(context, orientation, reverseLayout);
}
public V7LinearLayoutManager(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr, 0);
}
@Override
public boolean requestChildRectangleOnScreen(RecyclerView parent, View child, Rect rect, boolean immediate, boolean focusedChildVisible) {
if(parent instanceof TvRecyclerView) {
return parent.requestChildRectangleOnScreen(child, rect, immediate);
}
return super.requestChildRectangleOnScreen(parent, child, rect, immediate, focusedChildVisible);
}
}
系列文章总结
- 想要改变焦点查找规则，可以关注focusSearch的过程。
- 想要监听焦点变化的回调，可以关注requestFocus的过程。
如果想要实现一套通用焦点框架，个人想法是在Android原生焦点机制的基础上做一些定制化的操作，或许并不需要完全自己去实现一套焦点框架。
TV端焦点问题的比较复杂的根本问题我认为有两点：
- 主观因素可能是我们对Android原生的焦点机制还没有特别的清楚，所以不知道如何下手去处理一些不符合预期的现象。其实这些现象如果跟着源码去看的话，会发现它的实现都是有一定道理的。
- 客观因素是某些的UI交互比较复杂，Andorid原生的焦点机制只是采用了比较折中的处理方案。没有什么语言是完美的，也没有什么框架是完美的，能满足我们需求才是最好的。所以我认为焦点问题的处理应该建立在我们有一套统一的UI交互的基础上，然后我们在去基于Android原生焦点机制做一些定制化的操作，具体如何定制化，基本上问题都可以在文中提到的几个回调接口中去处理。
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