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系列文章
- android tv常見問題（一）焦點查找規律
- android tv常見問題（二）如何監聽ViewGroup子View的焦點狀態
- android tv常見問題（三）RecyclerView的焦點記憶
- android tv常見問題（四）焦點變化時，Recyclerview是如何進行滾動的
github地址
https://github.com/Geekholt/TvFocus
目錄
期望結果
Recyclerview滾動時，聚焦的item位置保持在中間。
4.1.gif
實際結果
4.2.gif
問題分析
需要在計算RecyclerView滑動距離的方法中進行重寫，控制每次滑動的距離。先來看看RecyclerView原生的滑動距離計算方法。
RecyclerView#requestChildRectangleOnScreen
當RecyclerView的某個子View需要被定位在屏幕的某個矩形范圍時，調用此方法。
/**
* 通過該方法設置選中的item居中
* <p>
* 最終計算出的dy，dx的實際意義就是在滾動中上下和左右滑動的距離
*
* @param child 發出請求的子View
* @param rect 子View坐標系內的矩形，即此子View希望在屏幕上的定位
* @param immediate 設為true，則禁止動畫和平滑移動滾動條
* @return 進行了滾動操作的這個ViewGroup，是否處理此操作
*/
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;
}
解決方案
public boolean requestChildRectangleOnScreen(View child, Rect rect, boolean immediate) {
//計算偏移量
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;
}
這里要注意的是，為了適配v7，需要自定義LayoutManager，不然RecyclerView的requestChildRectangleOnScreen可能無法執行。
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);
}
}
系列文章總結
- 想要改變焦點查找規則，可以關注focusSearch的過程。
- 想要監聽焦點變化的回調，可以關注requestFocus的過程。
如果想要實現一套通用焦點框架，個人想法是在Android原生焦點機制的基礎上做一些定制化的操作，或許并不需要完全自己去實現一套焦點框架。
TV端焦點問題的比較復雜的根本問題我認為有兩點：
- 主觀因素可能是我們對Android原生的焦點機制還沒有特別的清楚，所以不知道如何下手去處理一些不符合預期的現象。其實這些現象如果跟著源碼去看的話，會發現它的實現都是有一定道理的。
- 客觀因素是某些的UI交互比較復雜，Andorid原生的焦點機制只是采用了比較折中的處理方案。沒有什么語言是完美的，也沒有什么框架是完美的，能滿足我們需求才是最好的。所以我認為焦點問題的處理應該建立在我們有一套統一的UI交互的基礎上，然后我們在去基于Android原生焦點機制做一些定制化的操作，具體如何定制化，基本上問題都可以在文中提到的幾個回調接口中去處理。
