我实现了一个具有回收器视图的折叠工具栏布局,如附带的示例代码所示.我的问题是,当我把这个列表向下排列时,它不会一直到顶端.
会发生什么,滚动停止在AppBarLayout应该结束的地方.
我想要的效果是将列表向下移动,列表将一路向上,并显示/展开AppBarLayout
我的minSdk是14.任何帮助或建议是非常感谢.
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.AppBarLayout>
<android.support.design.widget.CollapsingToolbarLayout
app:layout_scrollFlags="scroll|exitUntilCollapsed">
<LinearLayout
app:layout_collapseMode="parallax">
//some elements
</LinearLayout>
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<android.support.v7.widget.RecyclerView
app:layout_behavior="@string/appbar_scrolling_view_behavior"/> //value android.support.design.widget.AppBarLayout$ScrollingViewBehavior
<android.support.v7.widget.Toolbar
app:popupTheme="@style/AppTheme.PopupOverlay"
app:layout_collapseMode="parallax" />
解决方法
您可以使用
setExpanded()方法完全展开或折叠App Bar.一个实现可能会覆盖您的Activity类中的dispatchTouchEvent(),并根据是否在中间点折叠来自动折叠/展开您的App Bar：
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_UP) {
float per = Math.abs(mAppBarLayout.getY()) / mAppBarLayout.getTotalScrollRange();
boolean setExpanded = (per <= 0.5F);
mAppBarLayout.setExpanded(setExpanded,true);
}
return super.dispatchTouchEvent(event);
}
关于自动滚动到最后的位置,我在GitHub上放了一些代码,显示如何programmatically smooth scroll to a specific location可能有帮助.调用滚动到list.size() – 1在一个逃跑的例子可以复制的行为.这部分代码的方式是从StylingAndroid和Novoda博客改编：
public class RecyclerLayoutManager extends LinearLayoutManager {
private AppBarManager mAppBarManager;
private int visibleHeightForRecyclerView;
public RecyclerLayoutManager(Context context) {
super(context);
}
@Override
public void smoothScrollToPosition(RecyclerView recyclerView,RecyclerView.State state,int position) {
View firstVisibleChild = recyclerView.getChildAt(0);
final int childHeight = firstVisibleChild.getHeight();
int distanceInPixels = ((findFirstVisibleItemPosition() - position) * childHeight);
if (distanceInPixels == 0) {
distanceInPixels = (int) Math.abs(firstVisibleChild.getY());
}
//Called Once
if (visibleHeightForRecyclerView == 0) {
visibleHeightForRecyclerView = mAppBarManager.getVisibleHeightForRecyclerViewInPx();
}
//Subtract one as adapter position 0 based
final int visibleChildCount = visibleHeightForRecyclerView/childHeight - 1;
if (position <= visibleChildCount) {
//Scroll to the very top and expand the app bar
position = 0;
mAppBarManager.expandAppBar();
} else {
mAppBarManager.collapseAppBar();
}
SmoothScroller smoothScroller = new SmoothScroller(recyclerView.getContext(),Math.abs(distanceInPixels),1000);
smoothScroller.setTargetPosition(position);
startSmoothScroll(smoothScroller);
}
public void setAppBarManager(AppBarManager appBarManager) {
mAppBarManager = appBarManager;
}
private class SmoothScroller extends LinearSmoothScroller {
private static final int TARGET_SEEK_SCROLL_DISTANCE_PX = 10000;
private final float distanceInPixels;
private final float duration;
public SmoothScroller(Context context,int distanceInPixels,int duration) {
super(context);
this.distanceInPixels = distanceInPixels;
float millisecondsPerPx = calculateSpeedPerPixel(context.getResources().getDisplayMetrics());
this.duration = distanceInPixels < TARGET_SEEK_SCROLL_DISTANCE_PX ?
(int) (Math.abs(distanceInPixels) * millisecondsPerPx) : duration;
}
@Override
public PointF computeScrollVectorForPosition(int targetPosition) {
return RecyclerLayoutManager.this
.computeScrollVectorForPosition(targetPosition);
}
@Override
protected int calculateTimeForScrolling(int dx) {
float proportion = (float) dx / distanceInPixels;
return (int) (duration * proportion);
}
}
}
编辑：
以上代码片段中的AppBarManager是指用于与活动中的AppBarLayout通信的界面.使用动画来折叠/展开应用程序栏方法.最终的方法用于计算屏幕上可见的RecyclerView行数：
public interface AppBarManager {
void collapseAppBar();
void expandAppBar();
int getVisibleHeightForRecyclerViewInPx();
}
public class MainActivity extends AppCompatActivity implements AppBarManager{
@Override
public void collapseAppBar() {
mAppBarLayout.setExpanded(false,true);
}
@Override
public void expandAppBar() {
mAppBarLayout.setExpanded(true,true);
}
@Override
public int getVisibleHeightForRecyclerViewInPx() {
if (mRecyclerFragment == null) mRecyclerFragment =
(RecyclerFragment) getSupportFragmentManager().findFragmentByTag(RecyclerFragment.TAG);
int windowHeight,appBarHeight,headerViewHeight;
windowHeight = getWindow().getDecorView().getHeight();
appBarHeight = mAppBarLayout.getHeight();
headerViewHeight = mRecyclerFragment.getHeaderView().getHeight();
return windowHeight - (appBarHeight + headerViewHeight);
}
